Hi all, FYI: I've run a small comparison between ASTER DEM and LIDAR DEMs (say 'true' topography):
http://geomorphometry.org/content/gdem-quick-assessment The 4 case studies can be downloaded from here: http://geomorphometry.org/system/files/GDEM_assessment.zip I'm not too happy with what I've got - GDEM shows very strange patterns in area of low relief and I definitively think that the 30 m resolution is overoptimistic; it should be degraded to 60-90 m (this would enhance the data sharing and save them a lot of trouble). The positional accuracy of GDEM is on the other hand pretty good. GDEM is a frankestein - once you zoom in and add some shading, you can see the stitches, so have this in mind (unlike SRTM DEM which is a complete and a consistent project; but also noisy in many areas). T. Hengl http://home.medewerker.uva.nl/t.hengl/ > -----Original Message----- > From: r-sig-geo-boun...@stat.math.ethz.ch > [mailto:r-sig-geo-boun...@stat.math.ethz.ch] On Behalf > Of Ashton Shortridge > Sent: Friday, November 20, 2009 3:15 PM > To: r-sig-geo@stat.math.ethz.ch > Cc: Yong Li > Subject: Re: [R-sig-Geo] A new ASTER Global DEM data set > > On Friday 20 November 2009 07:09:35 Barry Rowlingson wrote: > > 2009/11/20 Yong Li <yong...@unimelb.edu.au>: > > > Dear all folks, > > > > > > I was informed in the 6th Digital Earth Conference that there is a better > > > place to acquire high resolution of global DEM developed by ASTER, called > > > GDEM with 30 m resolution, and fantastically free of charge. I tried some > > > here (http://www.gdem.aster.ersdac.or.jp/) and it is really better than > > > SRTM if you are outside USA. Hope you will enjoy the free meal. > > > > I just had a look at the tiles near me, and there's quite a bit of > > noise and obvious artefacts - unless there really is a 2000m tower > > about 180m across that I've not noticed in the middle of the > > countryside! > > > > I've not compared with SRTM yet... > > > > Barry > > > > I looked at some here around the North American Great Lakes, and I have to say > I would be very leery about using it in low relief areas. Visually it looked a > lot nicer in the California coastal range, so perhaps less vegetation and > higher relief is important for the sensor. > > That said, it's terrific that alternative global medium-resolution DEMs are > becoming available. Also, I think this ASTER-derived product has captured > higher latitude locations than SRTM (which gets to about 60N and 60S), so it > may be not simply the best but the only choice for many regions. > > Ashton > > > -- > Ashton Shortridge > Associate Professor ash...@msu.edu > Dept of Geography http://www.msu.edu/~ashton > 235 Geography Building ph (517) 432-3561 > Michigan State University fx (517) 432-1671 > > _______________________________________________ > R-sig-Geo mailing list > R-sig-Geo@stat.math.ethz.ch > https://stat.ethz.ch/mailman/listinfo/r-sig-geo _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo