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Barometric Altimeter


janandsteve

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Anyone tell me how the Barometric Altimeter works? I have the Garmin 62s, but I'm sure it works similar on Oregons etc. I was wondering physically where the 'pressure' sensor is on my Garmin 62s?

 

I use the elevation plot page to 'monitor' weather. I have ranges of 0.5mb and 45min - that way I can see what the pressure is doing at short time scales therefore can decide if the weather will get worse etc.... The barometer seems to tie in with that of my local weather station on WeatherUnderground, but I was wondering physically where the 'pressure' sensor is on my Garmin 62s? Is it something I can put my hand over and thus get a false reading? I have tried everything and the reading seems pretty constant and as I say does tie in well with the local weather station readinga. The altitude does tie in well with my home location and the actual elevation data on OS maps etc.... it seems pretty accurate, but how does it work? Even indoors there is little difference than outside layed flat on the patio table.....Any info appreciated. Thanks.

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Internally it's simply an electronic barometer. It measures the ambient air pressure. Like most every electronic measuring device, it needs to be calibrated to a known value first (i.e. you tell it "right now the air pressure is 951 mbar" and it remembers that). From the air pressure the altitude can be deducted, but only as long as the weather doesn't change. This is the second calibration involved. Since weather changes frequently, the device can optionally use the altitude calculated from GPS to automatically recalibrate the altimeter, which will keep it accurate to a few meters or so.

 

The Oregons have a small hole in the case (on the back, under the battery cover), I assume that's what allows the barometer to work. The actual sensor would be somewhere inside. Covering it or applying pressure will definitely give you false readings (and some older firmwares actually did that with simple squeezing of the case - newer firmwares "smooth" this out).

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Just remember one thing, the calibrated barometric altimeter may not always jive with your local weather station. Both my 62s units give me different readings (adjusted for a known elevation) that are off by 0.3 and 0.5 inches/hg respectively. As long as I'm never calibrating the sensor by the weather stations reading I should be fine. I can still see what the barometer is doing as the plot is all relative anyway.

 

I have contacted Garmin about this and they said that it's within tolerance for the instrument. I remember the older Magellan Meridians had a setting where you could actually calibrate the sensor and make it read what the local weather station was reporting and then proceed to adjust it for elevation. I wish Garmin had the same option.

 

I digress.

Edited by yogazoo
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I remember the older Magellan Meridians had a setting where you could actually calibrate the sensor and make it read what the local weather station was reporting and then proceed to adjust it for elevation. I wish Garmin had the same option.

 

But they do, don't they? When I go to altimeter calibration, it asks me if I know the correct air pressure, and then I can enter it in mBar. Doesn't that do what you want?

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Thanks to all who replied to my questions; I now have a better understanding.

 

The Garmin 62s has 4 holes in a diamond shape under the battery cover. When I cover these quite hard with my finger, the pressure reading increases by 0.1mb every 7secs or so. I'm just amazed that it is fairly accurate with cover of the battery compartment and my carry sleeve https://buy.garmin.com/shop/shop.do?pID=68890

 

Thanks again.

 

Steve

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I can still see what the barometer is doing as the plot is all relative anyway.

Good point. As it is relative, this means I can still see the trend of increase or decrease in pressure, hence 'predict' what the weather is doing.

 

I remember the older Magellan Meridians had a setting where you could actually calibrate the sensor and make it read what the local weather station was reporting and then proceed to adjust it for elevation. I wish Garmin had the same option.

On the 62s ( and prob the oregons etc ) there is an option to do just that. From the Elevation Plot screen, press Menu, then down to calibreate altimeter, enter, say no to knowing the correct elevation, yes to knowing the correct pressure, and then enter the mb from the local weather station. From the main screen, setup, altimeter and I have the following - auto cal=on, bar mode=fixed elev, press trend=save when pwr on, plot type=baro press. Hope this helps.

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Question for you guys with a oregon 550t. What settings do you prefer with your gps for barometric pressure and elvation? I would like to watch both but, more so barometric pressure.

