GPS Units

March 23, 2008

Hello, I am new to forums and have discovered that there are some hot topics around here LOL. Well, anyway on to my question...

I am looking into getting a new handheld GPS unit for our family. However, I have looked until my eyes were cross-eyed! There are about a million different choices and their all the best. I was wondering if you seasoned cachers could do a little product review for me so I can get an idea what to upgrade too.

THANKS :laughing:

March 23, 2008

Garmin appears to be the unit of choice due to their excellent support. (mac users are probably rolling around laughing hysterically and choking on bits of their own vomit)

It has to be a model with and H (high sensitivity, different chip but same performance as the 60CSx) An x in the name is also good, means unlimited data storage with removable micro sd cards, this is a very good thing.

The difference in price between the crippled models and the top of the range etrex, the VistaHCx is so small that you need not bother with the others unless you are really super strapped for cache (cash). The VistaHCx will set you back about $220 and it does everything, in a solid compact package.

HCx, nice ergonomics, not any larger than it needs to be. Great battery life, bright screen, takes auto routing maps. Plenty of geocaching tools. Believe me you can do all the research again but we've already done it for you, which is why you are asking I suppose.

Performance is the same as the long in the tooth formerly top dog 60CSx which appears laughably oversized by comparison.

Edited March 23, 2008 by gallet

2.5k · March 23, 2008

Before we go suggesting units randomly, how about you tell us a little about what you need.

What Price range would you be willing to pay?

Will you want Mapping, either Roads and/ or Topo data?

Is it important that it guide you with auto routing to your destination?

How technical are you, will you want one with lots of bells and whistles, or a basic easy to run unit?

What are you going to use it for? (Geocaching, hiking, driving, boating, etc....)

2.3k · March 23, 2008

Hi All

I have been reading the Forum and now I'm completely confused!! :anibad: :blink: :unsure:

I want to upgrade my Legend and have narrowed the field down to the Vista HCx and the 60CSx. I would be keen to hear suggestions / recommendations and especially Airmapper's response. :huh:

Happy caching

cincol

11.3k · March 23, 2008

Because I have the Vista HCx, I would recommend that GPS unit. :anibad:

I have both City Navigator and Topo maps on my HCx. Although it can be used for Geocaching without maps, having at least the Topo maps helps a lot. Depending on where you drive, the auto-routing City Navigator maps could be unnecessary . . . or very necessary. :unsure:

March 23, 2008

Before we go suggesting units randomly, how about you tell us a little about what you need.

What Price range would you be willing to pay?

Will you want Mapping, either Roads and/ or Topo data?

Is it important that it guide you with auto routing to your destination?

How technical are you, will you want one with lots of bells and whistles, or a basic easy to run unit?

What are you going to use it for? (Geocaching, hiking, driving, boating, etc....)

You have illustrated my point. Unless one is desperately short of $70 which is basically the difference between an OK to use crippled model and the so called 'bells and whistles' model, there's no reason to not get the best.

The ability to add auto routing maps at a later stage does not add any weight or size or complication to the unit. Easy to use? they are all as easy to use as each other. Too complicated to work out the barometric altimeter? Don't worry it's not compulsory to use and it will prove to be amusing one day. Having a proximity alarm does not make it more difficult to mark a waypoint. etc.

regarding the 60CSx vs VistaHCx, do a forum search, it's been done to death.

2.1k · March 23, 2008

Unless one is desperately short of $70 which .........there's no reason to not get the best.

That's right - get the best. There are only two classes of things to buy in this life: necessities and luxuries.

Now, true necessities are just that and one can not do with out them by definition. For true necessities, one must have the best. How can one compromise on such if it is a true necessity. Therefore, one just has to spend on whatever it takes to aquire whatever is the best.

Fortunately, it's different for luxuries. Here, one has to spend whatever it takes to aquire the best. What kind of luxury would it be if it were just a crummy stand-in for the best? A cheap, feature deficient item and luxury are a contradiction in terms. Therefore, one just has to spend on whatever it takes to aquire whatever is the best.

2.1k · March 23, 2008

Too complicated to work out the barometric altimeter? Don't worry it's ........

basically useless. I have one and do leave home without it all the time.

March 23, 2008

For true necessities, one must have the best...Therefore, one just has to spend on whatever it takes to aquire whatever is the best.

Fortunately, it's different for luxuries. Here, one has to spend whatever it takes to aquire the best.

You don't appear to have thought this one through very well.

March 24, 2008

Garmin eTrex H works for me :unsure:

At the cheap end of the scale, no maps etc etc.....

You can pay more if you want more but if you just want a unit that keeps its lock on satalites under dense tree cover, then you can't go wrong with the eTrex, but make sure it's the 'H' model.

