Hi all,

I'm being pulled out of retirement to fix something I created years ago. I'm probably doing something stupid but I haven't been able to sort it out, so ask for some help.

System: Ubuntu-22.04
GDAL 3.4.1, released 2021/12/27
OpenLayers 5.3.3
MapServer version 7.6.4 OUTPUT=PNG OUTPUT=JPEG OUTPUT=KML SUPPORTS=PROJ SUPPORTS=AGG SUPPORTS=FREETYPE SUPPORTS=CAIRO SUPPORTS=SVG_SYMBOLS SUPPORTS=RSVG SUPPORTS=ICONV SUPPORTS=FRIBIDI SUPPORTS=WMS_SERVER SUPPORTS=WMS_CLIENT SUPPORTS=WFS_SERVER SUPPORTS=WFS_CLIENT SUPPORTS=WCS_SERVER SUPPORTS=SOS_SERVER SUPPORTS=FASTCGI SUPPORTS=THREADS SUPPORTS=GEOS SUPPORTS=POINT_Z_M SUPPORTS=PBF INPUT=JPEG INPUT=POSTGIS INPUT=OGR INPUT=GDAL INPUT=SHAPEFILE

Right some of this is pretty old, but I suspect that is not the current issue.

1. I extract some data from HYCOM and generate a GTiff
2. Manually generate a VRT to add a color table
3. Have a mapserver mapfile to display it

Step 1. seems to work fine, but when I do a mapserver query I get no results
Step 2. seems to look good and if a gdal_translate -of PNG -outsize 1% 1% source target the image displays
Step 3. just gives me empty transparent tiles in OpenLayers

Here is the gdalinfo results for the GTif:

$ gdalinfo -stats -hist HYCOM_tomorrow_mld.tif
Driver: GTiff/GeoTIFF
Files: HYCOM_tomorrow_mld.tif
Size is 4500, 4251
Coordinate System is:
GEOGCRS["WGS 84",
    DATUM["World Geodetic System 1984",
        ELLIPSOID["WGS 84",6378137,298.257223563,
            LENGTHUNIT["metre",1]]],
    PRIMEM["Greenwich",0,
        ANGLEUNIT["degree",0.0174532925199433]],
    CS[ellipsoidal,2],
        AXIS["geodetic latitude (Lat)",north,
            ORDER[1],
            ANGLEUNIT["degree",0.0174532925199433]],
        AXIS["geodetic longitude (Lon)",east,
            ORDER[2],
            ANGLEUNIT["degree",0.0174532925199433]],
    ID["EPSG",4326]]
Data axis to CRS axis mapping: 2,1
Origin = (-180.000000000000000,90.000000000000000)
Pixel Size = (0.080000000000000,-0.040000000000000)
Metadata:
  AREA_OR_POINT=Area
Image Structure Metadata:
  INTERLEAVE=BAND
Corner Coordinates:
Upper Left  (-180.0000000,  90.0000000) (180d 0' 0.00"W, 90d 0' 0.00"N)
Lower Left  (-180.0000000, -80.0400000) (180d 0' 0.00"W, 80d 2'24.00"S)
Upper Right ( 180.0000000,  90.0000000) (180d 0' 0.00"E, 90d 0' 0.00"N)
Lower Right ( 180.0000000, -80.0400000) (180d 0' 0.00"E, 80d 2'24.00"S)
Center      (   0.0000000,   4.9800000) (  0d 0' 0.01"E, 4d58'48.00"N)
Band 1 Block=4500x1 Type=Float32, ColorInterp=Gray
  Minimum=2.000, Maximum=5000.000, Mean=96.114, StdDev=346.786
0...10...20...30...40...50...60...70...80...90...100 - done.
  256 buckets from -7.8 to 5009.8:
  1489490 2306537 1907189 2028756 996825 306674 493493 0 196427 0 94515 0 0 33174 0 22423 0 0 11571 0 5892 0 0 0 0 8326 0 0 0 0 0 8045 0 0 0 0 7615 0 0 0 0 6418 0 0 0 0 5695 0 0 0 0 4944 0 0 0 0 0 0 0 0 0 0 0 0 13673 0 0 0 0 0 0 0 0 0 0 0 17543 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 31132 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 30109 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 40660 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 28594 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1702
  NoData Value=-30000
  Overviews: 2250x2126, 1125x1063, 563x532, 282x266, 141x133, 71x67
  Metadata:
    STATISTICS_MAXIMUM=5000
    STATISTICS_MEAN=96.114400289494
    STATISTICS_MINIMUM=2
    STATISTICS_STDDEV=346.78571541402
    STATISTICS_VALID_PERCENT=52.78

My assumption based on this is that I want to scale the 5000 to 250 in the VRT which will be Type=Byte, So here is the VRT file.

