Adding Altitude

[+nowimfound]

What are your opinions on adding altitude to cache pages? It could be a new "stat" for our profiles...i.e. Caches Below Sea Level or Caches Above 1000' etc.

[+dfx]

there's no real need to have that added to the cache listings. assuming a cache is placed at or at least near ground level, the altitude can be deducted from the coordinates.

 

exceptions will be caches up trees, caches in caves and similar stuff. i don't think those will have any significant influence on any stats though.

Edited October 15, 2010 by dfx

[+dakboy]

Consumer handheld GPSrs calculate elevation very poorly. Unless Groundspeak had a database matching up coords & elevations, it wouldn't be that valuable.

[+Markwell]

Consumer handheld GPSrs calculate elevation very poorly.

I can vouch for that. In some research I did for tech editing a book, I talked to someone on the Garmin technical team.

 

FOR NON-BAROMETRIC ALTIMETERS, because of the angles that the satellites use (based on the distances from the GPS units), they are very narrow angles. These narrow angles give a much wider ranges of proximity to ground. The problem is that if to get a wide enough angle to computer a more accurate altitude, the GPS needs the satellites to be closer to the horizon. If the sats are closer to the horizon, the signal is degraded by the thicker layers of atmosphere - and the accuracy is ruined. So they're in a Catch 22 with accurate altitudes.

 

FOR BAROMETRIC ALTIMETERS ON GPS UNITS, these mirror the altimeters on airplanes. My private pilot buddy showed me how his barometric altimeter was calibrated (a little dial like on the back of a clock) because you needed to listen to the airport status at that time of day to get the barometric pressure offset for the known altitude. The altitude of the runway was a known altitude above sea level, but based on the barometric pressure of the day, you'd have to adjust for the highs and lows (even by the hour).

 

In our area, the topo maps say that everything is around 637 feet above sea level - and we're VERY flat. Adding 6-8 feet to that might indicate that it's up a tree, but then again a mile west of my house is 649 feet elevation. You'd be hard pressed to see the difference.

==================

 

If I've lost you at this point, the consider this: Most GPS units can't get within 30 feet, the altitude could be off by 30 feet, which is pretty significant if you're trying to tell someone it's in the tree top.

[+Don_J]

Consumer handheld GPSrs calculate elevation very poorly.

I can vouch for that. In some research I did for tech editing a book, I talked to someone on the Garmin technical team.

 

FOR NON-BAROMETRIC ALTIMETERS, because of the angles that the satellites use (based on the distances from the GPS units), they are very narrow angles. These narrow angles give a much wider ranges of proximity to ground. The problem is that if to get a wide enough angle to computer a more accurate altitude, the GPS needs the satellites to be closer to the horizon. If the sats are closer to the horizon, the signal is degraded by the thicker layers of atmosphere - and the accuracy is ruined. So they're in a Catch 22 with accurate altitudes.

 

FOR BAROMETRIC ALTIMETERS ON GPS UNITS, these mirror the altimeters on airplanes. My private pilot buddy showed me how his barometric altimeter was calibrated (a little dial like on the back of a clock) because you needed to listen to the airport status at that time of day to get the barometric pressure offset for the known altitude. The altitude of the runway was a known altitude above sea level, but based on the barometric pressure of the day, you'd have to adjust for the highs and lows (even by the hour).

 

In our area, the topo maps say that everything is around 637 feet above sea level - and we're VERY flat. Adding 6-8 feet to that might indicate that it's up a tree, but then again a mile west of my house is 649 feet elevation. You'd be hard pressed to see the difference.

==================

 

If I've lost you at this point, the consider this: Most GPS units can't get within 30 feet, the altitude could be off by 30 feet, which is pretty significant if you're trying to tell someone it's in the tree top.

 

I have a 60CS and have done loop hikes that find my car 100' higher than where I parked it.