Another nice feature is the easy grip one handed use of the Garmin units. I like that I have to press hard on the buttons, it's saves me from makeing unwanted selections.

It's also bright yellow and easy to see when you put it down on the forest floor. it's waterproof and runs for 17 hours on 2xAA batteries. The screen is easy to see in bright sunlight and nice and easy on the eyes in the evening with the backlight turned on.

When my eTrex H arrived it had the WAAS turned off, which I found strange as this is an enhancement to the accuracy of the unit. So make sure that you go into the settings and turn on WAAS.

And don't splash out on the PC link cable, it's dog easy to make your own from and old serial lead, a glue gun and a thin piece of plastic :anibad:

2.1k · March 24, 2008

For true necessities, one must have the best...Therefore, one just has to spend on whatever it takes to aquire whatever is the best.

Fortunately, it's different for luxuries. Here, one has to spend whatever it takes to aquire the best.

You don't appear to have thought this one through very well.

Actually, it's exquisitley well thought out. However, it's a very well understated thought reversal expressed in a tongue in cheek fashion.

Mull it over for a bit, a week will do. And if it doesn't come through, post back and I'll offer some examples for purposes of elucidation. :unsure:

March 24, 2008

For true necessities, one must have the best...Therefore, one just has to spend on whatever it takes to aquire whatever is the best.

Fortunately, it's different for luxuries. Here, one has to spend whatever it takes to aquire the best.

You don't appear to have thought this one through very well.

Actually, it's exquisitley well thought out. However, it's a very well understated thought reversal expressed in a tongue in cheek fashion.

Mull it over for a bit, a week will do. And if it doesn't come through, post back and I'll offer some examples for purposes of elucidation.

Team Cowboy Papa : I get your point, and saw your humor, but a weeks wait? Come on, roll out the

examples, the popcorns almost ready! ;^)

Norm

March 24, 2008

For true necessities, one must have the best...Therefore, one just has to spend on whatever it takes to aquire whatever is the best.

Fortunately, it's different for luxuries. Here, one has to spend whatever it takes to aquire the best.

You don't appear to have thought this one through very well.

Actually, it's exquisitley well thought out. However, it's a very well understated thought reversal expressed in a tongue in cheek fashion.

Mull it over for a bit, a week will do. And if it doesn't come through, post back and I'll offer some examples for purposes of elucidation.

Very generous of you to offer to explain it to me, I'll take you up on that.

OK, so with luxuries one needs to spend whatever it takes, but on necessities one needs to spend whatever it takes.

Looking forward to the explanation.

2.1k · March 24, 2008

For true necessities, one must have the best...Therefore, one just has to spend on whatever it takes to aquire whatever is the best.

Fortunately, it's different for luxuries. Here, one has to spend whatever it takes to aquire the best.

OK, due to popular demand........

Well, this it's different for luxuries this was the twist. One would be expecting me to say that they are opposites and therefore different, so I introduced it as different, but then went on as if they were the same.

Which to me they are, and the examples:

Necessity:

1. An immediate family member of 50 years of age,or less, has been diagnosed with cancer.

2. Prognosis is 30% chance of recovery and survival with surgery, 60% with radiation therapy and 90% with chemotherapy.

3. I consider any of these treatments to be a necessity of life, particularly the chemotherapy.

4. I would spend every last cent to provide that treatment.

Luxury:

1. I have no penchant for jewelry, bling or baubles, but in the spirit of the example: If I need a wristwatch to show nothing more that simple time and perhaps and alarm function, then a $20 to $40 Casio will do me just fine, would it not?

2. However, I'm into luxuries and need to show them off to soothe and quell my identity crisis so I'm looking at a Rolex, a La Tourneau, and a Giuseppe Versache Linguini at $4,000, $5,000 and $6,000, respectively.

3. Well, I'll buy the most expensive that my assets will allow, would I not. I mean if with the Rolex I'm spending $3,960 above and beyond basic functionality for purposes of vanity, why not $4,960 or $6,960, if possible?

So those are my conclusions. If it is truly a necessity, one must spend what it takes. For a luxury, why stop at minimal frivolities?

Edited March 24, 2008 by Team CowboyPapa

March 25, 2008

For true necessities, one must have the best...Therefore, one just has to spend on whatever it takes to aquire whatever is the best.

Fortunately, it's different for luxuries. Here, one has to spend whatever it takes to aquire the best.

OK, due to popular demand........

Well, this it's different for luxuries this was the twist. One would be expecting me to say that they are opposites and therefore different, so I introduced it as different, but then went on as if they were the same.

