[Gdal-dev] Merging Dems

[Chris Pennock]

Todd,

Thanks for the reply. I should have said that I *am*
using gdal_merge to merge the dems. The problem is
that I am warping them before the merge, which
"rounds" the edges of the dem, making it hard to fill
the gaps later.

Unless you're implying that I should just use
gdal_merge on the dems directly... but then I can't
specify the resolution I need with a nice resampling
algorithm like -rcs. Furthermore, merging dems
directly introduces some oddly shaped gaps between
dems that led me to believe that it was the "wrong
way" to do things.

How do you typically merge dems into one large
heightmap?

Thanks for the pointer to those dem utils!

Chris

--- Todd Fagin <tfagin at coordinatesolutions.com> wrote:

> GDAL_MERGE is probably the way to go to merge the
> DEMs.  Recently, though, I
> found this site, which has some nifty DEM tools for
> GDAL:
> 
>  
> 
> http://www.perrygeo.net/wordpress/?p=7
> 
>  
> 
> Todd Fagin
> 
>  
> 
>  
> 
>  
> 
>  
> 
> -----Original Message-----
> From: gdal-dev-bounces at lists.maptools.org
> [mailto:gdal-dev-bounces at lists.maptools.org] On
> Behalf Of Chris Pennock
> Sent: Tuesday, June 20, 2006 2:02 PM
> To: gdal-dev at lists.maptools.org
> Subject: [Gdal-dev] Merging Dems
> 
>  
> 
> Hi all,
> 
>  
> 
> Merging dems seems like a common task, but I
> 
> cannot find a way to do it well using gdal. Is there
> a
> 
> best practice I should be aware of?
> 
>  
> 
> I realize that there will always be gaps between
> dems,
> 
> which must be fixed afterward (thanks Craig and
> Ben),
> 
> but what is the best way to merge the dems together,
> 
> with "clean" NODATA edges, so that the gaps can
> 
> be filled?
> 
>  
> 
> The problem I run into is that warping with "-rcs"
> for
> 
> cubic spline resampling, which looks best, leaves
> the
> 
> edges of the dem "rounded off". E.g. if the data
> 
> should be:
> 
>  
> 
> 1000, 1000, 1000, NODATA, NODATA
> 
>  
> 
> I get instead:
> 
>  
> 
> 1000, 1000, -400, -5000, NODATA
> 
>  
> 
> And so I don't have clean cut offs from data to
> 
> NODATA, which makes gap filling challenging.
> 
>  
> 
>  
> 
>  
> 
> Any help would be much appreciated.
> 
>  
> 
> Thanks,
> 
> Chris
> 
>  
> 
> __________________________________________________
> 
> Do You Yahoo!?
> 
> Tired of spam?  Yahoo! Mail has the best spam
> protection around 
> 
> http://mail.yahoo.com 
> 
> _______________________________________________
> 
> Gdal-dev mailing list
> 
> Gdal-dev at lists.maptools.org
> 
> http://lists.maptools.org/mailman/listinfo/gdal-dev
> 
> 


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com