Thanks, Kevin

 

I have the 62s, but I guess its the same on the Oregons.... I tend to use mine for weather trending, so have the following setup - from the main screen, setup, altimeter and I have the following - auto cal=on, bar mode=fixed elev, press trend=save when pwr on, plot type=baro press. The plot type is baro pressure and I have 2 small datafields at the top - could these be elevation and barometer for what you need? If you want to see the trend data eg elevation over time, you can change plot type and the elevation/time recorded will be displayed on the graph. I dont think there is anyway to display 2 graphs at the same time. I believe with auto cal on, the elevation reading 'auto tunes' to the elevation data from the '4th satellite'.

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I remember the older Magellan Meridians had a setting where you could actually calibrate the sensor and make it read what the local weather station was reporting and then proceed to adjust it for elevation. I wish Garmin had the same option.

 

But they do, don't they? When I go to altimeter calibration, it asks me if I know the correct air pressure, and then I can enter it in mBar. Doesn't that do what you want?

I agree - see my post above - sorry didnt realise you had just answered the question.

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Question for you guys with a oregon 550t. What settings do you prefer with your gps for barometric pressure and elvation? I would like to watch both but, more so barometric pressure.

Thanks, Kevin

 

I have the 62s, but I guess its the same on the Oregons.... I tend to use mine for weather trending, so have the following setup - from the main screen, setup, altimeter and I have the following - auto cal=on, bar mode=fixed elev, press trend=save when pwr on, plot type=baro press. The plot type is baro pressure and I have 2 small datafields at the top - could these be elevation and barometer for what you need? If you want to see the trend data eg elevation over time, you can change plot type and the elevation/time recorded will be displayed on the graph. I dont think there is anyway to display 2 graphs at the same time. I believe with auto cal on, the elevation reading 'auto tunes' to the elevation data from the '4th satellite'.

 

Use PROFILES! Have one profile set up for barometeric pressure and one for elevation. The way I do it is I have a "North Up" profile which I use when I need to look at the map with North Up instead of track up. In that profile I have it set up for barometric pressure and every other profile I set to elevation.

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I can still see what the barometer is doing as the plot is all relative anyway.

Good point. As it is relative, this means I can still see the trend of increase or decrease in pressure, hence 'predict' what the weather is doing.

 

I remember the older Magellan Meridians had a setting where you could actually calibrate the sensor and make it read what the local weather station was reporting and then proceed to adjust it for elevation. I wish Garmin had the same option.

On the 62s ( and prob the oregons etc ) there is an option to do just that. From the Elevation Plot screen, press Menu, then down to calibreate altimeter, enter, say no to knowing the correct elevation, yes to knowing the correct pressure, and then enter the mb from the local weather station. From the main screen, setup, altimeter and I have the following - auto cal=on, bar mode=fixed elev, press trend=save when pwr on, plot type=baro press. Hope this helps.

 

I understand how to adjust the barometer using the local data. That wasn't the "calibration" I was referring to. I apologize for not being clear.

 

What I mean by "Zeroing" out the barometer is this. Currently you can calibrate using known values of either barometric pressure or elevation. If you put in the correct Barometric data the elevation is automatically adjusted, adversly if you input the elevation data you get an adjusted barometeric pressure. What would be ultimately helpful and what the older Meridians used to be able to allow you to do is to zero out the berometer so that you input BOTH the pressure data and elevation data. This effectively zero's out the barometer.

 

Right now, when I leave the 62s on to log barometric data it will, over time, adjust to the correct elevation BUT the baometric pressure is ALWAYS a consitent 0.5 in/hg off of what the local station reading is (meaning that if I calibrate using the correct pressure data I will always get an incorrect elevation) . Retaining the elevation data while at the same time adjusting the barometric reading to match the local station is what I mean when I use the term "zero out" the barometer. Currently the Garmin line of GPS's do not allow you to perform this action. I think it could be easily implemented but, for the same reasons they leave out Temperature from the list of data frames, it would confuse people and make more problems than it solves for most users.

 

I have two 62s models and two Oregon 450's. What I've found is that the barometer sensor calibration (the "zero" state I refer to above) is accurate and matches the local weather station on my 450's but the 62s models are always off by a considerable amount.

 

TEST YOUR Barometer ZERO STATE!:

1)In the Altimeter setup menu - Auto Calibration=ON, Barometer Mode=Variable Elevation, SET UNITS TO "Inches of (hg)"

2)Allow the unit to obtain a decent lock and leave the unit stationary for 2-3 hours.

3)Check the "Barometer" field vs the "Elevation" field. Both can be viewed on the Elevation Plot screen.

