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Guest cbuchner1

NASA SRTM v2 water body coverage - gaping holes?

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Hey there,I was just wondering why there are gaping coverage holes in the NASA SRTM V2 water body database (SWBD). For example in Kenya, Africa an entire chunk of land seems to be missing in the coverage (e.g. e038s02s.zip ... e038s03s.zip)...I wouldn't have noticed, if Tileproxy hadn't turned the entire area into sea... So now I will have to account for missing SWBD tiles and default them to either land or sea, depending on position.So I will need some kind of map that tells me (at 1 degree of arc resolution) where there is supposed to be land and water on absence of NASA data. That's 360 x 180 = 64800 grid elements. I am NOT looking forward to typing this into a two-dimensional char[] array... ;-) Maybe I'll just re-scale a world map to 360x180 pixels and be done with that.Christian

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Hello Christian,How large is the piece of land? Or rather, the area of water, since those are water body data?As per Mil specs, terrain features that are smaller than specs are not represented. It seems the U.S. Army just does not care about them - probably they have the means to ford small (for them) bodies of water without giving it a second thought.Check the documentation for the data.Best regards.Luis

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Hello Christian,the GTOPO30 data keeps ocean areas undefined so it would be pretty straightforward to create a suitable binary (land/water) raster image. On the other had, it's a much higher resolution than you need and there might be other global data sets at 1-degree resolution available already.Anyway, here they are: http://www1.gsi.go.jp/geowww/globalmap-gsi...30/gtopo30.htmlCheers, Holger

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Oh well, I mapped the NASA data onto the Google Earth using a custom kml file. That allowed me to see where the "holes" were and which of these holes actually depicted dry land.All of these holes were actually on land without any significant surface water. Like... the Sahara, some of the desert areas in the US and a lot of places in Arabia, etc...I let a C program output a 360x180 pixel PGM image of the existing SWBD coverage. Then I took a paint program and flood filled the "hole" areas that were not caused by small seas (e.g. the mediterranean, gulf of persia, etc...) or lakes (like e.g. the Great Lakes in the US).So now I have land/water coverage for everything south of 60 degrees North. Why the NASA data is cut off at 60 deg. N, I will never understand. The southern latitudes seem much better covered.

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Ah, didn't know the 54 South limit either."Never say never".I'll fix Tileproxy to know about the southern limit as well.

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