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Compass and Altimeter


Artifact

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I'm trying to decide between the 76CSx or just the 76Cx, and it seems the only difference whatsoever is the compass and altimeter. For those of you that have the 76CSx (or the 60CSx), do you find yourself using the compass and/or altimeter a lot? Does it ever really come in handy or is it more a novelty feature? And is the altimeter any more accurate then getting the elevation from GPS?

 

The price difference between the CSx and the Cx isn't massive (about $60-70 CDN) but I'd still like to put that money towards maps instead if it's a feature I'll never use anyways.

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I'm trying to decide between the 76CSx or just the 76Cx, and it seems the only difference whatsoever is the compass and altimeter. For those of you that have the 76CSx (or the 60CSx), do you find yourself using the compass and/or altimeter a lot? Does it ever really come in handy or is it more a novelty feature? And is the altimeter any more accurate then getting the elevation from GPS?

 

The price difference between the CSx and the Cx isn't massive (about $60-70 CDN) but I'd still like to put that money towards maps instead if it's a feature I'll never use anyways.

 

It seems to be a rather passionate choice by both parties (those that like it and those that don't want it) where both feel strongly in their decision. Personally I fall into the category liking the compass very much (60CSx). Here's why, I use mine for hunting and when ever you stop to look around and listen and then want to start walking again toward your intended destination without the compass you could easiy have no idea or general direction in which to start walking until you have walked several yards (could be 180 degrees in the wrong direction), which usually has to be at a rate above 2 mph. before the satellites will show you your direction of travel. The same situation could occur intransit to a cache.

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That's true, and I haven't done any geocaching yet (like I said I'm planning to start this spring) but I would imagine that would happen quite a bit while looking for a cache. On the other hand, I've never really had trouble remembering which general direction I was heading in even if the area is unfamiliar.

 

I guess the purpose of a compass is pretty obvious and it would also be very easy to bring a physical compass along as well (probably a good idea for emergencies anyways) so what I'm really not sure about is the altimeter. Are there any situations where the altimeter would help you or provide any real use besides letting you log how high you've climbed for your own records?

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Artifact,

 

I don't have the 76CSx or the 76Cx but I do have a Vista HCx and the Compass and Altimeter functions the same. Justly like eaparks staid I use mine for hunting and caching and I like the compass. With that said there are few things you do have to be aware of: the compass needs to be calibrated regularly, which for me is every time I use it because I always start out with fresh batteries. The other thing I found that prevented sluggishness was to change the threshold for when the compass is active from 2 miles an hour to 10 miles and hour so basically it always enabled when I am walking. Changing the threshold also seemed to tighten up my tracking so my error was no more then 30 ft on track backs. Regardless of the brand or model I would recommend the compass if it is available and you can afford it.

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Are there any situations where the altimeter would help you or provide any real use besides letting you log how high you've climbed for your own records?

It depends - do you need / want to know your elevation reasonably accurately and reliably or not? In general, you probably won't need it for geocaching, but if you want accurate elevation profiles in your tracklogs for example (especially if you are travelling on rough terrain or heavy tree cover) then an auto-calibrating barometric altimeter is highly recommended.

 

A properly used auto-calibrated Garmin barometric altimeter will maintain elevation accuracy of around +/- 5 metres all day, even when reception conditions are variable or poor. In good reception conditions, your GPS elevation will USUALLY be good to within about 10 metres, but it can go WAAAY outside this range from time to time (50 metres error or more is not out of the question), especially when reception conditions are sub-optimal (e.g under heavy tree cover, in deep canyons and gullies, or in high-rise urban areas).

 

Hope this helps!

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It really comes down to what you want out of your GPS. A barometric altimeter is really only good for a day or so (longer if the weather is stable) before pressure changes will throw you off. I've gone to sleep only to wake up with my altimeter putting me 100 meters lower then I was when I closed my eyes. Even with auto calibration you can have HUGE inaccuracies over the period of a days. Oc course, if you are on a multiday caching trip, you can look for some BM's and correct and weather related inaccuracy.

 

Outside of geocaching I navigate exclusively with map and compass. No batteries to die, no sats to lose in deep cover, UTM's give me accurate (+/- 10m) location (including altitude), and I get a much better view of the world around me (14.5km N/S and 10.5 km E/W) then a tiny GPS screen.

