Hi Mira,<div><br></div><div>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. </div>
<div><br></div><div>Thanks,</div><div>Scott<br><br><div class="gmail_quote">On Wed, Nov 9, 2011 at 5:31 PM, Jaromír Mikeš <span dir="ltr"><<a href="mailto:mira.mikes@seznam.cz">mira.mikes@seznam.cz</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><div class="im">> Od: Scott Arko <<a href="mailto:saarko@alaska.edu">saarko@alaska.edu</a>><br>
<br>
Hello Scott,<br>
<br>
</div><div class="im">> I wouldn't worry about it the files look identical and the file is working<br>
> in your application. If you have a program that can load both formats you<br>
> should be able to do a direct comparison to see if there is a shift.<br>
<br>
</div>Actually I don't have a program to compare GeoTIFF and my hgt file at the moment.<br>
<div class="im"><br>
> At most, it sounds like the shift you would encounter is 1/2 pixel or about 15<br>
> meters.<br>
<br>
</div>15m is not issue for me. I haven't idea how big shift it can be.<br>
<div class="im"><br>
>I would try the files in your application and see if the results<br>
> look reasonable.<br>
<br>
</div>I made comparison between map build from original SRTM files and map build from files I converted from Aster.<br>
<br>
Aster based map<br>
<br>
pros<br>
* there are not holes at all for my area.<br>
<br>
cons<br>
* there are contours in sea ( they are not on original SRTM) 20m 40m.<br>
there is not too much places like this, but they are.<br>
* there are peaks in some areas which shouldn't be there<br>
they are on places where SRTM having holes, but some most SRTM holes are covered well by ASTER<br>
Some of the peaks are over 4000m but there is highest point about 2600m in this area.<br>
<br>
---------------------------------<br>
<br>
Is it possible remove at least some of these artifacts?<br>
e.g. setting threshold for highest point on map?<br>
<br>
regards<br>
<br>
mira<br>
</blockquote></div><br><br clear="all"><div><br></div>-- <br>Scott Arko<br>Alaska Satellite Facility Deputy Director<div>University of Alaska Fairbanks<br><br>903 Koyukuk Drive<br>Fairbanks, AK 99775<br>Phone: (907) 474 - 5570<br>
email: <a href="mailto:saarko@alaska.edu" target="_blank">saarko@alaska.edu</a><br><a href="http://www.asf.alaska.edu/aadn" target="_blank">http://www.asf.alaska.edu/aadn</a></div><br>
</div>