$ cat HYCOM_tomorrow_mld.vrt                <VRTDataset rasterXSize="72000" rasterYSize="68016">   <SRS>GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433],AUTHORITY["EPSG","4326"]]</SRS>
  <GeoTransform> -180.0 ,0.005 , 0 , 90.0 , 0 , -0.0025 </GeoTransform>
  <Metadata>
  </Metadata>
  <VRTRasterBand dataType="Byte" band="1">
    <ColorInterp>Palette</ColorInterp>
    <ColorTable>
      <Entry c1="0" c2="0" c3="0" c4="255"/>

      [Snip lots of entries]

      <Entry c1="255" c2="255" c3="255" c4="255"/>
    </ColorTable>
    <ComplexSource resampling="bilinear">
      <SourceFilename relativeToVRT="1">HYCOM_tomorrow_mld.tif</SourceFilename>
      <SourceBand>1</SourceBand>
      <SrcRect xOff="0" yOff="0" xSize="4500" ySize="4251"/>
      <DstRect xOff="0" yOff="0" xSize="72000" ySize="68016"/>
      <ScaleRatio>1</ScaleRatio>
      <NODATA>0</NODATA>
    </ComplexSource>
  </VRTRasterBand>
</VRTDataset>

So to scale the data I set ScaleRatio to 0.05, but the PNG image doesn't look right and setting it to "1" does look correct. I'm also confused as to what to set NODATA value to. One source said/implied that the NoData of the source file would get set to NODATA value in the VRT, but seem to be countered by the GDAL online docs.

Here is the gdalinfo for the VRT:

$ gdalinfo -stats -hist HYCOM_tomorrow_mld.vrt
Driver: VRT/Virtual Raster
Files: HYCOM_tomorrow_mld.vrt
       HYCOM_tomorrow_mld.tif
Size is 72000, 68016
Coordinate System is:
GEOGCRS["WGS 84",
    DATUM["World Geodetic System 1984",
        ELLIPSOID["WGS 84",6378137,298.257223563,
            LENGTHUNIT["metre",1]]],
    PRIMEM["Greenwich",0,
        ANGLEUNIT["degree",0.0174532925199433]],
    CS[ellipsoidal,2],
        AXIS["geodetic latitude (Lat)",north,
            ORDER[1],
            ANGLEUNIT["degree",0.0174532925199433]],
        AXIS["geodetic longitude (Lon)",east,
            ORDER[2],
            ANGLEUNIT["degree",0.0174532925199433]],
    ID["EPSG",4326]]
Data axis to CRS axis mapping: 2,1
Origin = (-180.000000000000000,90.000000000000000)
Pixel Size = (0.005000000000000,-0.002500000000000)
Corner Coordinates:
Upper Left  (-180.0000000,  90.0000000) (180d 0' 0.00"W, 90d 0' 0.00"N)
Lower Left  (-180.0000000, -80.0400000) (180d 0' 0.00"W, 80d 2'24.00"S)
Upper Right ( 180.0000000,  90.0000000) (180d 0' 0.00"E, 90d 0' 0.00"N)
Lower Right ( 180.0000000, -80.0400000) (180d 0' 0.00"E, 80d 2'24.00"S)
Center      (   0.0000000,   4.9800000) (  0d 0' 0.01"E, 4d58'48.00"N)
Band 1 Block=128x128 Type=Byte, ColorInterp=Palette
  Minimum=2.000, Maximum=5000.000, Mean=96.114, StdDev=346.786
0...10...20...30...40...50...60...70...80...90...100 - done.
  256 buckets from -0.5 to 255.5:
  0 0 534720 0 330663 0 149196 0 241797 0 233114 0 285113 0 0 385666 0 0 0 0 574491 0 0 0 0 517919 0 0 0 0 543348 0 0 0 0 455442 0 0 0 0 487763 0 0 0 0 530058 0 0 0 0 433926 0 0 0 0 0 0 0 0 0 1117668 0 0 0 0 0 0 0 0 0 911088 0 0 0 0 0 0 0 0 0 602087 0 0 0 0 0 0 0 0 0 394738 0 0 0 0 0 0 0 0 0 306674 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 493493 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 196427 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 94515 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 33174 0 0 0 0 244342   Overviews: 36000x34016, 18000x17008, 9008x8512, 4512x4256, 2256x2128, 1136x1072
  Metadata:
    STATISTICS_MAXIMUM=5000
    STATISTICS_MEAN=96.114400289494
    STATISTICS_MINIMUM=2
    STATISTICS_STDDEV=346.78571541402
  Color Table (RGB with 256 entries)
    0: 0,0,0,255
    [snip additional entries]

