Gaia GPS Collaboration Thread

[DanInDenver]

Datums I'm stumped. Does it really matter?

Down a rabbit hole as work is slow. So I read up on the 10th Mountain Huts. A page on there on GPS and how not to rely just on GPS got me thinking. Topic of datums matching between your map and your GPS and how if they don't you could be off 200 meters or more.
https://www.huts.org/In_The_Field/gps_info.php

GAIA has datum settings for WGS84 and NAD27. There is no setting for NAD83. There are comments in the help section of GAIA requesting that they have an NAD83 setting as recent as 5 months ago but no official response.

All my MVUM's are NAD83. So if I load my MVUM in NAD83 and GAIA is set for WGS84 and my Dual GPS is feeding position data in WGS84 will my position show accurately on the map? My hunch is pretty darn close and I wont drive into a lake.

What happens when the above scenario but using an NAD27 map. I think here is where the opportunity for greater error could occur. But if I change the setting in GAIA to NAD27, even though data is coming in as WGS84 GAIA will do the conversion and correctly plot me on the loaded NAD27 map?

I am not marking property or land boundaries or building roads but certainly would like to know accurately where I am and of course understand how I should be using the tools at my disposal. Next time out I would like to try more map and compass use and use the GPS to validate I know what I am doing. I think a class in good old orienteering may be beneficial.

 

[DaveInDenver]

USFS topo maps are usually NAD27 and WGS83 what your GPS position is based upon. OpenStreetMap is projected in WGS84. Most GPS receivers can transform your position in several datums.

The map is projected on whatever datum it is, that can't be changed without converting and rebuilding the map.

You'd only really need NAD83 if you're collecting primary data for new maps, e.g. you're in GIS or something. The majority of the time you only need WGS84 and NAD27 to match to whatever map you're using.

If you have an MVUM in NAD83 you'd probably want to use NAD27. They aren't strictly related other than the U.S. Government trying to accurately project North America. As a result there's a standard transformation defined for it called NADCON (go to NCAT to see the transform).

 

[DouglasVB]

FWIW, I'm involved with Trails Off Road. There is pretty good coverage in Colorado (381 trails in the database currently for Colorado) and with more trails being added all the time. Could be another good source for folks looking for trail and route info https://www.trailsoffroad.com/

At least a couple Rising Sun members or alumni are also part of the mapping team at Trails Off Road.

In addition to the trail guides, you can also get detailed GPX files to load into Gaia, another iProduct or Android app, or into a regular GPS.

The free tier of membership gets you quite a bit of info. The paid membership is like $25/year and gets you a lot more details and some bonus trails.

 

[Stuckinthe80s]

Definitely good to know! While I'm enjoying creating my own routes, it sure is nice to follow someone else's .gpx when it's available.

 

[DaveInDenver]

Was reading something this morning @DanInDenver. Not sure if you're a ham or not nor whether APRS is on your radar, but APRS positions are assumed to be WGS84 unless otherwise indicated.

http://www.aprs.org/datum.txt

So your position and positions of other APRS stations may in theory mismatch on topo maps projected in NAD27 or NAD83 and you don't "otherwise indicate", which means using the "DATUM" keyword in the comment section of your packets and having that parsed in software.

Your basic position is still valid in WGS84 in the standard position fields, so existing clients would still see your location with any inherent error even if you include alternate datum position.

ETA: I think there may actually be chance of an error if you do use NAD27 (for example) position in the comment field due to (I presume) generating NAD27 positions. That would depend on what format you set your GPS receiver to output or your hardware/software configuration (perhaps you have two receivers, a box generating transformed data, etc.). Point being APRS assumes WGS84 and clients will place your position based on that when decoding packets.

 

[Stuckinthe80s]

Datums I'm stumped. Does it really matter?

Down a rabbit hole as work is slow. So I read up on the 10th Mountain Huts. A page on there on GPS and how not to rely just on GPS got me thinking. Topic of datums matching between your map and your GPS and how if they don't you could be off 200 meters or more.
https://www.huts.org/In_The_Field/gps_info.php

GAIA has datum settings for WGS84 and NAD27. There is no setting for NAD83. There are comments in the help section of GAIA requesting that they have an NAD83 setting as recent as 5 months ago but no official response.

All my MVUM's are NAD83. So if I load my MVUM in NAD83 and GAIA is set for WGS84 and my Dual GPS is feeding position data in WGS84 will my position show accurately on the map? My hunch is pretty darn close and I wont drive into a lake.

What happens when the above scenario but using an NAD27 map. I think here is where the opportunity for greater error could occur. But if I change the setting in GAIA to NAD27, even though data is coming in as WGS84 GAIA will do the conversion and correctly plot me on the loaded NAD27 map?

I am not marking property or land boundaries or building roads but certainly would like to know accurately where I am and of course understand how I should be using the tools at my disposal. Next time out I would like to try more map and compass use and use the GPS to validate I know what I am doing. I think a class in good old orienteering may be beneficial.

A guide to basic orienteering is something I've been thinking about for a while. I learned all of it when I was a kid and became fairly proficient at it tromping through the Ozarks. However, I haven't used it in at least 25 years and I'm super rusty.

After I become reacquainted with the art, I'm going to try to do a class sometime this summer with the help of some folks who are more proficient than me. While I love geeking out on gps technology, I recognize that most of us are becoming WAY too reliant on it and think orienteering is just as valuable of a skillset to our community as recovery skills and basic first aid. The more we can all help each other become proficient in these skills, the better off we'll all be!

 

[DaveInDenver]

At least a couple Rising Sun members or alumni are also part of the mapping team at Trails Off Road.

Speaking of teams, is there a Rising Sun team set up Nic (@Stuckinthe80s)? That may require a professional subscription, not sure.

 

[Stuckinthe80s]

Speaking of teams, is there a Rising Sun team set up Nic (@Stuckinthe80s)? That may require a professional subscription, not sure.

Not that I know of. This is definitely worth exploring though.

 

[rover67]

FWIW:

https://blog.gaiagps.com/android-be...ail&utm_campaign=january-newsletter-2-members

new beta version of Gaia.

 

[Mendocino]

I have a Pro version of Gaia and like it a lot. However, I really wish it had APRS integration. APRS integration is a frequent request but Gaia does not seem to be interested in it.

As for reference frames. GPS is in WGS-84 and NAD-27 and NAD-83 are essentially projections from an Earth Centered, Earth Fixed reference (WGS-84), to one that incorporate a better vertical data for the Earth's surface (the Geoid). Going from WGS-84 to NAD-27 or NAD-83 involves a translation, scale and rotation between the two systems (I've simplified this). WGS-84 and NAD-83 are very close to each other horizontally in NA. NAD-27's off a bit bit I never worry about it unless I am using a map and compass for orienteering.

YMMV

 

[DaveInDenver]

Not that I know of. This is definitely worth exploring though.

It appears to set up a Gaia team requires bumping up to the Gaia for Professionals, which is $40 per user per year. It appears targeted for SAR, firefighters, primary land managers.