Which to me they are, and the examples:

Necessity:

1. An immediate family member of 50 years of age,or less, has been diagnosed with cancer.

2. Prognosis is 30% chance of recovery and survival with surgery, 60% with radiation therapy and 90% with chemotherapy.

3. I consider any of these treatments to be a necessity of life, particularly the chemotherapy.

4. I would spend every last cent to provide that treatment.

Luxury:

1. I have no penchant for jewelry, bling or baubles, but in the spirit of the example: If I need a wristwatch to show nothing more that simple time and perhaps and alarm function, then a $20 to $40 Casio will do me just fine, would it not?

2. However, I'm into luxuries and need to show them off to soothe and quell my identity crisis so I'm looking at a Rolex, a La Tourneau, and a Giuseppe Versache Linguini at $4,000, $5,000 and $6,000, respectively.

3. Well, I'll buy the most expensive that my assets will allow, would I not. I mean if with the Rolex I'm spending $3,960 above and beyond basic functionality for purposes of vanity, why not $4,960 or $6,960, if possible?

So those are my conclusions. If it is truly a necessity, one must spend what it takes. For a luxury, why stop at minimal frivolities?

Team Cowboy Papa :

My take on your statement was a little different, and a little the same.

What I heard (while reading) was that everyone is different; what their needs (necessities) are, and what

they consider to be luxuries can be very similar or very different. The point of division between these two

categories may be close, or far, comparatively, but will always be different, and one would be prudent to

spend what was necessary to obtain the best item that fit within either of those separate categories,

dependent on one's mindset.

Norm

edit : punctuation

Edited March 25, 2008 by RRLover

March 25, 2008

Team Cowboy Papa :

My take on your statement was a little different, and a little the same.

What I heard (while reading) was that everyone is different; what their needs (necessities) are, and what

they consider to be luxuries can be very similar or very different. The point of division between these two

categories may be close, or far comparatively, but will always be different, and one would be prudent to

spend what was necessary to obtain the best item that fit within either of those separate categories,

dependent on one's mindset.

Norm

My take was that it was illogical nonsense. I also take exception to the paps's post when a quote was taken from my post and was then truncated with his own conclusion added, namely that the barometric altimeter is 'useless'. The way to do this is just to state a contrary opinion not to put words into someone elses mouth.

I do wryly note that TCP also states he has the 'useless' barometric altimeter. Which reminded me of a thread I started about the fluxgate compass. One person came on there to wax about the uselessness of this feature and stated that he tells all his students not to get that feature, he also admitted to having it himself.

If there's one thing that is annoying on forums it's when someone deliberately gives bad advice that one would not follow oneself in order to make a non existent point.

March 25, 2008

Team Cowboy Papa :

My take on your statement was a little different, and a little the same.

What I heard (while reading) was that everyone is different; what their needs (necessities) are, and what

they consider to be luxuries can be very similar or very different. The point of division between these two

categories may be close, or far comparatively, but will always be different, and one would be prudent to

spend what was necessary to obtain the best item that fit within either of those separate categories,

dependent on one's mindset.

Norm

My take was that it was illogical nonsense. I also take exception to the paps's post when a quote was taken from my post and was then truncated with his own conclusion added, namely that the barometric altimeter is 'useless'. The way to do this is just to state a contrary opinion not to put words into someone elses mouth.

I do wryly note that TCP also states he has the 'useless' barometric altimeter. Which reminded me of a thread I started about the fluxgate compass. One person came on there to wax about the uselessness of this feature and stated that he tells all his students not to get that feature, he also admitted to having it himself.

If there's one thing that is annoying on forums it's when someone deliberately gives bad advice that one would not follow oneself in order to make a non existent point.

I'll neither condemn nor defend other's perceptions of transgression-

I can only say that GPSrs have some things in common w/ cable TV and new cars; you can't always pick

exactly which options you want, without getting some you may not need. At least that's going to be the

case until there's an opensource receiver marketed somewhere! Until then one has to settle, and accept:

t'aint nothin' gonna be perfect. Only you can decide what "floats yer boat"!

I'll step back now before the real "sprinkling" starts.

Norm

Edit :

OP : see #3 above

Edited March 25, 2008 by RRLover

March 25, 2008

@'RRLove

I'll neither condemn nor defend other's perceptions of transgression-

A wise position to take.

...without getting some you may not need...

Aye, there's the rub. The difference in price between a top range model car and a bottom range model is a lot, same for cable tv's. But the OP is asking about gpsR's which I suppose is to be expected on a gps forum. Which takes me back to my original point, the difference between a crippled etrex and the top range is really just small change for most people.

Some people suggest that the HCx has so many features that it would just be confusing to the newbie cacher. I find this to be a condescending attitude. The extra functions are in the software which one can use or not, it's not like there are lots of extra buttons or anything.

No one is going to complain after purchase that they wish they didn't get a unit that had auto routing because it's an invisible feature until maps are installed. But plenty of people have bought gps for geocaching with no intention of installing road maps but later regret this and end up upgrading.

