Re: [mkgmap-dev] "Small" SRTM1 files and DEM maps
I also searched for info about this format before posting to the list, but could not find anything either:-( El 17/4/20 a las 6:19, Gerd Petermann escribió:
Hi all,
I could not find any information about this special format. Would be great if someone could point me to a detailed documentation.
Gerd
________________________________________ Von: Gerd Petermann <gpetermann_muenchen@hotmail.com> Gesendet: Donnerstag, 16. April 2020 18:06 An: Carlos Dávila Betreff: AW: [mkgmap-dev] "Small" SRTM1 files and DEM maps
Hi Carlos,
the hgt files are very simple. They contain an array of n * n 16-bit values, nothing else. The 16-bit value gives the elevation, and the file name gives the position of the southwest corner, see https://stackoverflow.com/questions/357415/how-to-read-nasa-hgt-binary-files Maybe the 12.4 MB files use 8-bit values for the elevation, but 12.970.802 / 3601 gives 3602, so there is probably an extra byte giving a delta value. Coud not find a desription of this format so far. I'll try to find out more.
Gerd
________________________________________ Von: Carlos Dávila <carlos@alternativaslibres.org> Gesendet: Donnerstag, 16. April 2020 17:39 An: Gerd Petermann Betreff: Re: [mkgmap-dev] "Small" SRTM1 files and DEM maps
HI Gerd I don't think conversion is wrong. If input geotiff file is 24MB, output hgt file is 24 MB, if input tiff is 12MB, output hgt is 12MB I use this command on Linux: for i in *.tif ; do gdal_translate -strict -q -eco -of SRTMHGT $i `basename $i tif`hgt ; done ; rm -f *.hgt.aux.xml BTW, gdal is also able to deal with small SRTM files
El 16/4/20 a las 11:31, Gerd Petermann escribió:
Hi Carlos,
so your conversion routine is wrong. The file size is 12.970.802 bytes. There is no integer n for which 2 * n^2 results in this value.
Gerd
________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Carlos Dávila <cdavilam@orangecorreo.es> Gesendet: Donnerstag, 16. April 2020 11:19 An: mkgmap-dev@lists.mkgmap.org.uk Betreff: Re: [mkgmap-dev] "Small" SRTM1 files and DEM maps
Hi Gerd Forgot to mention files are downloaded as geotiff, but I then convert them to hgt, sorry. You can download a sample one from https://alternativaslibres.org/tmp/N50E118.hgt
El 16/4/20 a las 9:18, Gerd Petermann escribió:
Hi Carlos,
are you talking about geotiff format? I think someone documented how that format can be converted to *.hgt. Can you post a link to such a file?
Gerd
________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Carlos Dávila <cdavilam@orangecorreo.es> Gesendet: Montag, 13. April 2020 14:08 An: mkgmap-dev@lists.mkgmap.org.uk Betreff: Re: [mkgmap-dev] "Small" SRTM1 files and DEM maps
Hi Gerd They are downloaded by phyghtmap. This is what I found digging into phyghtmap files: |def getSRTMFileServer(self, resolution, srtmVersion):|| || if srtmVersion == 2.1:|| || return "https://dds.cr.usgs.gov/srtm/version2_1/SRTM{0:d}".format(resolution)|| || elif srtmVersion == 3.0:|| || if resolution == 1:|| || urlRe = "https://earthexplorer.usgs.gov/download/8360/SRTM1{:s}V3/GEOTIFF/EE"|| || elif resolution == 3:|| || urlRe = "https://earthexplorer.usgs.gov/download/4960/SRTM3{:s}V2/GEOTIFF3/EE"|| || return urlRe| They should come from the second URL above.
El 13/4/20 a las 8:24, Gerd Petermann escribió:
Hi Carlos,
sorry for the late response. I found no hint on the phyghtmap page http://katze.tfiu.de/projects/phyghtmap/ regarding a new format for srtm data. The hgt format is not compressed. Do you know from where these 12.4 MB files came from?