4)The elevation should be fairly on the mark. Now check the Barometer data and compae it to your closest weather station.

5)Log the difference between the reading from your unit and the local reading.

6)If desired you can repeat the tests over the course of a few days to average your results.

 

The difference in values between the local reading and the units reading is the amount needed to be adjusted to "zero out" your sensor. This is problematic when the sensor is out of calibration so much that using local barometer data to calibrate the unit will provide you with incorrect elevations up to 150 feet or more. Again, my 450's are dead-on accurate at least within an acceptable margin of error. My 62s's are in need of zeroing. Garmin does not provide the ability so I guess I'll have to live with the results. It would be nice if they had an "Easter Egg" to do this.

 

PS: I understand there will be subtle differences in the pressure recorded at the local station vs my exact location. That said, performing this test over several attemps will smooth out that variance and provide you with the real number your sensor needs to be zeroed out.

Edited by yogazoo
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I can still see what the barometer is doing as the plot is all relative anyway.

Good point. As it is relative, this means I can still see the trend of increase or decrease in pressure, hence 'predict' what the weather is doing.

 

I remember the older Magellan Meridians had a setting where you could actually calibrate the sensor and make it read what the local weather station was reporting and then proceed to adjust it for elevation. I wish Garmin had the same option.

On the 62s ( and prob the oregons etc ) there is an option to do just that. From the Elevation Plot screen, press Menu, then down to calibreate altimeter, enter, say no to knowing the correct elevation, yes to knowing the correct pressure, and then enter the mb from the local weather station. From the main screen, setup, altimeter and I have the following - auto cal=on, bar mode=fixed elev, press trend=save when pwr on, plot type=baro press. Hope this helps.

 

I understand how to adjust the barometer using the local data. That wasn't the "calibration" I was referring to. I apologize for not being clear.

 

What I mean by "Zeroing" out the barometer is this. Currently you can calibrate using known values of either barometric pressure or elevation. If you put in the correct Barometric data the elevation is automatically adjusted, adversly if you input the elevation data you get an adjusted barometeric pressure. What would be ultimately helpful and what the older Meridians used to be able to allow you to do is to zero out the berometer so that you input BOTH the pressure data and elevation data. This effectively zero's out the barometer.

 

Right now, when I leave the 62s on to log barometric data it will, over time, adjust to the correct elevation BUT the baometric pressure is ALWAYS a consitent 0.5 in/hg off of what the local station reading is (meaning that if I calibrate using the correct pressure data I will always get an incorrect elevation) . Retaining the elevation data while at the same time adjusting the barometric reading to match the local station is what I mean when I use the term "zero out" the barometer. Currently the Garmin line of GPS's do not allow you to perform this action. I think it could be easily implemented but, for the same reasons they leave out Temperature from the list of data frames, it would confuse people and make more problems than it solves for most users.

 

I have two 62s models and two Oregon 450's. What I've found is that the barometer sensor calibration (the "zero" state I refer to above) is accurate and matches the local weather station on my 450's but the 62s models are always off by a considerable amount.

 

TEST YOUR Barometer ZERO STATE!:

1)In the Altimeter setup menu - Auto Calibration=ON, Barometer Mode=Variable Elevation, SET UNITS TO "Inches of (hg)"

2)Allow the unit to obtain a decent lock and leave the unit stationary for 2-3 hours.

3)Check the "Barometer" field vs the "Elevation" field. Both can be viewed on the Elevation Plot screen.

4)The elevation should be fairly on the mark. Now check the Barometer data and compae it to your closest weather station.

5)Log the difference between the reading from your unit and the local reading.

6)If desired you can repeat the tests over the course of a few days to average your results.

 

The difference in values between the local reading and the units reading is the amount needed to be adjusted to "zero out" your sensor. This is problematic when the sensor is out of calibration so much that using local barometer data to calibrate the unit will provide you with incorrect elevations up to 150 feet or more. Again, my 450's are dead-on accurate at least within an acceptable margin of error. My 62s's are in need of zeroing. Garmin does not provide the ability so I guess I'll have to live with the results. It would be nice if they had an "Easter Egg" to do this.

 

PS: I understand there will be subtle differences in the pressure recorded at the local station vs my exact location. That said, performing this test over several attemps will smooth out that variance and provide you with the real number your sensor needs to be zeroed out.