So I suggest that one should always seriously consider the small extra cost of an HCx as opposed to say the VentureHC, because that "may" may end up being rather expensive down the track.

Another example, why would anyone want to buy a LegendHCx as opposed to a VistHCx just to save $20? The argument goes something along the lines of "I'd never go bush without a Silva compass, what if my gps croaks" Yes it is most wise to take a back up, but remember that the compass on the gps is also a back up for a manual compass.

No one is ever going to regret spending $20 on the Altimeter and Compass. The Altimeter is for many people useless but fun and it's basically free because the fluxgate compass is worth the $20. So what's wrong with getting a free Altimeter, it doesn't weigh more, you don't have to use it, it costs no battery power.

March 25, 2008

Here's my two cents worth of advice on choosing a GPSr. Go for the most and best you think you'd ever want or need, to do what you want. It is pretty clear reading these forums that there are a number of very fine units to choose from. From my own personal experience I can tell you I have spent a lot of time and energy analyzing everything to death ... knowing the best choices but not doing what I really wanted, primarily because of money. You can get a great GPSr for geocaching for $100, or you can spend $300 for a realy great one. When I first started my search I thought that that $200 difference was a lot. It is ... but it isn't.

In the last months I've spent too many hours thinking about what to do. I actually bought a Magellan Meridial Platinum, Explorist 210, and a Garmin Summit HC. They all find caches, and they are all fun. I just got a Garmin GPSMAP 60CSx that will do everything I want. If I had it to do again I would have gone right to the 60CSx (or other top end unit) and saved the time and money spent on the other 3! Sure, I have an extra (3 actually) gps for the grandchildren, but I could have gotten to this point with less stress and cost. Figure it this way ... spending $300 on something you're going to keep and enjoy for years isn't bad.

The only real advice I'd give is to get a high sensitivity unit so it will work better in more places. When you're in heavy woods and the trees get heavy leaves you'll be glad. I find an electronic compass to be useful but I always have a regular compass in my pocket. I also find it reassuring to have something like a local Topo map installed, because it is nice to know "for sure" where and how close roads and civilization is when you're in the woods and every way you look looks the same. lol

Have fun, lighten up, they all work, even the $50 EBay ones.

March 25, 2008

@whitneymvp

Yes, you found out the hard (and expensive way) what I'm trying to explain. The only correction I'd make to your post is that the real world difference between the bottom range Yellow etrex (the only model left that doesn't have the pick stick) and the absolute top range HCx is $100

March 25, 2008

2.1k · March 25, 2008

Ok, here is why I say that the barometric altimeter is useless. I have one and don't use it because it is just that.

So I got out my Casio watch with barometric altimeter and put it on about 10 hours ago.

At that time is was basically correct, displayed 20 feet (it displays in 20 foot increments) based on current ambient pressure. The altitude reading rose steadily during the day, as the high pressure system that we have been under is moving on, to reading 200 feet at this time. For that as a typical example, I find it very unreliable and never use it as a fact.

It is much better to look at the topo on my PN-20 and with its current indicated postion, interpolate between contour lines. Doing so with the contour lines being 20 feet apart, I can estimate my elevation to within 2 or 3 feet.

Geez, how much better do you want it? No way the barometric can come close. I mean, what other issue do you have with it? After all, this isn't rocket science.

Edited March 25, 2008 by Team CowboyPapa

March 25, 2008

@Team CowboyPapa,

Just because you do not know how to use a barometric altimeter does not make it useless.

2.1k · March 25, 2008

@Team CowboyPapa,

Just because you do not know how to use a barometric altimeter does not make it useless.

Please excuse me for wasting your time. It is my complete misunderstanding of the physics of the atmosphere which has led to that result. Unfortunately, such subject matter is beyond my mental capabilities. I should have realized my limitations and ceased pursuing this very intellectually intensive area of knowledge. I guess that it is rocket science after all. :anibad:

March 25, 2008

@'Team CowboyPapa

Please excuse me for wasting your time.

What makes you think you've wasted my time?

It is my complete misunderstanding of the physics of the atmosphere which has led to that result.

It's not a misunderstanding of physics, just a misunderstanding of how to use a barometric altimeter. And there's nothing wrong with that.

Unfortunately, such subject matter is beyond my mental capabilities.

Nah, it's easy to understand that a barometric altimeter is meant to be calibrated regularly, once you realise how it works and is meant to be used.

March 25, 2008

I feel sorry for any Newbie that turns to this thread for some basic help.

If you're new to something you want it explained in some basic detail that's easy to digest, then if you want more info or have more questions like how do I calibrate my altimeter to my map, then someone posts a single easy to understand response.