And finally the mapfile that is getting used via OpenLayers:

MAP
    NAME "HYCOM_2d_2"
    STATUS ON
    SIZE 950 600
    EXTENT -180 -90 180 90
    UNITS DD
    IMAGECOLOR "#000000"
    IMAGETYPE agg_qn
    MAXSIZE 4096

    CONFIG ON_MISSING_DATA "IGNORE"
#    CONFIG MS_ERRORFILE "stderr"
#    DEBUG 10

    OUTPUTFORMAT
        NAME "agg_qn"
        DRIVER "AGG/PNG"
        EXTENSION "png"
        MIMETYPE "image/png"
        IMAGEMODE RGBA
        FORMATOPTION "INTERLACE=false"
        FORMATOPTION "QUANTIZE_NEW=ON"
        FORMATOPTION "QUANTIZE_FORCE=ON"
        FORMATOPTION "QUANTIZE_DITHER=OFF"
        FORMATOPTION "QUANTIZE_COLORS=256"
        TRANSPARENT ON
        FORMATOPTION "TRANSPARENT=ON"
    END

    OUTPUTFORMAT
        NAME aggpng24
        DRIVER AGG/PNG
        MIMETYPE "image/png"
        IMAGEMODE RGB
        EXTENSION "png"
    END

    OUTPUTFORMAT
        NAME jpeg
        DRIVER AGG/JPEG
        MIMETYPE "image/jpeg"
        IMAGEMODE RGB
        EXTENSION "jpg"
        FORMATOPTION "GAMMA=0.75"
        FORMATOPTION "QUALITY=75"
    END

    WEB
        METADATA
            labelcache_map_edge_buffer "-20"
            "ows_title"     "iMaptools - HYCOM data"
            "ows_onlineresource" "http://map01.saltwatercentral.com/cgi-bin/mapserv?MAP=/maps/wms/hycom_2d_2.map";
            "ows_srs"       "EPSG:4326 EPSG:900913 EPSG:3857"
            "ows_contactperson"     "Stephen Woodbridge"
            "ows_contactorganization" "iMaptools.com"
            "ows_contactposition"   "Owner"
            "ows_contactelectronicmailaddress" "i...@imaptools.com"
            "ows_enable_request" "GetMap"
            "ows_http_max_age" "3200"
        END
    END

    PROJECTION "init=epsg:4326" END

    LAYER
        NAME "ssh"
        STATUS ON
        TYPE RASTER
        PROJECTION "init=epsg:4326" END
        DATA "/maps/wms/data/HYCOM/HYCOM_tomorrow_ssh.vrt"
        PROCESSING "NODATA=-30000"
        PROCESSING "SCALE=-1.0,1.0"
    END

    LAYER
        NAME "mlt"
        STATUS ON
        TYPE RASTER
        PROJECTION "init=epsg:4326" END
        DATA "/maps/wms/data/HYCOM/HYCOM_tomorrow_mlt.vrt"
        #PROCESSING "NODATA=1.2676506002282294e+30"
        PROCESSING "NODATA=-30000"
        PROCESSING "SCALE=0,250"
    END

    LAYER
        NAME "query"
        STATUS ON
        TYPE raster
        PROJECTION "init=epsg:4326" END
        VALIDATION 'type' '.' END
        TOLERANCE 0
        TOLERANCEUNITS pixels
        DATA "/maps/wms/data/HYCOM/HYCOM_tomorrow_%type%.tif"
        PROCESSING "NODATA=-30000"
        TEMPLATE "/maps/wms/pixel.value.html"
    END

END

I've tried various options of including PROCESSING "NODATA=' and PROCESSING "SCALE=" to no success. And the "ssh" layer which is nearly identical seems to would fine.

It get displayed via OpenLayers using a layer definition like:

    hycom_mlt_2: new TileLayer({
        title: 'Mixed Layer Depth (0.3degC chg)',
        clickable: 'hycom_mlt_2',
        type: 'overlay',
        visible: false,
        source: new TileWMS({
            projection: 'EPSG:3857',
            urls: getMapUrls('//', map_hosts, '/cgi-bin/mapserv?map=/maps/wms/hycom_2d_2.map'),
            params: {
                'LAYERS': 'mlt',
                'format': 'image/png',
                'version': '1.3.0'
            }
        })
    }),


I would appreciate any assistance in figuring out what I'm doing wrong.

Thanks,
  Steve

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