 

Firstly, appologies for giving you a rather simplistic answer to your original question and for misunderstanding what your original question was refering to. Thank you for giving us the interesting explanation above. I dont have any experience using the Magellan, so cannot comment on what their capabilities were/are, but I understand the points you are making.

 

My 62s is approx 2 or 3 mbar off my local weather station, which is approx 0.5miles from home - I thought that was pretty accurate for this little device? ( unless the local weather station is off too - it is a La Crosse WS2350 connected to weatherunderground ). Current station is: 1007.7mb and the 62s is showing 1010.1mb. I have not referenced it to anything else, so maybe they are both out to a similar degree?

 

With ref to the zeroing out technique you mention above - does the sensor have a linear function characteristic or would the zeroing be different amounts at different 'ends' of the mb scale? Eg zeroing at 1020mb may be +2mb and at eg 995mb it may be -3mb or +5mb or whatever? Does zeroing only work for a linear characteristic? Maybe the Garmins are non linear and thats why they have not incl the zeroing function? I dunno, just something to throw in for discussion.

 

I notice you use Barometer Mode=Variable Elevation. I tend to use this set to fixed elevation as I am more interested in weather trends. Not very often I climb large hills - fairly flat walking and I also use it on the boat - although that is not always that flat!

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My understanding of the two calibration options on Garmins is that calibrating it to your current elevation, tells it that the current ambient pressure that it is reading = the elevation you input and then it uses that to work out future elevations accurately (unless the weather changes (the ambient pressure at a fixed altitude)).

 

To calibrate it to the correct pressure, you enter the current BAROMETRIC pressure for you location AT SEA LEVEL and then it works out the difference between the ambient pressure that it reads at your location and the barometric pressure at sea level to work out your current altitude (as the pressure difference between altitudes is always the same (unless each altitude is experiencing different weather)). I know that it needs you to enter the pressure at sea level for your current location because it asks for the barometric pressure in the manual and not the ambient pressure. The ambient pressure is the actual pressure at your location and the barometric pressure is calculated sea level pressure using ambient pressure and elevation (explained below).

 

Both these methods are designed to compensate for different weather which causes the ambient pressure at a fixed altitude to change. Neither of these methods actually correct the barometer in the GPS if it is reading the ambient pressure incorrectly. I believe this is calibrated at the factory and then not changeable by the user.

 

The GPS works out the barometric pressure by taking the current ambient pressure that it reads, your current altitude according to it (if this is wrong then the barometric pressure will also be wrong) and then adds the known pressure difference between your current altitude and sea level which gives it the current pressure at sea level for you location.

 

The pressure that you will get from your local weather station is also the pressure at sea level which it will work out using the method above using the elevation of the pressure sensor on the weather station.

 

Can someone tell me if this is all right please? Sorry if I haven't explained it very well. :)

 

One other question is whether anyone knows a reason why the auto calibration in my 60csx almost always calibrates it about 20ft lower than my correct elevation? I am using google earth to give the correct elevation for my location and a non Garmin topo map on the GPS. Even when it is on and at the same elevation (although not the same location) for an entire day, it still calibrates too low. For example when I spent a day out in my boat, I calibrated it at my house to the correct elevation, when I arrived at my boat it was reading about 5ft above sea level (approximately correct as it uses chart datum as sea level) and then at the end of the day, it was reading 15ft below sea level and the tide was at about the same level as it had been in the morning. Can anyone explain a reason for this strange behaviour? :huh:

Edited by Mako-Shark
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Can someone tell me if this is all right please? Sorry if I haven't explained it very well. :)

 

One other question is whether anyone knows a reason why the auto calibration in my 60csx almost always calibrates it about 20ft lower than my correct elevation? I am using google earth to give the correct elevation for my location and a non Garmin topo map on the GPS.

 

I think you have explained it well and I agree with your comments.

 

With regards to using Google Earth..... I note you are located somewhere on the South Coast..... Take the roundabout in Poole at N 50 42.449 and W 1 55.532... Memory Map OS shows elevation: 108ft and Google Earth shows elevation: 127ft. If you are setting your known elevation with Google Earth, could this be the reason for the discrepancy??? Might not be right, but just a thought....

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Can someone tell me if this is all right please? Sorry if I haven't explained it very well. :)

 

One other question is whether anyone knows a reason why the auto calibration in my 60csx almost always calibrates it about 20ft lower than my correct elevation? I am using google earth to give the correct elevation for my location and a non Garmin topo map on the GPS.