If I was a Newbie to the world of maps and navigation, I would be lost in this thread.

maybe the thread name needs to be changed to "mine shines brighter than yours and I know more than you about the world the universe, the proper use of big words and the Global Positioning System". That I'm sure would save Newbies from wondering in

Please feel free to pull my post to bits, but don't wait for me to come back with smart answers full of big words.

I feel my job is done here unless someone asks for help :anibad:

March 25, 2008

I feel sorry for any Newbie that turns to this thread for some basic help.

If you're new to something you want it explained in some basic detail that's easy to digest, then if you want more info or have more questions like how do I calibrate my altimeter to my map, then someone posts a single easy to understand response.

If I was a Newbie to the world of maps and navigation, I would be lost in this thread.

maybe the thread name needs to be changed to "mine shines brighter than yours and I know more than you about the world the universe, the proper use of big words and the Global Positioning System". That I'm sure would save Newbies from wondering in

Please feel free to pull my post to bits, but don't wait for me to come back with smart answers full of big words.

I feel my job is done here unless someone asks for help

stuthehiker I am a Newbie here looking for basic help, just as you said above! I was looking for some advice on getting a basic GPS to get me started and you have done exactly that. Thank you! I'm off to get my Garmin eTrex H which I think will be just perfect for a complete novice. (although I found my first cache today sans GPS yippeeee!). Thank you for your easy to understand recommendation.

Sarah

March 25, 2008

stuthehiker I am a Newbie here looking for basic help, just as you said above! I was looking for some advice on getting a basic GPS to get me started and you have done exactly that. Thank you! I'm off to get my Garmin eTrex H which I think will be just perfect for a complete novice. (although I found my first cache today sans GPS yippeeee!). Thank you for your easy to understand recommendation.

Sarah

You're welcome Sarah,

Drop me a message if you get this unit and need any help with it.

Stu,

March 26, 2008

stuthehiker I am a Newbie here looking for basic help, just as you said above! I was looking for some advice on getting a basic GPS to get me started and you have done exactly that. Thank you! I'm off to get my Garmin eTrex H which I think will be just perfect for a complete novice. (although I found my first cache today sans GPS yippeeee!). Thank you for your easy to understand recommendation.

Sarah

You're welcome Sarah,

Drop me a message if you get this unit and need any help with it.

Stu,

Thank you!

March 26, 2008

Ok, here is why I say that the barometric altimeter is useless. I have one and don't use it because it is just that.

So I got out my Casio watch with barometric altimeter and put it on about 10 hours ago.

At that time is was basically correct, displayed 20 feet (it displays in 20 foot increments) based on current ambient pressure. The altitude reading rose steadily during the day, as the high pressure system that we have been under is moving on, to reading 200 feet at this time. For that as a typical example, I find it very unreliable and never use it as a fact.

It is much better to look at the topo on my PN-20 and with its current indicated postion, interpolate between contour lines. Doing so with the contour lines being 20 feet apart, I can estimate my elevation to within 2 or 3 feet.

Geez, how much better do you want it? No way the barometric can come close. I mean, what other issue do you have with it? After all, this isn't rocket science.

Aha! Now it becomes clear!

What TCP REALLY meant to say in his contentious posting was:

"The barometric altimeter in my Casio watch is basically useless, because it does not auto-calibrate."

The barometric altimeters in Garmin GPSrs WITH AUTO-CALIBRATION are a totally different beast however. Sure, the basic pressure sensor is fundamentally the same as in a watch. The big difference is that it is set to auto-calibrate itself using the GPS 3D fix elevation. The really clever thing is that the algorithm in the latest units with latest software updates is apparently "heavily damped" so that it doesn't over-react to the inaccuracy and fluctuations which are inherent in GPS elevation determination, but still corrects for changing air pressure.

All you need to do is set your elevation at the start of the day (by known elevation, topo map, or whatever), and then the unit will auto-calibrate itself for changing air pressure even as your elevation changes, and will therefore provide a much more accurate indication of your elevation all day, under heavy cover, intermittent reception conditions, etc. You will also get updated barometric air-pressure (calibrated to sea level pressure), even as you change elevation all day long. (Oh, and by the way, it reports in 1 metre increments, not 20 foot - 6 metre - increments, because it is actually accurate enough to make it worthwhile reporting at this precision!)

It really does work! I find that I can easily maintain vertical accuracy of 5 metres or better ALL DAY while bush-walking with my Summit HC. That beats any GPS topographic maps that I can get in my area (Australia).

On a recent day-long drive of about 300 km, with 1,000 metre net rise to the lookout at my destination, and 1,000 metre net fall when I returned home again, the altimeter was reading just 4 metres different when I got home, but the air pressure had risen by 11 hPa over the day (which corresponds to about 93 metres apparent drop in elevation on an uncalibrated altimeter!) My elevation at the lookout at the high point of the journey was out by just 3 metres, according to the plaque at the lookout. "Useless"? I think not!

