Hi Holger, I've edited the wiki page, just removed the -dstnodata option to gdalwarp - that works for me!
Cheers Adam ________________________________________ From: Holger Schöner [[email protected]] Sent: 02 October 2009 22:09 To: Adam Ratcliffe Cc: [email protected] Subject: Re: [Mapnik-users] Black holes in hillshade image Hi Adam, On Thu, 1 Oct 2009, Adam Ratcliffe wrote: > With further experimentation it seems that 32767 does seem to be the correct > value for the -srcnodata option. I've also found that if I omit the > -dstnodata option from the gdalwarp command the black holes do not appear, > presumably because the void data is then not included in the reprojected > image. > On 1/10/2009, at 3:56 PM, Adam Ratcliffe wrote: >> I've created a hillshade image using the NASA SRTM3 data following the >> notes at: http://wiki.openstreetmap.org/wiki/HikingBikingMaps. Looks great >> except for the occasional 'black hole' in the image, I expect this is due >> to data voids not being rendered correctly. >> >> What's got me puzzled about this is that the wiki page suggests using a >> value of 32767 for the -srcnodata and -dstnodata options to gdalwarp, >> howver in the NASA docs >> (http://dds.cr.usgs.gov/srtm/version2_1/Documentation/Quickstart.pdf) it >> says data voids are assigned the value -32768. >> >> Should I be using the NASA value for -srcnodata and -dstnodata instead? Thanks for working this out! Maybe you can correct the wiki page? I wrote that Wiki page, and I just remember that at that time (a year ago) the interpretation was unclear for me. I remember having some problems and experimenting; but in my region, there are no voids, so I might not have found the right solution at that time. And I remember encountering "black holes" later on in other regions (thinking there is no way around having them, without setting them explicitly to some arbitrary value), as well. I will try out your suggestions in a few days myself (and might update the page afterwards, if you have not done so then) ... Thanks, Holger _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users
