Most accurate Altimeter...

Check this out Fred, even right when the current pressure is calibrated, they don't expect better than 75' accuracy. Then as pressure drifts due to weather it just gets worse.

Fred @ Bison Tactical said:

Ok, I have tried a lot of them, and researched a bunch. I am looking for first hand info from people who use them....

The rules:
a. can't have GPS mapping, or display coordinates
b. has to be accurate within 5m +-
c. ideally should be light weight
d. can't include any mapping features at all nor 2 way communication capabilities (like a phone for example)

The backstory - I compete in an Adventure Race where we can't use GPS navigational aides. I really need a useful altimeter to help determine my position on a topo map compared to real life. I have run a Casio Pathfinder and Suunto Core but both are not accurate enough to provide good Alititude with changing weather conditions, so I am looking for other suggestions (or a suggestion about how to get the two above units to work better).

In prior races I have re-calibrated the altimeter at a known point, but by the time I found the next point (2-3 KM away and +- elevation) it was already incorrect and not giving me good elevation

Click to expand...

And one of these


So you can listen to the AWOS freq from airports near you for the QNH

What you are asking is basically not possible. High and low pressure systems and even big changes in temperature (the heat low, for example) will cause your altimeter to be ”off” without a way to constantly reset it to a known altitude.…either by being at a known location on the map and setting the altitude or by calling the local airport and getting the local altimeter setting (depending on what kind of “setting” capability your equipment has…a kollsman window or the digital equivalent).

What you have done in the past is about as good as it gets for pressure based altimetry.

Use old school
Use your topographic map. Recognise in the map and field a minimum of 2 or 3 different locations and triangulate them with the most possible precision. Use as many reference points as possible to read in the map and field.

Complement that with info from a good altimeter. Zero it frequently at known altitude places and live with the deviation it will give you at different locations and atmospheric conditions.

Check here:

http://www.paragear.com/

Might have something.

Thank you,
MrSmith

Paqueo said:

Use old school
Use your topographic map. Recognise in the map and field a minimum of 2 or 3 different locations and triangulate them with the most possible precision. Use as many reference points as possible to read in the map and field.

Complement that with info from a good altimeter. Zero it frequently at known altitude places and live with the deviation it will give you at different locations and atmospheric conditions.

Click to expand...

This. Learn how to re-section using a lensatic compass, and terrain association.

OREGUN said:

What you are asking is basically not possible. High and low pressure systems and even big changes in temperature (the heat low, for example) will cause your altimeter to be ”off” without a way to constantly reset it to a known altitude.…either by being at a known location on the map and setting the altitude or by calling the local airport and getting the local altimeter setting (depending on what kind of “setting” capability your equipment has…a kollsman window or the digital equivalent).

What you have done in the past is about as good as it gets for pressure based altimetry.

Click to expand...

What Oregun said is exactly correct, I have spent a fair amount of time working the problem when I ran the technical side of an unmanned air vehicle (Lockheed's Desert Hawk)

If you could use GPS and DTED data (at the right level) you could get elevation that accurate, straight GPS alone is not accurate in elevation to give you +/- 5 m in elevation.

MrSmith said:

Check here:

http://www.paragear.com/

Might have something.

Thank you,
MrSmith

Click to expand...

I know the skydiver in the group...

Yep unfortunately it's trying to beat physics, because pressure will change not just with altitude but weather fronts. The altimeter struggles to know what is causing the pressure changes. Even GPS altitude is not great, based on various datums they all have various error, as terrain gets higher relief, positional based GPS error gets worse. I've seen older USGS topo maps be off 25-50m to USGS survey markers in high relief areas. You'd need LIDAR based 3D data that has been calibrated to a known standard and a GPS to get reliable elevation.

USGS topo maps accuracy standard is 90% of points are within 50% of the isopleth elevation delta. Most 7.5 minute maps have 10' contours so 90% of the map should be +/- 5'. You might be better off if there are LIDAR maps available of the area and doing relational positioning based on the enhanced terrain detail they offer. Another other option I've used in the field before is overlaying topo lines on a satellite image. It's usually much easier to visually locate things on them. If you've ever looked at a lot of the 3D elevation sources most are pretty poor for actually providing fine terrain detail, DTED 0, 1, 2 show almost no fine detail, DTED 2 only has an elevation value every 30m. Most USGS 7.5 minute topo maps were made with DTED 1 elevation data, so an elevation point measurement every 90m and everything between is interpolated.

https://www.mission-planning.com/DTED_Part5.htm a good display of various DTED levels, the first one is what most Topo maps are made with.

If you knew the elevation of various landmarks in the area you could back out your positional elevation. We used to do a lot of navigation and geological mapping in the field and something like a Brunton GeoTransit can back that info out, and while amazingly accurate in skilled hands for an overgrown pocket compass, I'm not sure it would do +/-5m.

NiteQwill said:

I know the skydiver in the group...

Click to expand...

I've forgotten more than I ever knew. My last jumps were on a Para Plane Cloud modified by my girlfriend. She happened to have a sewing machine.

As to altimeters, we always reset to 0 as we got on the plane. Every time. And we were only concerned about hundreds of feet. Well, except for those last few.

Thank you,
MrSmith

ToddM said:

Yep unfortunately it's trying to beat physics, because pressure will change not just with altitude but weather fronts. The altimeter struggles to know what is causing the pressure changes. Even GPS altitude is not great, based on various datums they all have various error, as terrain gets higher relief, positional based GPS error gets worse. I've seen older USGS topo maps be off 25-50m to USGS survey markers in high relief areas. You'd need LIDAR based 3D data that has been calibrated to a known standard and a GPS to get reliable elevation.

USGS topo maps accuracy standard is 90% of points are within 50% of the isopleth elevation delta. Most 7.5 minute maps have 10' contours so 90% of the map should be +/- 5'. You might be better off if there are LIDAR maps available of the area and doing relational positioning based on the enhanced terrain detail they offer. Another other option I've used in the field before is overlaying topo lines on a satellite image. It's usually much easier to visually locate things on them. If you've ever looked at a lot of the 3D elevation sources most are pretty poor for actually providing fine terrain detail, DTED 0, 1, 2 show almost no fine detail, DTED 2 only has an elevation value every 30m. Most USGS 7.5 minute topo maps were made with DTED 1 elevation data, so an elevation point measurement every 90m and everything between is interpolated.

https://www.mission-planning.com/DTED_Part5.htm a good display of various DTED levels, the first one is what most Topo maps are made with.

If you knew the elevation of various landmarks in the area you could back out your positional elevation. We used to do a lot of navigation and geological mapping in the field and something like a Brunton GeoTransit can back that info out, and while amazingly accurate in skilled hands for an overgrown pocket compass, I'm not sure it would do +/-5m.

Click to expand...

Nice explanation.

Most accurate....probably not.

Revue Thommen Altimark from 1988.





Shitty crystal movement but the altimeter was cool tech for its day.

I used it with topo maps hiking the Jura where France an de Switzerland put an altitude on everything that is of importance.