[GRASS-user] Re: [GRASS-dev] question about merging DEMs at the edges

[William Kyngesburye]

I saw something on the list a while back about a delta fill method  
for patching together different DEMs.  I worked out some details for  
using it on large holes in SRTMs when filling with another DEM or  
digitized contours (where the rst fillnulls method doesn't work well)  
and I think I posted it on the user list (or not, nothing in a  
search).  It really works best when what needs to be filled is an  
enclosed area, but the idea might work for edges.

Basically, you take the difference (delta) where they overlap.  Then  
fill the rest of that delta grid, either with a simple linear  
interpolation, or a more complex rst fill.  Linear might work better  
for an edge overlap.  Then add the interpolated delta grid to the  
fill DEM to smoothly bring it in line with the first DEM.  For an  
edge you'd probably want to adjust both grids instead of just the  
filler.

There was a link, ... [digging thru bookmarks] ... can't seem to find  
it ...

Maybe this - it's one of the journal articles:

http://www.asprs.org/publications/pers/2006journal/march/

On Aug 11, 2006, at 2:17 PM, Michael Barton wrote:

> In my project, we are patching together ASTER DEM’s. The ones  
> generated with the new software from USGS are very nice. However,  
> there remain artifacts at the edges. Largely due to the fact that  
> each DEM, in UTM projection, is projected onto the earth’s sphere  
> in slightly different locales, when you patch them together, the  
> edge of one doesn’t exactly match the elevations of the adjacent  
> one. In a few spot tests today, the difference is pretty small <=  
> 15m in elevation. But this is still enough to cause problems in  
> hydrologic modeling if your watershed happens to fall in 2  
> different DEM’s (as ours does).
>
> So does anyone have a suggestion as to how we can smooth out the  
> artificial scarp that occurs when we patch together a couple  
> adjacent DEM’s like this?
>
-----
William Kyngesburye <kyngchaos at kyngchaos.com>
http://www.kyngchaos.com/

"Those people who most want to rule people are, ipso-facto, those  
least suited to do it."

- A rule of the universe, from the HitchHiker's Guide to the Galaxy