[+tomfuller & Quill]

What are your opinions on adding altitude to cache pages? It could be a new "stat" for our profiles...i.e. Caches Below Sea Level or Caches Above 1000' etc.

The highest physical cache in Oregon is: GC1EC8C 9733-Steens Mountain The elevation is 9733' above sea level. I am hoping to be able to visit this one next year.

I have logged several caches above 8000'. I have also logged the virtual in Death Valley which is 282 feet below sea level. My Magellan read 0 feet there. I am told that Garmins will read below sea level.

If you want to put a cache at the top of a mountain, you can compare with the nearest USGS benchmark.

[+MontyFam]

 

I have a 60CS and have done loop hikes that find my car 100' higher than where I parked it.

 

Wowza, did you park it on the sleeping head of a brontasauras?

[+Avernar]

What are your opinions on adding altitude to cache pages? It could be a new "stat" for our profiles...i.e. Caches Below Sea Level or Caches Above 1000' etc.

I wouldn't trust people to put in the correct altitude. If you want the altitude statistics take a look at the FindStatGen GSAK macro.

[+Don_J]

 

I have a 60CS and have done loop hikes that find my car 100' higher than where I parked it.

 

Wowza, did you park it on the sleeping head of a brontasauras?

 

My CS does the same thing. I can do a loop and find that my car is at a higher elevation from where I parked it.

[+DragonsWest]

I've been on hikes where cachers compare elevation registered on their GPSrs - it is not hard to find a 200 ft variance between all units.

 

Take whatever your GPSr is telling you with a granule of salt.

[+Don_J]

What are your opinions on adding altitude to cache pages? It could be a new "stat" for our profiles...i.e. Caches Below Sea Level or Caches Above 1000' etc.

I wouldn't trust people to put in the correct altitude. If you want the altitude statistics take a look at the FindStatGen GSAK macro.

 

We have two caches in a local state park that are 20' apart. One is 400' above the other, and unless you are Spiderman, it will take a half hour of hiking to go from one to the other.

Edited October 15, 2010 by Don_J

[+nowimfound]

All great inputs. Indeed, my GPSr gives odd altitude readings. I've noticed this in the couple of benchmarks I've found. I would guess Groundspeak would have to add it to the cache page via some data base. Thanks for the input on the highest elevation cache!

[+TerraViators]

What are your opinions on adding altitude to cache pages? It could be a new "stat" for our profiles...i.e. Caches Below Sea Level or Caches Above 1000' etc.

I wouldn't trust people to put in the correct altitude. If you want the altitude statistics take a look at the FindStatGen GSAK macro.

 

We have two caches in a local state park that are 20' apart. One is 400' above the other, and unless you are Spiderman, it will take a half hour of hiking to go from one to the other.

Wow!

[+GeoGeeBee]

 

We have two caches in a local state park that are 20' apart. One is 400' above the other, and unless you are Spiderman, it will take a half hour of hiking to go from one to the other.

 

How did that get approved?

[+dakboy]

 

We have two caches in a local state park that are 20' apart. One is 400' above the other, and unless you are Spiderman, it will take a half hour of hiking to go from one to the other.

 

How did that get approved?

Significant barrier to traverse in getting from one to the other. Similar to seeing 2 caches on opposite sides of a 300-foot wide river, with the only crossings being bridges a half-mile away in either direction.

[Andronicus]

 

We have two caches in a local state park that are 20' apart. One is 400' above the other, and unless you are Spiderman, it will take a half hour of hiking to go from one to the other.

 

How did that get approved?

Significant barrier to traverse in getting from one to the other. Similar to seeing 2 caches on opposite sides of a 300-foot wide river, with the only crossings being bridges a half-mile away in either direction.

Or, more likely a earthcache and a traditional.

 

I think elevation would be cool. I don't think it would help in finding a cache, but would give a cool statistic. When doing resurch on wikipedia, I had found that the theoretical accuracy of elevation (on a GPS) is either 1.3 or 1.5 times worse than the horizontal accuracy. Doing benchmark testing, I usualy find that my GPS is within 5m, but sometimes as bad as 16m.

