DEM : filling holes manually

[markbin]

Hi, I am making a route that runs trough canyons (Copper canyon railway Mexico). 3 arc DEM's have, outside the problem that they are inaccurate for canyons, a lot of holes in that area. Those holes are approximately 200m by 200m. Automatic interpolation fills the holes but levels everything still more. Is there a method to manually add the missing points (approximately 10-20 per hole ), before generating the terrain ,so that a smooth terrain can be obtained ?

 

[Jerker]

G'day markbin,

You don't describe the method you use to 'automatically' interpolate the holes in your DEMs (or for that matter, how you create them), so I do not know if the advice I will give will be of any help to you. Firstly I use one of two methods to create the DEMs I need to create. One of those is TransDEM, the other is a variation of the Wewain method using Global Mapper in lieu of MicroDEM and HOG. Both of these have built in 'interpolation' functions, neither of which I use. I utilise the free version of a program called SRTMfill available from www.3dnature.com, which I find easily an excellent example of it's type, which I impose upon the SRTM data before it gets used in either of the above processes. I would, however, suggest that (given the work involved in the rest of the program), "the good doctor's" interpolation routine (based on the T. I. N. process, as it is), would be as good as any other around.

Jerker {}

 

[markbin]

Hi
i have used microdem and hog before , but for this layout i am using mapmaker ;
i have tried different fill utilities , also SRTMfill .
The problem is that there are to much holes , that some are to large , and that the terrain ( narrow canyon ) has to much hight differences. The result with SRTMfill is that you get, at some places , wide valeys instead of narrow canyons ,and at other places , no canyon at all ; just a high wall .
Thats why i was looking for a method to change the data manually , a big job , but still a lot easiers than creating the missing or not fitting mountains by hand.

 

[geophil]

The SRTM 3" holes for Copper Canyon are significant, IIRC. The canyon bottom is missing for miles. These huge gaps may be far enough from the railway at most places. At Divisadero, though, you would be able to look down into the canyon from the station/depot. I don't think any automatic interpolation would be able to fill those big holes with a satisfying result. The TransDEM algorithm is different to the one in MicroDEM and the one in SRTMfill. I wasn't happy with either of them and thus developed my own. However, my automatic method will definitely fail for the larger holes but should work for the smaller ones.

As Jerker has mentioned, there is also the TIN algorithm in TransDEM but for proper terrain you would need a topographic map to trace contour lines. You could, of course, create a somewhat fictitious landscape via TIN without the need for a topo map.