Do you NEED a barometric altimeter? Maybe not.

Do they work? Yes!

Is it "useless"? Only if you currently have no need to know your elevation to better than the precision of the topo maps you have available, and never will need to know. (E.g. what if you ever need to visit a location outside the range of your topo maps? May not be an issue for everyone, but it sure is for me!)

Hope this helps!

2.1k · March 27, 2008

Hope this helps!

Not me, but hopefully those who chose to publicly disagree with me. I said essentially the same thing that you did but maybe you expressed it better.

So, as I said above, take the GPS coordinates as they are shown by the cursor on the screen of one's GPS. Then interpolate between contour lines on the topo map. Therefore, if your position is shown between 7460' and 7500' and you estimate your position to be 1/4 of the distance between those and closer to 7460, then your altitude is close to 7470'.

Consensus has it that the altitude calculated by the GPS is of twice the uncertainty of the determined horizontal postion. Generally, I accept that as true and, if so, makes it much more accurate than my barometric altimeter which shows ±100 feet in variation due to changes is the ambient pressure at the same location. So why would one correct the barometric with the GPS calculated as opposed to using the GPS calculated itself? If your GPS calculated it ±50' and the barometric uncorrected is ±100', the corrected barometric is not going to be less that 50'. As my grandaddy used to say: "You can't make a silk purse out of a sow's ear."

That is just a fact of using the instrumentation at our disposal, nothing more can be done with it. Consequently, in the order of accuracy:

1 Best: Determining altitude from horizontal position on GPSr display as located between contour lines.

2. Good: Using the GPS calculated altitude directly.

3. Last resort: Barometric altimeter (only useless if you have 1 or 2 above).

So that's it folks. I can't say more about it. My last physics lab treatise.

Edited March 27, 2008 by Team CowboyPapa

March 27, 2008

Hope this helps!

Not me, but hopefully those who chose to publicly disagree with me. I said essentially the same thing that you did but maybe you expressed it better.

...

So that's it folks. I can't say more about it. My last physics lab treatise.

Sorry, TPC, but I can't let you have the last word - not when it is still misinformed!

I said essentially the same thing that you did

Errr .. no - you said a barometric altimeter was useless; I contend that when used properly, a GPS auto-calibrated barometric altimeter is far from useless!

So, as I said above, take the GPS coordinates as they are shown by the cursor on the screen of one's GPS. Then interpolate between contour lines on the topo map. Therefore, if your position is shown between 7460' and 7500' and you estimate your position to be 1/4 of the distance between those and closer to 7460, then your altitude is close to 7470'.

No argument from me there - as long as you HAVE an accurate topographic map with closely spaced contours of your current location. (Not always easy to get, for some of the places I go!)

Consensus has it that the altitude calculated by the GPS is of twice the uncertainty of the determined horizontal position.

Again, no argument from me on this one

So why would one correct the barometric with the GPS calculated as opposed to using the GPS calculated itself?

You're not listening to me - for best results, you start with a MANUAL calibration at the start of the day. If you don't know your actual elevation accurately, you can use the GPS elevation as your initial calibration, but this could be out by 20 to 50 metres (or more). Believe it or not, your elevation accuracy under these conditions will actually IMPROVE over the course of the day, as the auto-calibration kicks in! (I know you probably don't believe it, but you need to see it in action to see that it really does work!)

The auto-calibration algorithm in the newest Garmin units is very smart (and a trade secret, so what I am describing is my supposition of how it actually works). As far as I can tell, it is "watching" the trend in GPS altitude versus barometric altitude. It adjusts the barometer calibration to generally follow the trend in GPS altitude, but seems to "damp" the rate of calibration so that the barometer calibration doesn't vary anywhere near as quickly or erratically as the GPS elevation. (I am guessing it does something like limit the assumed maximum rate of change of barometric air pressure to something which is physically feasible.)

Anyway, the point is - IT WORKS! Over the course of a day, your GPS elevation can be expected to oscillate around your true elevation by anything from 20 to 50 metres, say, depending on reception quality etc. Over a reasonably long period, the AVERAGE GPS elevation trend can be used as a very solid basis of calibrating the barometric altimeter, and I think this is what the unit does.

If your GPS calculated it ±50' and the barometric uncorrected is ±100', the corrected barometric is not going to be less that 50'.

Yes, but if you start off with a manual calibration to say 2 to 5 metres accuracy, and have a high-precision ambient air pressure sensor, then the unit can keep 5 metre vertical accuracy ALL DAY - because the barometer is being constantly calibrated for changing air pressure, using the GPS elevation trends as a guide.

As my grandaddy used to say: "You can't make a silk purse out of a sow's ear."

