I try to generate world coastline 1:30000 from ASTER's DEM with:

gdal_contour -a ELEVATION -fl 0

But above produce some of missing coastlines. Whats happening? Is it cliffy shore? How would you generate coastline?

Note: If I use 0.5 it will show all but I'm afraid it'd be inaccurate. Furthermore how to cleanup "tails" using v.clean?

I found ASTER mirror (mediafire) here: http://sasgis.ru/forum/viewtopic.php?f=21&t=1848&start=360

  • @Devdatta: So is 0.5 okay? I found at minimum 0.02 will still show the coastline except those area plagued by sea of ice. – Malinkundang Sep 26 '13 at 22:45
  • hmm I don't know that. My initial assumption is ASTER is terrestrial radar so what shown is surface (not under water surface). A quick crosscheck with google map satellite reveal it's somewhat accurate at 0.02 but in area such estuaries ASTER is much smaller (lower) – Malinkundang Sep 27 '13 at 1:49
  • I have withdrawn my earlier comments. After a reading of the readme document that comes with ASTER GDEM v 2, I can see that they have applied a sea water body mask, which gives 0 pixel value for the sea area. – Devdatta Tengshe Sep 27 '13 at 4:54
  • 1
    I'll also like to clarify that the vertical datum for ASTER is the EGM96 geoid (jspacesystems.or.jp/ersdac/GDEM/ver2Validation/…) – Devdatta Tengshe Sep 27 '13 at 5:33

At this resolution the ASTER GDEM does not always have cells with a elevation level of 0. They could for instance go from -5 directly to 2, without the intermediate 0 step which is extracted by your gdal_contour command.

Easiest way to do what you want is to reclassify a portion of your DEMs values. For instance you could set all values between -5 and +5 to 0. Then run your gdal_contour command again.

  • sorry, I'm new to DEM. How to reclassify? – Malinkundang Sep 25 '13 at 22:59
  • nevermind I found it – Malinkundang Sep 25 '13 at 23:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.