 

I think you have explained it well and I agree with your comments.

 

With regards to using Google Earth..... I note you are located somewhere on the South Coast..... Take the roundabout in Poole at N 50 42.449 and W 1 55.532... Memory Map OS shows elevation: 108ft and Google Earth shows elevation: 127ft. If you are setting your known elevation with Google Earth, could this be the reason for the discrepancy??? Might not be right, but just a thought....

I have tried an experiment for several locations and compared the elevation on the topo map on my GPS (a third party map), the elevation on google earth, and the elevation on the free elevation data on Anquet Maps. I found similar results to what you found. The topo map and google earth always give the same elevation suggesting that they are produced from the same elevation data. I have found out that the topo map is produced from NASA SRTM V2 height data. The elevation from Google earth and the elevation from Anquet Maps are always different but vary by how much. In some locations Google earth is reading 5 or 6 ft higher and in others, it is reading 30 feet higher. This is quite possibly the reason for why the elevations of Google earth do not agree with the GPS auto-calibrated ones. Thanks for that tip. :)

 

In future, I will keep in mind that Google earth elevation is not always as accurate as you might think. :shocked:

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Can someone tell me if this is all right please? Sorry if I haven't explained it very well. :)

 

One other question is whether anyone knows a reason why the auto calibration in my 60csx almost always calibrates it about 20ft lower than my correct elevation? I am using google earth to give the correct elevation for my location and a non Garmin topo map on the GPS.

 

I think you have explained it well and I agree with your comments.

 

With regards to using Google Earth..... I note you are located somewhere on the South Coast..... Take the roundabout in Poole at N 50 42.449 and W 1 55.532... Memory Map OS shows elevation: 108ft and Google Earth shows elevation: 127ft. If you are setting your known elevation with Google Earth, could this be the reason for the discrepancy??? Might not be right, but just a thought....

I have tried an experiment for several locations and compared the elevation on the topo map on my GPS (a third party map), the elevation on google earth, and the elevation on the free elevation data on Anquet Maps. I found similar results to what you found. The topo map and google earth always give the same elevation suggesting that they are produced from the same elevation data. I have found out that the topo map is produced from NASA SRTM V2 height data. The elevation from Google earth and the elevation from Anquet Maps are always different but vary by how much. In some locations Google earth is reading 5 or 6 ft higher and in others, it is reading 30 feet higher. This is quite possibly the reason for why the elevations of Google earth do not agree with the GPS auto-calibrated ones. Thanks for that tip. :)

 

In future, I will keep in mind that Google earth elevation is not always as accurate as you might think. :shocked:

 

No probs.

 

Another interesting thing about the 'inaccuracies' of Google earth is if you download the 'Geocaching Google Earth Viewer' .kml file and try viewing the locations of the geocaches in google earth..... they are somewhat out by their correct location... you might even find some that are on the opposite bank of a river, for example..... ok for a general view, but totally useless in trying to find or plan caches! Always best to use the gpx files and import them into an OS mapping system - I have the full UK OS Discoverer maps 1:50k on my 62s and when I connect it to BaseCamp, the caches show up on the OS map - easy to do a route plan from there.... the only time I use google maps is to look at the street view pictures to see where I can park!

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Another interesting thing about the 'inaccuracies' of Google earth is if you download the 'Geocaching Google Earth Viewer' .kml file and try viewing the locations of the geocaches in google earth..... they are somewhat out by their correct location... you might even find some that are on the opposite bank of a river, for example..... ok for a general view, but totally useless in trying to find or plan caches! Always best to use the gpx files and import them into an OS mapping system - I have the full UK OS Discoverer maps 1:50k on my 62s and when I connect it to BaseCamp, the caches show up on the OS map - easy to do a route plan from there.... the only time I use google maps is to look at the street view pictures to see where I can park!

 

The google earth geocache viewer intentionally obfuscates the location of the caches, it is done by Groundspeak and does not show the inaccuracies of google earth. Drag and drop a PQ into GE and you will see that their locations are reflected accurately.(as accurate as the local image calibration is)

 

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Another interesting thing about the 'inaccuracies' of Google earth is if you download the 'Geocaching Google Earth Viewer' .kml file and try viewing the locations of the geocaches in google earth..... they are somewhat out by their correct location... you might even find some that are on the opposite bank of a river, for example..... ok for a general view, but totally useless in trying to find or plan caches! Always best to use the gpx files and import them into an OS mapping system - I have the full UK OS Discoverer maps 1:50k on my 62s and when I connect it to BaseCamp, the caches show up on the OS map - easy to do a route plan from there.... the only time I use google maps is to look at the street view pictures to see where I can park!

