TransDEM Forum

I have a good 1.3 arcsec dem of barstow california and just discovered that using google maps at zoom 17 is perfect for making utms to lay track. Anyway with barstow there has always been an issue where the yard curves around the hill.



As you can see the track curves through the edge of the hill and I was wondering is there some way to shift the dem southward slightly offsetting it from the raster maps to adjust it so the track goes around the hill?

The easy answer is just to alter the track or trim a little off the hill in surveyor but I was wondering if the dem and rasters had to be locked?

Maybe you could use a trackplan that is more accurate? Like Open Street Map?
That way you won't have to raise mountains, as fun as it could be.

Cheers Damien

You don't give us a scale in this screenshot (no grid labels) but I would think that one of the two maps here is not accurate.

A "Shift DEM" function exists, but it is meant for DEMs which as a whole were not geo-referenced correctly. Some ASTER DEMs series 1 were such candidates.

There is also the DEM editing tool-kit in TransDEM which is based on the TIN algorithm and Barycentric coordinates, odd math stuff. It's easy to use, though. Tutorials 9 and 11 in the current TransDEM main manual show how.

But first compare the situation with another map from a different source. BTW, some MS Research Maps may have geo-referencing issues.

Not sure how to show scale ( still a newbie) anyway as to using open street map here is what it shows...



Google at least has all 6 tracks that go around the hill and the yard layout is "closer" to real life than the rest but I think this dem is off a hair...

I will try the toolkit, thanks Roland...

The grid labels reveal it all. They are in meters which is very convenient to get an impression on scale. All map projections in TransDEM, wherever they come from, are metric. Th US introduced a metric grid in 1927, the Brits in 1936, ages before the governments dared to confront the people with this odd French measurement units.