Gerd
________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Carlos Dávila <cdavilam@orangecorreo.es> Gesendet: Samstag, 11. April 2020 17:09 An: Development list for mkgmap Betreff: [mkgmap-dev] "Small" SRTM1 files and DEM maps
I use phyghtmap to build contour lines and also to download hgt data that I then use to build DEM maps with mkgmap. For a long time, SRTM1 files (and also VFP1) have all been ~24.7 MB in size, but lately (I don't remember since when) SRTM1 are also served as 12.4 MB files. phyghtmap is able to generate contour lines from those small files, as they seem to contain the same information but with a different compression ratio, but mkgmap fails to read them, and report them as missing. Would it be possible to get support for such files in mkgmap? _______________________________________________ mkgmap-dev mailing list mkgmap-dev@lists.mkgmap.org.uk http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev _______________________________________________
mkgmap-dev mailing list mkgmap-dev@lists.mkgmap.org.uk http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev _______________________________________________ mkgmap-dev mailing list mkgmap-dev@lists.mkgmap.org.uk http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
Hi Carlos, maybe you can ask the developers of gdal_translate? Gerd ________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Carlos Dávila <carlos@alternativaslibres.org> Gesendet: Freitag, 17. April 2020 10:32 An: Development list for mkgmap Betreff: Re: [mkgmap-dev] "Small" SRTM1 files and DEM maps I also searched for info about this format before posting to the list, but could not find anything either:-( El 17/4/20 a las 6:19, Gerd Petermann escribió:
Hi all,
I could not find any information about this special format. Would be great if someone could point me to a detailed documentation.
Gerd
________________________________________ Von: Gerd Petermann <gpetermann_muenchen@hotmail.com> Gesendet: Donnerstag, 16. April 2020 18:06 An: Carlos Dávila Betreff: AW: [mkgmap-dev] "Small" SRTM1 files and DEM maps
Hi Carlos,
the hgt files are very simple. They contain an array of n * n 16-bit values, nothing else. The 16-bit value gives the elevation, and the file name gives the position of the southwest corner, see https://stackoverflow.com/questions/357415/how-to-read-nasa-hgt-binary-files Maybe the 12.4 MB files use 8-bit values for the elevation, but 12.970.802 / 3601 gives 3602, so there is probably an extra byte giving a delta value. Coud not find a desription of this format so far. I'll try to find out more.
Gerd
________________________________________ Von: Carlos Dávila <carlos@alternativaslibres.org> Gesendet: Donnerstag, 16. April 2020 17:39 An: Gerd Petermann Betreff: Re: [mkgmap-dev] "Small" SRTM1 files and DEM maps
HI Gerd I don't think conversion is wrong. If input geotiff file is 24MB, output hgt file is 24 MB, if input tiff is 12MB, output hgt is 12MB I use this command on Linux: for i in *.tif ; do gdal_translate -strict -q -eco -of SRTMHGT $i `basename $i tif`hgt ; done ; rm -f *.hgt.aux.xml BTW, gdal is also able to deal with small SRTM files
El 16/4/20 a las 11:31, Gerd Petermann escribió:
Hi Carlos,
so your conversion routine is wrong. The file size is 12.970.802 bytes. There is no integer n for which 2 * n^2 results in this value.
Gerd
________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Carlos Dávila <cdavilam@orangecorreo.es> Gesendet: Donnerstag, 16. April 2020 11:19 An: mkgmap-dev@lists.mkgmap.org.uk Betreff: Re: [mkgmap-dev] "Small" SRTM1 files and DEM maps
Hi Gerd Forgot to mention files are downloaded as geotiff, but I then convert them to hgt, sorry. You can download a sample one from https://alternativaslibres.org/tmp/N50E118.hgt
El 16/4/20 a las 9:18, Gerd Petermann escribió:
Hi Carlos,
are you talking about geotiff format? I think someone documented how that format can be converted to *.hgt. Can you post a link to such a file?