 

The google earth geocache viewer intentionally obfuscates the location of the caches, it is done by Groundspeak and does not show the inaccuracies of google earth. Drag and drop a PQ into GE and you will see that their locations are reflected accurately.(as accurate as the local image calibration is)

 

Thanks for the clarification - good job I put the '' quotes around the word inaccuracies... :-)

 

What is the point of the kml view distortion, if the PQ gpx import shows correct positions? IMO kml view is totally useless.

 

Thanks for bringing to my attention the possibility of importing a gpx into GE - I never knew about it.

 

Cheers.

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What is the point of the kml view distortion, if the PQ gpx import shows correct positions? IMO kml view is totally useless.

 

I believe it's because the KML viewer works without authentication or authorization and so anyone (even without having an account) could view the coordinates of all caches.

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What is the point of the kml view distortion, if the PQ gpx import shows correct positions? IMO kml view is totally useless.

 

I believe it's because the KML viewer works without authentication or authorization and so anyone (even without having an account) could view the coordinates of all caches.

 

Thanks for the reply. Just cannot understand the use of the kml viewer if it shows the wrong locations. I just logged out of the GC site and I cannot find a link to download the kml viewer when logged out??? How does someone view the kml file in GE without an account?

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What is the point of the kml view distortion, if the PQ gpx import shows correct positions? IMO kml view is totally useless.

 

I believe it's because the KML viewer works without authentication or authorization and so anyone (even without having an account) could view the coordinates of all caches.

 

Thanks for the reply. Just cannot understand the use of the kml viewer if it shows the wrong locations. I just logged out of the GC site and I cannot find a link to download the kml viewer when logged out??? How does someone view the kml file in GE without an account?

 

By being emailed it by another GE user?

 

The GE kml is, AFAIK, to be used when route planning or getting an overview of caches in an area, which it does very well - and not for use actually finding a cache - that's what we use our GPSes for (but I could be wrong?) :)

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By being emailed it by another GE user?

Yes, I understand where you are coming from, but this is against the GC.com rules, therefore they wouldnt presumably offset the locations just in case it got emailed about, would they? locations are free even for non premium members - otherwise one could say why not offset the gpx files just in case they got emailed to a non premium member? I'm still not convinced of a true use for the kml GE file.

 

The GE kml is, AFAIK, to be used when route planning or getting an overview of caches in an area, which it does very well - and not for use actually finding a cache - that's what we use our GPSes for (but I could be wrong?) :)

Agree on the kml showing an overview of caches in an area - but for those people without OS mapping on their GPS, I dont agree that it can be used as an accurate route planning tool as such - there are instances where caches are shown on the opposite bank of a river, and the detour road route ( or even nearest footbridge ) could be miles around to get to the other side. The map satellite view seems accurate on the webpages, so I still fail to see why the kml locations are distorted.

 

I just still fail to see the true use of the kml viewer, and the original reason why I mentioned this was to advise a previous poster of its limitations, if they decided to rely on the kml viewer - they had previously used GE to note elevations - which do not tie in with OS maps of the area. Just my opinion - no disrespect intended.

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Yes, I understand where you are coming from, but this is against the GC.com rules, therefore they wouldnt presumably offset the locations just in case it got emailed about, would they? locations are free even for non premium members - otherwise one could say why not offset the gpx files just in case they got emailed to a non premium member? I'm still not convinced of a true use for the kml GE file.

 

a GPX only contains the coordinates of a specific set of caches. The KML doesn't contain any actual coordinates, it merely describes a live, online interface into Groundspeak's cache database. This interface can be used not only from GE, it could also be used from any other application. Since the KML doesn't contain any authentication information, the interface doesn't know who's requesting the coordinates - it could be anyone, from anywhere, using any application. Groundspeak requires you to have an account go view coordinates, but with the KML interface, you don't need one in order to view the caches and see/download their coordinates. That's why they obfuscate them.

