Which is the correct elevation gain for a trail?

Question

Hello,

I am trying to get an elevation profile for a trail, 100 miles long. I used CalTopo, Trail Forks, ArcGIS Pro, Ride with GPS and each one is wildly different from the other, especially the amount of elevation gain over the whole route. I used UTM Zone 11 ( I am on the North Eastern end of California), and lidar to get the numbers on ArcGIS pro.

How would I know which one is the most accurate? ArcGIS seems like it is the most inaccurate as it differs the most from the other three. Could this be because I am ran the tool incorrectly?

I look forward to any input you have, thanks!

ThomasHoman · Answer

Hi Michelle,

Check out - https://support.esri.com/en-us/knowledge-base/how-to-determine-elevation-along-a-line-feature-at-a-sp-000022900

If you have the lidar as a surface in your map you can take the trail, add points along the line then determine elevation where the point intersects your surface. I might miss so highs or lows but if you set the point interval tight enough those will be picked up.

MichelleAbramson · Answer

Hi,

That kinda gets at my main issue. I don't know a lot of the specifics for any of the apps, but they are all fairly similar to each other. All I know is that RideGPS and Trail Forks are based on rider collected data while CalTopo was given a GPX file. I don't know their basemap, elevation data etc. I agree that means I can rely on the GIS data the most, but the number seems wrong.

I dont know where the Lidar came from, it was from the previous GIS manager. I have another source to get Lidar from a single source so I will do that, thank you for the advice!

The other thing i noticed is that when I pulled the elevation gain from ArcGIS it just subtracted the highest elevation from the lowest elevation, but as its a trail that is not entirely accurate as there is climbs and descents along the trail. I manually did this last time, but is there any way to automate this calculation using the GIS tool?

Thank you in advance!

ThomasHoman · Answer

Can you provide specifics? There is a whole bucket of questions that would need to be answered to provide context such as date of collection, completeness, expected data quality/granularity, equipment, many others, etc... Proving data quality can be a huge rabbit hole to drop into.

My personal thought is that if the Lidar was collected in a single project with quality reports available, I would trust that the most since lidar is direct measurement. If the lidar came from multiple projects over years the accuracy would be a bit more suspect.

Cheers!

Tom