[mapserver-users] Point query from Mapserver raster

Tue Nov 2 09:04:01 PDT 2021

Thanks for the quick response, Jukka.

I did not realize that X/Y had been replaced by I/J.  I just tried that
instead and it still worked (of course) but I still get the warning message.

I had also been trying WMS 1.1.0 and 1.1.1 earlier and I am unable to find
any combination of versions and other query parameters to quiet the warning
message.

Regarding the BBOX range, I opened the range to a full degree in each
direction and still get the warning.  I think I will stick with the query I
posted originally (with 1.3.0) since it works and just ignore the messages
in the log.

This seems like sort of a hack to me (asking for a box when I want a point,
etc.) which is why I asked my question in the first place.  But it works
fine so I'm happy!

Thanks again,

carl

On Tue, Nov 2, 2021 at 8:29 AM Rahkonen Jukka (MML) <
jukka.rahkonen at maanmittauslaitos.fi> wrote:

> Hi,
>
>
>
> You do not seem to do anything wrong. Your WMS 1.3.0 EPSG:4326 lat-long
> BBOX=42.94,-122.09,42.95,-122.08& gets converted into long-lat order and
> for some reason the lower and higher values are equal
> {-122.082500,42.942500,-122.082500,42.942500}, thus this is no more a box
> but a point.
>
> GetFeatureInfo with a small bbox and width=2 and height=2 is a trick that
> is certainly not heavily tested because the corresponding GetMap is pretty
> odd despite being valid.  Maybe using slightly bigger BBOX makes Mapserver
> to query the backend raster with a rectangle instead of a point.
>
> BTW X=1 and Y=1 are not valid in WMS 1.3.0, you are supposed to use i= and
> j= instead. That makes me think that maybe you could have a try with a full
> and valid WMS 1.1.0 GetFeatureInfo request with SRS= and BBOX in long-lat
> order and see if it has any effect on the msProjectRect()
>
>
>
> -Jukka Rahkonen-
>
>
>
> *Lähettäjä:* MapServer-users <mapserver-users-bounces at lists.osgeo.org> *Puolesta
> *Carl Godkin
> *Lähetetty:* tiistai 2. marraskuuta 2021 17.06
> *Vastaanottaja:* mapserver-users at lists.osgeo.org
> *Aihe:* Re: [mapserver-users] Point query from Mapserver raster
>
>
>
> Hi,
>
>
>
> Following Jukka's advice on my elevation point query, I am trying to use
> WMS GetFeatureInfo,
>
>
>
> I've mostly got it working but have a few more questions.  (I am using
> MS4W 4.0.5 which includes MapServer 7.7.0)
>
>
>
> I added a LAYER to my WMS map file:
>
>
>
>   LAYER
>
>     PROCESSING "RESAMPLE=BILINEAR"
>
>     NAME SRTM_3_arc-second_grid
>
>     METADATA
>
>       "wms_title"           "SRTM - 3 arc-second grid"
>
>       "ows_extent"          "-125 24 -66 50"
>
>       "wms_include_items"   "all"
>
>     END
>
>
>
>     TYPE RASTER
>
>     STATUS ON
>
>     TILEINDEX "srtm_3_hgt-index.shp"
>
>     TILEITEM "Location"
>
>     TEMPLATE "../template.html"
>
>     PROJECTION
>
>       "init=epsg:4326"
>
>     END
>
>   END
>
>
>
> and an empty template except for the
>
>
>
> <!-- MapServer Template -->
>
>
>
> line.  Here's my query:
>
>
>
> http://localhost:8080/wms?
>
>   SERVICE=WMS&
>
>   VERSION=1.3.0&
>
>   REQUEST=GetFeatureInfo&
>
>   LAYERS=SRTM_3_arc-second_grid&
>
>   CRS=EPSG:4326&
>
>   BBOX=42.94,-122.09,42.95,-122.08&
>
>   WIDTH=2&
>
>   HEIGHT=2&
>
>   X=1&
>
>   Y=1&
>
>   QUERY_LAYERS=SRTM_3_arc-second_grid
>
>
>
> This works fine and returns the elevation I am expecting.  However, the
> MapServer log complains about a "degenerate rect" every time:
>
>
>
> [Tue Nov  2 07:58:44 2021].66000 msProjectRect(): Warning: degenerate rect
> {-122.082500,42.942500,-122.082500,42.942500}
>
>
>
> What am I doing wrong here?   As I posted originally, I am really only
> interested in a point here.
>
>
>
> Thank you very much,
>
>
>
> carl
>
>
>
>
>
> On Mon, Nov 1, 2021 at 12:58 AM Rahkonen Jukka (MML) <
> jukka.rahkonen at maanmittauslaitos.fi> wrote:
>
> 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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