[gdal-dev] Aster tif files to hgt

Scott Arko saarko at alaska.edu
Wed Nov 9 21:47:11 EST 2011

Hi Mira,

I suspect you are finding what many have, that there are some artifacts in
the ASTER GDEM that make it not well suited to certain applications.
 Having blunders that are 1500m higher than true is a bit unusual in my use
of this data set, but probably not unheard of.  But, as you say it does not
have the holes that you will have to deal with using SRTM.  You may find
that the best option is to use ASTER GDEM to fill the holes in your SRTM
data.  This should be possible and you can perhaps even use gdalmerge.py to
accomplish this.  Just make sure you set the nodata value properly and that
your SRTM DEM is the last file that you merge.  This should place the GDEM
down first and then the SRTM data on top of it.  If you have your nodata
value set properly, then the GDEM will fill the holes of the SRTM.  I'm not
certain this will work, but is worth a try.  There are more rigorous ways
of combining data sets, but this should give you an excellent indication of
whether this approach is feasible at all.


On Wed, Nov 9, 2011 at 5:31 PM, Jaromír Mikeš <mira.mikes at seznam.cz> wrote:

> > Od: Scott Arko <saarko at alaska.edu>
> Hello Scott,
> > I wouldn't worry about it the files look identical and the file is
> working
> > in your application.  If you have a program that can load both formats
> you
> > should be able to do a direct comparison to see if there is a shift.
> Actually I don't have a program to compare GeoTIFF and my hgt file at the
> moment.
> > At most, it sounds like the shift you would encounter is 1/2 pixel or
> about 15
> > meters.
> 15m is not issue for me. I haven't idea how big shift it can be.
> >I would try the files in your application and see if the results
> > look reasonable.
> I made comparison between map build from original SRTM files and map build
> from files I converted from Aster.
> Aster based map
> pros
> * there are not holes at all for my area.
> cons
> * there are contours in sea ( they are not on original SRTM) 20m 40m.
> there is not too much places like this, but they are.
> * there are peaks in some areas which shouldn't be there
> they are on places where SRTM having holes, but some most SRTM holes are
> covered well by ASTER
> Some of the peaks are over 4000m but there is highest point about 2600m in
> this area.
> ---------------------------------
> Is it possible remove at least some of these artifacts?
> e.g. setting threshold for highest point on map?
> regards
> mira

Scott Arko
Alaska Satellite Facility Deputy Director
University of Alaska Fairbanks

903 Koyukuk Drive
Fairbanks, AK 99775
Phone: (907) 474 - 5570
email:  saarko at alaska.edu
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