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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  • I have withdrawn my earlier comments.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
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    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
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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

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