True - but you CAN make an accurate altimeter using a high-precision air pressure sensor, a GPS with a good 3D fix, and a smart auto-calibration algorithm - all of which can be found in the Garmin eTrex HS series!

That is just a fact of using the instrumentation at our disposal, nothing more can be done with it. Consequently, in the order of accuracy:

1 Best: Determining altitude from horizontal position on GPSr display as located between contour lines.

What if the best maps available to you have 50 metre contour interval? Or you can't get reliable topo maps at all? (Anyone got a good topo map for West Kalimantan, Indonesia - my last port of call? )

2. Good: Using the GPS calculated altitude directly.

Not as good as using a properly set-up, auto-calibrated barometric altimeter, I'm afraid!

3. Last resort: Barometric altimeter (only useless if you have 1 or 2 above).

No - a properly set-up, auto-calibrated barometric altimeter on a Garmin HS series will beat the GPS altitude hands-down, and will also be better than a lot of topo maps that I have seen. (Can't comment on the maps built into the DeLorme units, because I haven't used one.)

Seriously - before making any further negative comments on the accuracy of auto-calibrated barometric altimeters, without having actually owned and used one - see if you can find a friend with a Garmin HS / HCx or similar, set it up properly, and see how it works. (Prepare to be surprised!)

I really do hope that this helps!

Edited March 27, 2008 by julianh

March 27, 2008

Too complicated to work out the barometric altimeter? Don't worry it's ........

basically useless. I have one and do leave home without it all the time.

Slightly off topic, I know, but ... a variation on the old classic "Physics 101" exam question:

Q: You need to determine the height of a high-rise building, using the navigational aids available to you. How do you go about this to achieve the best accuracy?

A1: Just read off the contours on a topo map and .... Oh, wait a minute, that won't work!

A2: If you have an uncalibrated Casio watch with a barometric altimeter, you can take a height reading at ground level and another at roof top level. Readings are in 20 foot increments, so your estimate will be good to about 40 feet accuracy (12 metres say), 20 feet (6 metres) at best.

A3: If you have a GPSr without a barometric altimeter, take GPS elevation readings at ground and roof level. Rooftop reading accuracy will probably be "pretty good" (by GPS standards), due to good sky visibility, but ground level accuracy may be poor, due to shielding and multi-path errors. Height accuracy probably no better than 30 to 50 metres say.

A4: If you have a modern GPSr with a properly set-up auto-calibrated barometric altimeter, take elevation readings at ground and roof. Height accuracy will be good to about 2 to 3 metres. (Yes, it will continue to give good height accuracy as you go up in the lift, even though you will lose the GPS signals.)

A5: Another method which will work with any kind of sensor - get a long piece of weightless string, tie the watch / GPSr to the end, and swing it as a long pendulum from the roof of the building to ground level, and measure the period. Weigh the watch /GPSr. Basic mechanics will yield the length of the pendulum, and hence the height of the building.

A6: Take your watch / GPSr to the roof of the building, and drop it off. Time the fall to ground, and calculate the height of the building (taking into account gravitational acceleration and air resistance, etc.) (Note: Single use only - make sure you set your stopwatch accurately at the start and finish of the drop!)

A7: For really accurate height calculations with ANY type of measuring instrument - find the building owner. Offer to give him your watch / GPSr if he will show you the building plans, so you can read off the exact height of the roof.

Sorry, I couldn't resist!

Edited March 27, 2008 by julianh

March 27, 2008

@julianh

Amusing and accurate.

They say that misunderstanding something is worse than not understanding because, if one does not understand at least one can make an effort to learn. But if one *thinks* one understands then one will blithely go around disseminating misinformation.

Interesting to know about the improved algorithms because I have been noticing that my HCx baro altimeter is even more accurate these days. I haven't calibrated it for a long time yet every morning it is reading within 2 metres of my correct altitude, that's before it gets a gps fix.

March 27, 2008

A6: Take your watch / GPSr to the roof of the building, and drop it off. Time the fall to ground, and calculate the height of the building (taking into account gravitational acceleration and air resistance, etc.) (Note: Single use only - make sure you set your stopwatch accurately at the start and finish of the drop!)

It would have to be the GPS that gets dropped due the watch having the stopwatch on it

btw, Great post, my science master would have loved you

March 27, 2008

Hello, I am new to forums and have discovered that there are some hot topics around here LOL. Well, anyway on to my question...

I am looking into getting a new handheld GPS unit for our family. However, I have looked until my eyes were cross-eyed! There are about a million different choices and their all the best. I was wondering if you seasoned cachers could do a little product review for me so I can get an idea what to upgrade too.

THANKS

Etrex H is a good start and gets you into uncomplicated caching; even if you upgrade at a later date

the Etrex then becomes a good starter for the younger members of the family when/if they decide to go it alone

March 27, 2008

I am also a newbie and would value any advice about which GPS to buy. I want mine for hiking and geocaching and have narrowed down the choice between Garmin sTrex Vista Hcx and Garmin Colorado 300.