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A barometric altimeter is really only good for a day or so (longer if the weather is stable) before pressure changes will throw you off. I've gone to sleep only to wake up with my altimeter putting me 100 meters lower then I was when I closed my eyes. Even with auto calibration you can have HUGE inaccuracies over the period of a days.
When you talk about going to sleep and waking up with the altimeter showing an elevation different by 100 meters from the previous day, presumably you turned the GPS off when you went to sleep. In that case, what you describe is not surprising: auto calibration works only when the GPS has a satellite fix. It can’t work when the GPS is off.

 

The solution is to note the elevation shown on the barometric altimeter before you turn it off at the end of the day. Then the next morning, after achieving a good satellite fix, manually calibrate the altimeter to the reading you had at the end of the previous day. By following this procedure, you will not only eliminate huge inaccuracies, but in fact achieve very good accuracy, regardless of changes in weather. This has been documented previously by julianh, in one of his many excellent posts on this topic:

In my travels, I generally have SOME points of known elevation - sometimes, several such points each day; sometimes not at all for several days.

 

For example. whenever my travels take me to the coast, I can walk down to the water's edge, and be pretty sure I am at sea level (plus or minus a metre or two, allowing for tides, etc). For my remote site investigations, the project "base camp" may have been surveyed, so I will know the elevation of the camp office or similar. I sometimes have access to limited topo maps, which might pick up the tops of major hills or similar, but might be very light on for contours generally in the main areas of interest (or may even be non-existent).

 

That is, I often have no credible topo data for most of the areas I am inspecting. One of my tasks is often to do some preliminary terrain reconnaissance before we send in the surveyors and / or order aerial photography / LIDAR / etc to get quality topo data for the area in question. What I will typically do each day is as follows:

 

1) At the start of the day, turn on the GPS at a location with good sky visibility, let it "soak" for 15 minutes or so, and calibrate the altimeter. (Generally, I know the elevation of my start point, because it is where I finished up the previous day.)

 

2) A I travel through the day, I will frequently make a note of my auto-calibrated barometric elevation, and my GPS elevation. When I have good sky visibility, the two elevations will generally match pretty well (to about 3 to 5 metres typically). However, when my sky visibility is poor (under heavy rain-forest, in deep ravines, half the sky blocked because I am at the base of a big escarpment, etc), the two elevation readings can vary by significantly bigger margins - 10 to 20 metre difference is not unusual under poor sky visibility, 50 metres is not unknown. As explained previously, the GPS elevation can be expected to be in error whenever you don't have a good sky view, but the auto-calibrated barometric elevation will retain good accuracy through such circumstances.

 

3) Whenever I get to any location with reliable elevation data, I will ALWAYS make a note of the two elevation figures, to make sure that my current elevation reading is still well calibrated.

 

4) At the end of the day's travels, I will ALWAYS make a note of my reported auto-calibrated barometric elevation, even if I have no reliable figure for the "official" elevation of my location, as this will be the starting elevation I will use the next day.

 

On the basis of these practices, I am confident that my GPSr maintains auto-calibrated barometric elevation accuracy of about 5 metres or better almost all of the time, but may occasionally drift out to about 10 metres worst case, but the auto-calibration routine will self-correct such errors, so it will draft back into plus or minus 5 metre accuracy (approximately) pretty quickly. My GPS elevation is good to about 5 to 10 metres MOST of the time, but can easily drift out to 20 metre error (or worse) from time to time, especially in locations with a poor sky view.

In this post from the same thread, he discussed the environments in which he has used his unit and made his observations:

In the last 6 months, I have used my GPSr in the high Andes (> 3,500 m elevation to sea level in a single day), Indonesia (sea level to 500 metres elevation in a day), New Caledonia (sea level to 250 metres several times each day), and numerous trips around Australia (sea level to around 1,000 to 1,500 metres on a typical trip).

 

The nature of my work is that it is simply not possible for me to get quality topo mapping for the remote areas I go to on short notice, so I really rely on my GPSr to track my elevation. Because of the lack of topo mapping, I can't verify my elevation accuracy every step of the way, but I do get the opportunity to check my elevation from time to time - e.g. each time I return to "base camp", or whatever.

 

My experience is that my Summit HC almost always reports elevation to about 5 metre accuracy, regardless of weather conditions - and believe me, the weather can change extremely rapidly in the high Andes, or in the Indonesian jungle in the wet season! Occasonally, my elevation accuracy may drop to about 10 metres (especially if I have been travelling in a car or speed boat, or in extremely windy conditions), but once I get back on foot, and give the unit half an hour or so to settle down, my elevation accuracy will generally be back to about 5 metres accuracy - without any manual intervention or recalibration.

