[mapserver-users] Point query from Mapserver raster

[Rahkonen Jukka (MML)]

Hi,

The WMS GetFeatureInfo should work and the answer in gis.stackexhange seems to contain all the details that you need for making it to work.
With WCS what you did is probably the best you can do with Mapserver. With some other servers you may get a single pixel output by using WCS slicing (subset=Long(-100)&subset=Lat(22)) or trimming with lowerlimit=upperlimit (subset=Long(-100,-100)&subset=Lat(22,22)) but Mapserver does not support either. See https://osgeo-org.atlassian.net/browse/GEOS-9553.

I could not find a link to an answer by Stefan Meissl about why Mapserver does not support slicing but it was about dimensions. A raster image can be considered to be two dimensional even when it has only one pixel, but by the WCS standard each trim is removing one dimension. Slicing DEM with two axes must return a zero dimensional result and raster formats do not support that. I still think that subsets with lower=upper limits should works and return a single pixel output but that does not work with either Mapserver or Geoserver. See also https://www.mail-archive.com/search?l=mapserver-users%40lists.osgeo.org&q=subject:%22%5C%5Bmapserver%5C-users%5C%5D+WCS+GetCoverage+request+one++by+one+pixel%22&o=newest&f=1


-Jukka Rahkonen-


Lähettäjä: MapServer-users <mapserver-users-bounces at lists.osgeo.org> Puolesta Carl Godkin
Lähetetty: lauantai 30. lokakuuta 2021 2.10
Vastaanottaja: mapserver-users at lists.osgeo.org
Aihe: [mapserver-users] Point query from Mapserver raster

Hi,
Now that I have my WMS and WCS servers working well (thanks, list!!), I have one more thing I would like to figure out how to do.

I want to do point queries on [Lat,Lon] points for their elevation from the terrain layer I have.

I have done some searching and come across various ideas such as Raster Query (https://mapserver.org/input/raster.html#raster-query) and a query template  (https://gis.stackexchange.com/questions/167239/mapserver-raster-picking-elevation-data) but haven't found enough information for either to implement it.

I came up with a solution that works fine, but might be considered as going "All Around the Barn"   What works is to add an ASCII output format to my map file that serves terrain like this:

    OUTPUTFORMAT
      NAME XYZ
      DRIVER "GDAL/XYZ"
      MIMETYPE "text/plain"
      IMAGEMODE FLOAT32
      EXTENSION "txt"
    END

and then use GetCoverage on a small rectangle whose lower-left corner
is the point whose elevation I want:

http://localhost:8080/wcs?SERVICE=WCS&VERSION=2.0.1&REQUEST=GetCoverage&coverageid=SRTM_3_arc-second_grid&format=XYZ&subset=Lat(42.948,42.958)&subset=Lon(-122.086,-122.076)

and then take the first line of the returned output file.

What would Mapserver best practice be for a problem like this?

Thanks very much,

carl








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