Gerd
________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Carlos Dávila <cdavilam@orangecorreo.es> Gesendet: Montag, 13. April 2020 14:08 An: mkgmap-dev@lists.mkgmap.org.uk Betreff: Re: [mkgmap-dev] "Small" SRTM1 files and DEM maps
Hi Gerd They are downloaded by phyghtmap. This is what I found digging into phyghtmap files: |def getSRTMFileServer(self, resolution, srtmVersion):|| || if srtmVersion == 2.1:|| || return "https://dds.cr.usgs.gov/srtm/version2_1/SRTM{0:d}".format(resolution)|| || elif srtmVersion == 3.0:|| || if resolution == 1:|| || urlRe = "https://earthexplorer.usgs.gov/download/8360/SRTM1{:s}V3/GEOTIFF/EE"|| || elif resolution == 3:|| || urlRe = "https://earthexplorer.usgs.gov/download/4960/SRTM3{:s}V2/GEOTIFF3/EE"|| || return urlRe| They should come from the second URL above.
El 13/4/20 a las 8:24, Gerd Petermann escribió:
Hi Carlos,
sorry for the late response. I found no hint on the phyghtmap page http://katze.tfiu.de/projects/phyghtmap/ regarding a new format for srtm data. The hgt format is not compressed. Do you know from where these 12.4 MB files came from?
Gerd
________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Carlos Dávila <cdavilam@orangecorreo.es> Gesendet: Samstag, 11. April 2020 17:09 An: Development list for mkgmap Betreff: [mkgmap-dev] "Small" SRTM1 files and DEM maps
I use phyghtmap to build contour lines and also to download hgt data that I then use to build DEM maps with mkgmap. For a long time, SRTM1 files (and also VFP1) have all been ~24.7 MB in size, but lately (I don't remember since when) SRTM1 are also served as 12.4 MB files. phyghtmap is able to generate contour lines from those small files, as they seem to contain the same information but with a different compression ratio, but mkgmap fails to read them, and report them as missing. Would it be possible to get support for such files in mkgmap? _______________________________________________ mkgmap-dev mailing list mkgmap-dev@lists.mkgmap.org.uk http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev _______________________________________________
mkgmap-dev mailing list mkgmap-dev@lists.mkgmap.org.uk http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev _______________________________________________ mkgmap-dev mailing list mkgmap-dev@lists.mkgmap.org.uk http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
_______________________________________________ mkgmap-dev mailing list mkgmap-dev@lists.mkgmap.org.uk http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
This is what I have received by now: The file with half size have probably width=1801 at higher latitudes (60deg I believe) GDAL SRTMHGT driver source code at https://github.com/OSGeo/gdal/blob/master/gdal/frmts/srtmhgt/srtmhgtdataset.... I'm also awaiting for a reply from Earthexplorer... El 17/4/20 a las 10:43, Gerd Petermann escribió:
Hi Carlos,
maybe you can ask the developers of gdal_translate?
Gerd
________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Carlos Dávila <carlos@alternativaslibres.org> Gesendet: Freitag, 17. April 2020 10:32 An: Development list for mkgmap Betreff: Re: [mkgmap-dev] "Small" SRTM1 files and DEM maps
I also searched for info about this format before posting to the list, but could not find anything either:-(
El 17/4/20 a las 6:19, Gerd Petermann escribió:
Hi all,
I could not find any information about this special format. Would be great if someone could point me to a detailed documentation.
Gerd
________________________________________ Von: Gerd Petermann <gpetermann_muenchen@hotmail.com> Gesendet: Donnerstag, 16. April 2020 18:06 An: Carlos Dávila Betreff: AW: [mkgmap-dev] "Small" SRTM1 files and DEM maps
Hi Carlos,
the hgt files are very simple. They contain an array of n * n 16-bit values, nothing else. The 16-bit value gives the elevation, and the file name gives the position of the southwest corner, see https://stackoverflow.com/questions/357415/how-to-read-nasa-hgt-binary-files Maybe the 12.4 MB files use 8-bit values for the elevation, but 12.970.802 / 3601 gives 3602, so there is probably an extra byte giving a delta value. Coud not find a desription of this format so far. I'll try to find out more.
