Climbing Analysis DEM warning

[KanyonKris]

I often use the Climbing Analysis tool to add elevation to a hand-drawn track. Seems to work reliably with the auto-download 30m option, but I ran into a problem using DEM data. I traced the route of the Porcupine Rim trail near Moab, Utah. When selecting the DEM dataset in the Climbing Analysis window it warns me that the track covers missing DEM files. So I use the 3D view to look along the whole trail and it falls on good, 3D terrain from the DEM files. The eastern-most point of the trail does come a bit close to the edge of the Rill Creek DEM file and I see the "edge of the world cliff" in 3D mode due to the missing eastern adjacent Warner Lake DEM. So for good measure I download the Warner Lake DEM and now no more "edge of the world cliff" to the east but Climbing Analysis still gives me the missing DEM warning. What could be wrong?

I watch when TF generates the 3D view and it says it's using the DEM files. Is the 3D view a good way to check for complete DEM coverage? The 3D settings window allows the selection of "use DEM files if available" for the data source - does TF drop back to auto-download 30m data if it finds missing DEM data? If so I'd prefer to have another option to force TF to use only DEM data so I can more easily check for areas where DEM data is missing. TF needs to supply more feedback so the user can see where the DEM data is missing.

To explain a bit further, I'd be happy to use the 30m auto-download dataset, but I found it to be quite out of registration with the 2D topo and aerial datasets such that the trail along the edge of the Porcupine Rim dropped off the edge a few times - really messes up the track elevation profile. The DEM data is aligned better (and has higher resolution) - that's why I'm trying to use it for the elevation data (via Climbing Analysis) for the trail track.

(Sorry for the double post. I got an error the first time.)

[Krein]

Hi Kris,

I've just recently encountered this as well.  If a call to "getelevation" returns -32766 TopoFusion considers this value "no DEM."  Sometimes DEM files have small areas with bogus values.

You might get a couple bad values in your track file, but if you open up the GPX in a text editor you can easily find the -32766 "ele" values and change them to something that makes sense.

You'll find that the 30 meter auto-download works better a) with more "model detail" and b) on smaller (geographically) tracks.  If you split the track, for example, so that it downloads DEM data for each half seperately, you might (not sure) find that the track off the cliff problem is better.

Regarding whether TF is downloading or using DEMS, I agree it could be more clear.  Checking the 3D view doesn't guarantee that you don't have a hole somewhere because of resolution issues.  If you knew what area was giving the missing dem value, and zoomed in, re-did a 3D view you would see a big pit.

The code checks the upper left corner of the view area.  If no elevation can be found in DEM, it downloads.  If it encounters "no dem" areas later, it just sets them to a low value, which is why you saw the cliff off the edge of the world when you did have a missing DEM file.

You can also notice that it will list the name(s) of DEM files it is reading.  However, once they are loaded once they are cached, so you won't see the names anymore!

Hope this helps.

[KanyonKris]

I'm still digging into this, but here's a tip that may be helpful to others:

If you suspect bad or missing DEM data, use the Climbing Analysis tool to compute the elevation using the DEM data for your route, then switch to 3D mode and zoom out and tilt the map so you can see under it. The points with bad/no DEM data will "drop through" the map and be way below it with a connector line from the last good point to the first bad point. This will help you see where the bad points are.