Anybody have experience of either unit please?

Thanks for any advice.

2.1k · March 28, 2008

The auto-calibration algorithm in the newest Garmin units is very smart (and a trade secret, .........

I know, and so is that vitamin store stuff that will take 50 pounds of in 5 days and if I spill it on my pants all the stains will go away and.........

Unfortunately, there were 536 laws of physics 2 years ago and I don't think that Garmin got a new one last year.

Anyway, the point is - IT WORKS! Over the course of a day, your GPS elevation can be expected to oscillate around your true elevation by anything from 20 to 50 metres, say, depending on reception quality etc. Over a reasonably long period, the AVERAGE GPS elevation trend can be used as a very solid basis of calibrating the barometric altimeter, and I think this is what the unit does.

If your GPS calculated it ±50' and the barometric uncorrected is ±100', the corrected barometric is not going to be less that 50'.

Yes, but if you start off with a manual calibration to say 2 to 5 metres accuracy, and have a high-precision ambient air pressure sensor, then the unit can keep 5 metre vertical accuracy ALL DAY - because the barometer is being constantly calibrated for changing air pressure, using the GPS elevation trends as a guide.

If it did work, why would you bother with the corrected barometric? Just use the GPS elevation trends. There are just certain laws of observational physics, statistics and probability that cannot be violated or invented around. If you want to believe that the earth is flat as you refuse to look far enough to see the curvature, I can't teach you. Again, applying data from a ±50' instrument to a ±100' instrument will not reduce the latter from ±100' to ±50'. So my answer was, and still is, why bother with the supposedly corrected barometric and just use the GPS?

Caution children: Do not try this in court! If the cop writes you up for 75 in a 70mph zone, don't tell the judge that you were only doing 70 by the combination of your conventional speedometer which is being corrected by being wired into your onboard radar gun that you used as a baseball pitching coach and you were in a hurry to get to the vitamin store to get some more magic weight loss pills and...........

Edited March 28, 2008 by Team CowboyPapa

March 28, 2008

Powersfamily, I can only hope you skipped about 90% of this thread... good grief! I've seen some winner hijacks in my time but this one takes the cake.

First, it would be good to know what you are upgrading FROM in order for anyone to give you recommendations on what to upgrade TO.

I have the 60CSx and have the Colorado 400t on order for paperless caching, the 60CSx will either be sold or handed down.

Best of luck to you, not sure what else to say other than it's late and my brain is definitely done for the day after reading this thread.

Edited March 28, 2008 by XopherN71

March 28, 2008

Chill, XopherN71, there's nothing wrong with some robust discussion, we're all grown up people who can decide what to read or not. I for one was grateful for the explanation of the new altimeter algorithms. And I'm certain that there's more interest in this thread than oh say all the 'where's the cheapest place to get an hcx' threads. Plus lets be real, everyone enjoys a good thread argument as long as it doesn't get personal.

March 28, 2008

Anyway... since the topic reads 'What GPS do you recommend' and not 'Advanced algorithm discussions', I'll continue on and disregard your defensive comment.

From what I've read the common choices by brand are the following. Granted this doesn't narrow it down much but it's a fairly complete list, perhaps people can expand on the ones they have used a little further.

Garmin:

http://www.garmin.com

(Good customer service and hardware. Also seems to be the most integrated with the geocaching.com website.)

High Sensitivity and Waterproof

eTrex H

High Sensitivity w/Color Screen, Map Capability and Waterproof

Summit HC

Venture HC

High Sensitivity w/Color screen, Map Capability, Storage Card and Waterproof

Vista HCx

Legend HCx

GPSMAP 60Cx, 60CSx, 76Cx, 76CSx

Paperless Caching, High Sensitivity w/Color screen, Map Capability, Storage Card and Waterproof

Colorado 300, 400t, 400i, 400c

Delorme:

http://www.delorme.com

(Good customer service and undeniably great maps.)

Partial Paperless Caching, High Sensitivity w/Color Screen, Map Capability, Storage Card and Waterproof

Earthmate PN-20

Magellan:

http://www.magellangps.com

(Poor customer service and hit or miss hardware.)

Map Capability and Water Resistant

eXplorist 210

Map Capability, Color Screen, Storage Card and Water Resistant

eXplorist 500, 600, XL

High Sensitivity, Map Capability, Color Screen and Waterproof

Triton 200

High Sensitivity, Map Capability, Color Screen, Storage Card, and Waterproof

Triton 300, 400, 500, 1500

Feel free to correct any errors above, I did the best I could to get a base set of the main differences between the makes and models.

Edited March 28, 2008 by XopherN71

March 28, 2008