Edited October 18, 2010 by Andronicus

[+dfx]

Or, more likely a earthcache and a traditional.

not necessarily. back in the day, reviewers were much more willing to make exceptions like that.

[+boda]

We went for a ballon ride with our caching partners a few years ago. As we were floating over the orange and grapefruit groves, the balloon pilot took out his older model GPS and pushed a few buttons. We asked if he was checking our altitude and he said that he was just playing with it because the altitude is not accurate. Our caching partner pulled out his GPS and said, "Let's see how close we are." The two were about 100 feet off. I then pulled my identical GPS out and found that I was in between their readings.

 

We are consistentlly off, even when we sometimes calibrate at the same location.

[+geodarts]

I once tried to convince an earthcache owner that allowing only a 25 foot variance between his gpsr elevation reading and the answer that peopke submit for rhe task (record the elevation with your gpsr) made no sense given the wide range in units (from iphones to handhelds) and was not even within the margin of error for his particular unit. I did not succeed in convincing him, although I think I was right.

[+Team GPSaxophone]

Ho hum, every cache in Colorado is over 3315' in elevation. I don't think your idea gives anyone much of a challenge. Except maybe Floridians.

[+Castle Mischief]

What are your opinions on adding altitude to cache pages? It could be a new "stat" for our profiles...i.e. Caches Below Sea Level or Caches Above 1000' etc.

I wouldn't trust people to put in the correct altitude. If you want the altitude statistics take a look at the FindStatGen GSAK macro.

 

How does a GSAK macro collect information on something that's not part of the .gpx file in the first place?

[+ironman114]

Ho hum, every cache in Colorado is over 3315' in elevation. I don't think your idea gives anyone much of a challenge. Except maybe Floridians.

 

I was just thinking the same thing. My mom grew up in Colorado and lived in the San Luis valley @ 7,500' elevation. It is very flat there.

[+dfx]

How does a GSAK macro collect information on something that's not part of the .gpx file in the first place?

 

the same way your GPSr knows the elevation of any random spot you pick off the map.

[+Sol seaker]

If it were to work it would be a great idea.

 

There have been a number of places I've looked for a cache where altitude was everything. They were on hills. The coords read the same at the top and at the bottom (straight down, cliff). It would have been nice not to have had to search at the top and at the bottom. There have only been 50 ft - 100 ft differences in altitude.

 

When I was driving over the Cascade Mtns here last summer, I was watching my altimeter in my GPS. As I went up one side of the pass and down the other, it was doing crazy things that at one point was 1000 feet off. Anything this inaccurate surely won't help a at a 50 foot drop.

[+fizzymagic]

How does a GSAK macro collect information on something that's not part of the .gpx file in the first place?

the same way your GPSr knows the elevation of any random spot you pick off the map.

Except your GPSr does not know the elevation of any random point to very good accuracy, as it probably uses only an approximate Digital Elevation Model (DEM).

 

The correct answer is that the GSAK macro uses a web service that returns the ground elevation for the cache coordinates. In the continental US, the USGS is returned on a 10-meter grid horizontally (you get the average elevation of approximately a 10-m square centered on the point). Many areas of the US are on a 3-m grid, which gives quite good elevations. Worldwide, there is a 30 m grid that was done from satellites via radar ranging.

 

I agree that the elevations of your finds are a fun statistic.

[+NYPaddleCacher]

How does a GSAK macro collect information on something that's not part of the .gpx file in the first place?

 

the same way your GPSr knows the elevation of any random spot you pick off the map.

 

That's two different things. I GPSr might know (or at least provide a reasonable estimate) of the elevation but unless in encodes that information into a gpx file GSAK isn't going to able to display it. The elevation or altitude is not encoded into the coordinates as was suggested earlier.