Elevation Profile Horizontal Distance Wrong?

[CDTCAdministrator]

I'm creating elevation profiles to update some pre-existing trail maps in a very mountainous region of the US. I've been using the "Ready to Use" Profile tool successfully, but just realized that the horizontal distance of at least one of the segments is coming out very different than the distance from the Calculate Geometry tool (off by ~2.5 miles). I have tried using a variety of different tools (the interactive Profile tool, and Interpolate Shape)  to create the elevation profiles, and everything is getting the same horizontal distance for the segment -- which is still off from the calculated distance. I've also tried things like reprojecting the segment line and even moving it (using the editing tools) thousands of miles to see if  that makes any difference, and the behavior is the same. I'm at a loss to explain this, and would appreciate any insight that can be shared! 

There are no error messages or even warnings coming up doing any of this. For reference, I'm using ArcPro 2.8.1. 

[Scott_Harris]

When using Calculate Geometry, which "length" geometry attribute are you choosing?

[CDTCAdministrator]

Thanks for responding!

I've tried it with both LENGTH and LENGTH_GEODESIC, and they only differ by ~0.01 mile (as opposed to the nearly 3 miles I'm seeing with the elevation profile). I've also tried doing each with different projections to make sure there isn't some underlying projection issue. LENGTH_3D has never been an option. 

[Scott_Harris]

My best guess: there is a geometry problem with the particular line (see https://pro.arcgis.com/en/pro-app/2.8/tool-reference/data-management/checking-and-repairing-geometri...)

[CDTCAdministrator]

@Scott_Harris I appreciate your help and thoughts. The Check Geometry tool isn't finding anything, but it is reassuring to hear that it sounds like there is a problem somewhere with the data (and not me just totally misunderstanding, for years, how elevation profile horizontal distances work). I will see about recreating the line from a much earlier step and hope that fixes the issue. 

[GeologyAdmin]

My thought is that your elevation surface doesn't cover the whole length of your line. If that happens the profile starts/ends where the surface does. Perhaps try editing the line so that it doesn't extend off your elevation surface.