 

Something being against the rules doesn't mean that nobody will do it, all the "illegal" mobile applications are the best example for this. Groundspeak wants to protect their data, and a public online interface to all caches' coordinates doesn't do that.

 

But don't get me wrong, this is just an explanation for the "why", it doesn't mean I actually agree with this decision. Personally I find the KML viewer to be pretty useless too.

Edited by dfx
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Yes, I understand where you are coming from, but this is against the GC.com rules, therefore they wouldnt presumably offset the locations just in case it got emailed about, would they? locations are free even for non premium members - otherwise one could say why not offset the gpx files just in case they got emailed to a non premium member? I'm still not convinced of a true use for the kml GE file.

 

a GPX only contains the coordinates of a specific set of caches. The KML doesn't contain any actual coordinates, it merely describes a live, online interface into Groundspeak's cache database. This interface can be used not only from GE, it could also be used from any other application. Since the KML doesn't contain any authentication information, the interface doesn't know who's requesting the coordinates - it could be anyone, from anywhere, using any application. Groundspeak requires you to have an account go view coordinates, but with the KML interface, you don't need one in order to view the caches and see/download their coordinates. That's why they obfuscate them.

 

Something being against the rules doesn't mean that nobody will do it, all the "illegal" mobile applications are the best example for this. Groundspeak wants to protect their data, and a public online interface to all caches' coordinates doesn't do that.

 

But don't get me wrong, this is just an explanation for the "why", it doesn't mean I actually agree with this decision. Personally I find the KML viewer to be pretty useless too.

 

Thanks for the explanation about the online dbase.

 

I'm glad someone else agrees that the kml is pretty useless - thought I was missing something obvious.

 

You would think that with 'wrong' coords and GS wanting to protect their data, that they would just junk the thing and have done with it.

 

Thnaks for getting back to me with the info - appreciated.

 

Steve

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To calibrate it to the correct pressure, you enter the current BAROMETRIC pressure for you location AT SEA LEVEL and then it works out the difference between the ambient pressure that it reads at your location and the barometric pressure at sea level to work out your current altitude (as the pressure difference between altitudes is always the same (unless each altitude is experiencing different weather)). I know that it needs you to enter the pressure at sea level for your current location because it asks for the barometric pressure in the manual and not the ambient pressure. The ambient pressure is the actual pressure at your location and the barometric pressure is calculated sea level pressure using ambient pressure and elevation (explained below).

 

I've got an OR 550T. When I try to enter the barametric pressure, it will only allow me to enter it to one decimal place (If it is 31.14, I can only enter 31.1). But it displays the barametric pressure to two decimal places.

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To calibrate it to the correct pressure, you enter the current BAROMETRIC pressure for you location AT SEA LEVEL and then it works out the difference between the ambient pressure that it reads at your location and the barometric pressure at sea level to work out your current altitude (as the pressure difference between altitudes is always the same (unless each altitude is experiencing different weather)). I know that it needs you to enter the pressure at sea level for your current location because it asks for the barometric pressure in the manual and not the ambient pressure. The ambient pressure is the actual pressure at your location and the barometric pressure is calculated sea level pressure using ambient pressure and elevation (explained below).

 

I've got an OR 550T. When I try to enter the barametric pressure, it will only allow me to enter it to one decimal place (If it is 31.14, I can only enter 31.1). But it displays the barametric pressure to two decimal places.

 

Set it with mbar.

0.1 Hgin = 3.34 mbar, so in effect you would be setting the unit with a resolution of 0.03 Hgin - better than 0.1 resolution.

Maybe this would help?

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This this a great read hope to do some winter camping and geocaching at the same time when i get to my camp site at about 1000 feet up do i Auto my altimeter so i get the right pressure and then i keep an eye on it so if the pressure start to go down then the weather is getting bad and time to leave is that right way on how to read off my 62s

 

want is the best way to read it on my 62s

 

any help would be great

 

thanks

 

LWM

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Calibrate to a known elevation before you start, and then leave AC on.

On the way to camp.....use Variable Elevation setting and Auto Calibration setting.

AC will compensate for the effect of elevation change while hiking.

 

As soon as you arrive in camp, Switch to "Fixed Elevation" for your overnight stay.

 

Any change you see in the Baro Press overnight will be due to actual climate conditions changing.

 

When you leave in the morning, change back to Variable Elevation.

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