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How to fill voids in LIDAR elevation files?

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#1
Simmer

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Hi!

I downloaded some LIDAR elevation files from the following page:
http://usarc.usgs.go...dar_dload.shtml

Unfortunately they are full of voids I'd like to fill. First step was to take a low resolution map around the DEM and feather the edges of the high resolution LIDAR in Global Mapper. After that the LIDAR file merged in more or less but there are still many voids within the area I don't know how to get rid of in Global Mapper (see attached file showing the source).
There seem to be many tools around that can fill voids by interpolation what would be very good for my needs but all tools I could find can only read SRTM HGT files. This raises the question:
If there is no way to interpolate those voids in Global Mapper: Is there any possibility to export high resolution LIDAR data to a HGT file that can be read by those tools?:
http://www.vterrain....Elevation/SRTM/ (see end of page)

Bests,
Simmer

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#2
Michael Schmeling

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Isn't MicroDEM able to read the files and also do the hole filling? I think it should be.
Michael Schmeling
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#3
sitesatlas

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In Global Mapper, you can stack two sources of elevation data on top of each other and the holes in the top DEM are filled by the data in the bottom one. If the data resolution and accuracy aren't similar, you may get some craters and spikes where the holes were, but it might work for your needs. You can export the merged elevation, too.
Michael Borop
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#4
Simmer

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I tried both by now:

Global Mapper:
Yes, there will be quite deep craters where the wholes are. The best available other data for this area (Antarctica) is a DEM with 200 meters resolution. This one here has - I'm not sure - I guess something better than even 1 meter.

Microdem:
At first Microdem couldn't find the holes at all in the file because it assumed that everything between -9999 and the summit is a valid value. I had to resave the GEOtiff in Global Mapper first and then Microdem could read the file properly. Calculate->Elevation->Data voids resulted in:

DEM: TMP.TIF
Holes: 11569716
51.33%


So quite a lot to fill actually. But the only thing I want to get filled are holes within the coverage. The corners I want to merge with the 200m DEM file in Global Mapper which works pretty well.

Unfortunately "none" of the hole file options in Microdem worked for me:
  • Missing data so sealevel: Well that worked, but doesn't make any sense for an area between 2400 and 3600 meters altitude...
  • Fill holes from reference DEM: Used the 200m DEM. No result at all. It looked the same as before.
  • Replace values with reference DEM: No result at all. It looked the same as before.
  • SRTM3 hole fill: No result at all. It looked the same as before.
  • Interpolate across holes: Tried up to a radius of 9999999999 (!) No result at all. It looked the same as before.

Looking at the first one confirms that Microdem does see the holes and knows where to fill them. That makes it so confusing for me to understand why it doesn't do anything in the interpolation process. Would be great if some of you guys can try it with the Mount Erebus file from the first link above.

Bests,
Simmer

#5
François Goulet

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It may not be what you need, but have you tried to convert it to a TIN? With the right parameters, some triangles could fill the voids...

#6
Simmer

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Hello Francois,

How do I convert it to a TIN? I can't find that option in Global Mapper or Microdem.

Bests,
Simmer

#7
François Goulet

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Hello Francois,

How do I convert it to a TIN? I can't find that option in Global Mapper or Microdem.

Bests,
Simmer


It was a shot it the dark... I don't have Microdem or Global Mapper; I work with Arc and MapInfo/Vertical Mapper. I was more asking if you could do it. Sorry if I mislead you, but maybe someone out there could help with this one...

#8
SteveR

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In Microdem you should be able to get rid of the -9999s by using Edit, Mark As Missing, Selected Range; you could enter -1000 for the high and -20000 for the low.

To fill the holes in the DEM using data from another DEM, look up the following topics in Microdem's Help file: "Find Optimal Lag", "SRTM Hole Filling".




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