Edited by roybassist
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Just my 2 cents worth here but I find the electronic compasses on GPS units to be nearly worthless. They update slowly, act erratically, require frequent calibration, only work when holding the unit level (Garmin) and are holding still. I have little use form them after trying it out on 4 different units and owning 1 with the feature.

 

Still - I must admit that many cachers will tell you it is invaluabloe and the only way to cache. Not me.

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Not that I have used one with or without the compass yet but I think I would feel the same way about the electronic compass. And I would always carry a physical compass with me anyways. And I read in some review somewhere that the compass feature drains the batteries faster? Not sure how true that is.

 

Basically it comes down to $60 for the altimeter. Some great tips to get the most of the altimeter have been posted but one thing I don't really know is when the altimeter would come in handy during practical use.

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If you are in a dense forest with a handheld GPS without a compas, you are more or less lost! Using the satelites for finding north requires you are MOVING if you want an accurate reading. I don't recall how many times I have been jumping up-and downhill for finding North, before I bought my GPS with compass! Love my 76CSx

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IMHO I like the compass and alt. Better to have them and not use them than not have them at all IMHO. The compass works great when you are hunting and in places where movement is so slow that the gps really can't tell what direction you are heading. It is like buying a car with air conditioning here in Montana where you don't use it much but it is nice to have at times. You can't go wrong with Garmin either.

Edited by Team Sidewinder
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@ bcooper14: Iwas actually very interested in the PN-40, it looks like a great unit but I'ma bit worried about buying one because it doesn't seem to be compatible with Mac computers, and I would needa GPS that I can easily get topo maps of Canada for. Or is the Delorme base map detailed enough for geocaching?

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They do seem to have good customer service. But there is one thing I am concerned about. I have also asked about the PN-40 on the Delorme forums users there do the same thing when I ask if the product is Mac compatible, they link me to those poll threads, which have a lot of info but basically what I am getting from them is that there is no Mac compatibility as of now and it may or may not be happening.

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Hi Artifact,

 

I went through this same exercise when trying to decide between the eTrex Legend HCx and Vista HCx. Same issue: only difference is the electronic compass and barometer. I bought the Legend (without them) because:

 

- It's cheap to get a decent compass, which doesn't have all the well-documented hassles of the built-in electronic one. It was even easier for me because I already own a moderately decent one (that I almost never use).

 

- I could care less what my elevation is to any degree of accuracy greater than a few hundred meters. Most times I don't care at all and, rarely, I'm simply curious, say, if I'm breathing a little harder as I walk. I simply don't do anything, even when I'm tramping or riding my mountain bike around the Rocky Mountains, that requires me to know what altitude I'm at. And If I want to know with reasonable accuracy I just look at the nearest contour on my topo map, which I always have loaded when I'm in the mountains. Out here on the Canadian Prairies, where I spend most of my time, altitude is not an issue at all. We don't have any to speak of. :laughing:

 

Oh yeah, if I want to know what the weather might be, I check the Weather Network or Weather Canada's website for the general trend before I head off into the uncharted wilderness. I figure if they can't get it right more than the next few hours, with all their trained experts and computer systems, how am I going to do any better with my ignorance and a barometer? :laughing:

 

For those who find these extras useful, I'm not trying to make an argument. I just want to let Artifact know that some of us don't. Not because they might not have any inherent Goodness, but just because we have no personal use for the information. What we do doesn't require it, and we, otherwise, have no, or miminal, interest in the information for its own sake. That it's okay to admit that he won't care at all about what they can tell him, if that's where he finds himself at the end of this discussion.

 

As he mentioned in his first post, the money might well be better spent on some good maps ... including some topos if he might have an interest in his elevation from time to time ... and a cheap compass if he might occasionally get into a situation where one would be useful.

 

...ken...

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Ken in Regina you basically summed up what I was thinking before I started this thead. I just didn't want to be the one wierdo out there who didn't care what altitude he was at :laughing:

I have a pretty good physical compass already so I'm not too worried about the built in compass and like you said, and maybe I should just take the extra money that the CSx would cost and put it towards a really good topo map with fairly accurate contour lines to begin with. I'll probably have the compass and altimeter turned off most of the time anyways because I'm always paranoid about battery drainage. Who knows, by the time I place the order for the unit I may just not care anymore and spend the extra $60 on the CSx, but to be honest I don't think I'll ever need them.

 

By the way, does anyone know if Garmin plans to release a new line of handheld GPS units that will be replaced the 60 and 76 series any time soon? Or is Garmin just focusing on the Oregon and Colorado series now?

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