[gdal-dev] Can I interpret GIBS ASTER_GDEM_Color_Index as elevation somehow?

[Carl Godkin]

Hi again,

I'm interested in trying to use the "Script-level Access via GDAL" guidance
on the NASA "GIBS API for Developers" page:

https://wiki.earthdata.nasa.gov/display/GIBS/GIBS+API+for+Developers

The layer I'm interested in is "ASTER_GDEM_Color_Index" which is elevation
data.

The site contains advice on how to customize a WMS service description file
for the multitude of data types offered and I came up with this:

<GDAL_WMS>
  <Service name="TMS">
    <ServerUrl>
http://map1.vis.earthdata.nasa.gov/wmts-geo/ASTER_GDEM_Color_Index/default/2014-01-01/EPSG4326_31m/${z}/${y}/${x}.png
</ServerUrl>
  </Service>
  <DataWindow>
    <UpperLeftX>-180.0</UpperLeftX>
    <UpperLeftY>90</UpperLeftY>
    <LowerRightX>396.0</LowerRightX>
    <LowerRightY>-198</LowerRightY>
    <TileLevel>11</TileLevel>
    <TileCountX>2</TileCountX>
    <TileCountY>1</TileCountY>
    <YOrigin>top</YOrigin>
  </DataWindow>
  <Projection>EPSG:4326</Projection>
  <BlockSizeX>512</BlockSizeX>
  <BlockSizeY>512</BlockSizeY>
  <BandsCount>4</BandsCount>
</GDAL_WMS>

I made two changes in order to make it work properly.

1. I think that the resolution is actually 31m which I found here

http://map1.vis.earthdata.nasa.gov/wmts-geo/1.0.0/WMTSCapabilities.xml

2. The TileLevel is 11, which I believes follows from the increased
resolution.

Anyway, the following command (adapted from one of the examples on the
page) works beautifully:

gdal_translate -outsize 1200 1000 -projwin -105 42 -93 32 my.xml out.tif

However, it produces four bands of a colored GeoTIFF, whereas I'd like
elevation values instead.

Is there some way to get elevation VALUES from this?

Normally, elevation values in the GDAL world come in a single band.  Did I
overlook another Layer name that has elevation values?  Or is there some
way to lookup elevations given the RGBA values?

Thank you very much,

carl
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/gdal-dev/attachments/20150713/68c1e0a9/attachment.html>