Gerd
________________________________________ Von: Carlos Dávila <carlos@alternativaslibres.org> Gesendet: Donnerstag, 16. April 2020 17:39 An: Gerd Petermann Betreff: Re: [mkgmap-dev] "Small" SRTM1 files and DEM maps
HI Gerd I don't think conversion is wrong. If input geotiff file is 24MB, output hgt file is 24 MB, if input tiff is 12MB, output hgt is 12MB I use this command on Linux: for i in *.tif ; do gdal_translate -strict -q -eco -of SRTMHGT $i `basename $i tif`hgt ; done ; rm -f *.hgt.aux.xml BTW, gdal is also able to deal with small SRTM files
El 16/4/20 a las 11:31, Gerd Petermann escribió:
Hi Carlos,
so your conversion routine is wrong. The file size is 12.970.802 bytes. There is no integer n for which 2 * n^2 results in this value.
Gerd
________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Carlos Dávila <cdavilam@orangecorreo.es> Gesendet: Donnerstag, 16. April 2020 11:19 An: mkgmap-dev@lists.mkgmap.org.uk Betreff: Re: [mkgmap-dev] "Small" SRTM1 files and DEM maps
Hi Gerd Forgot to mention files are downloaded as geotiff, but I then convert them to hgt, sorry. You can download a sample one from https://alternativaslibres.org/tmp/N50E118.hgt
El 16/4/20 a las 9:18, Gerd Petermann escribió:
Hi Carlos,
are you talking about geotiff format? I think someone documented how that format can be converted to *.hgt. Can you post a link to such a file?
Gerd
________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Carlos Dávila <cdavilam@orangecorreo.es> Gesendet: Montag, 13. April 2020 14:08 An: mkgmap-dev@lists.mkgmap.org.uk Betreff: Re: [mkgmap-dev] "Small" SRTM1 files and DEM maps
Hi Gerd They are downloaded by phyghtmap. This is what I found digging into phyghtmap files: |def getSRTMFileServer(self, resolution, srtmVersion):|| || if srtmVersion == 2.1:|| || return "https://dds.cr.usgs.gov/srtm/version2_1/SRTM{0:d}".format(resolution)|| || elif srtmVersion == 3.0:|| || if resolution == 1:|| || urlRe = "https://earthexplorer.usgs.gov/download/8360/SRTM1{:s}V3/GEOTIFF/EE"|| || elif resolution == 3:|| || urlRe = "https://earthexplorer.usgs.gov/download/4960/SRTM3{:s}V2/GEOTIFF3/EE"|| || return urlRe| They should come from the second URL above.
El 13/4/20 a las 8:24, Gerd Petermann escribió:
Hi Carlos,
sorry for the late response. I found no hint on the phyghtmap page http://katze.tfiu.de/projects/phyghtmap/ regarding a new format for srtm data. The hgt format is not compressed. Do you know from where these 12.4 MB files came from?
Gerd
________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Carlos Dávila <cdavilam@orangecorreo.es> Gesendet: Samstag, 11. April 2020 17:09 An: Development list for mkgmap Betreff: [mkgmap-dev] "Small" SRTM1 files and DEM maps
I use phyghtmap to build contour lines and also to download hgt data that I then use to build DEM maps with mkgmap. For a long time, SRTM1 files (and also VFP1) have all been ~24.7 MB in size, but lately (I don't remember since when) SRTM1 are also served as 12.4 MB files. phyghtmap is able to generate contour lines from those small files, as they seem to contain the same information but with a different compression ratio, but mkgmap fails to read them, and report them as missing. Would it be possible to get support for such files in mkgmap? _______________________________________________ mkgmap-dev mailing list mkgmap-dev@lists.mkgmap.org.uk http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev _______________________________________________
participants (2)
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Carlos Dávila -
Gerd Petermann