How to get a WMS GetFeatureInfo response with MapServer in JSON format?

Question

I use Mapserver with the Leaflet JS library and I want to display some attributes informations of a raster file by clicking on the map.
Therefore I use the GetFeatureInfo WMS request in order to return these informations.
I managed to get the infos with the text/html format but I'd like to get a JSON response back in my browser, e.g :

{
    "value": 14.5, // I must precise I use GetFeatureInfo on a raster and the value result corresponds to the value of the pixel 
}

BELOW ARE THE UPDATES :

So I changed the wms_get_feature_info_formalist in the METADATA bloc of my mapfile :

"wms_getfeatureinfo_formatlist" "application/json"

Then, I edited my template as following to return the value of the pixel :

<!-- MapServer Template -->
{
    "value": [value_0] // [value_0] allow the user to get the value of a pixel
}

I edited the mapfile with the OUTPUT format parameter in order to use the JSON format :

OUTPUTFORMAT
  NAME "json"
  MIMETYPE "application/json"
  DRIVER "TEMPLATE"
  FORMATOPTION "FILE=template.js"
END

And as it is written in the docs, I set :

TEMPLATE "EMPTY"

My GetFeatureInfo request is the one (see "application/json" specified in the INFO_FORMAT parameter)

http://IP/cgi-bin/mapserv?map=/var/www/html/mapfiles/test1.map&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetFeatureInfo&BBOX=465348.6282001531,5431156.607774916,697564.3201305186,5503160.28841955&SRS=EPSG:3857&WIDTH=1519&HEIGHT=471&LAYERS=layer1&STYLES=&FORMAT=image/png&TRANSPARENT=true&QUERY_LAYERS=layer1&INFO_FORMAT=application/json&X=766&Y=261

But when I try the GetFeatureInfo request, my browser returns a JSON response but with the following error message :

SyntaxError: JSON.parse: unexpected character at line 2 column 11 of the JSON data

It seems the [value_0] is not recognized in JSON whereas it works well with the text/html format..
How could I do to make it work ?
I'm really stuck and any help would be greatly appreciated !

Answer 1

There is a working example of a raster layer with a GetFeatureInfo query returning GeoJSON at https://app.mapserverstudio.net/#fXO3XBRn No templates are required, just the OUTPUTFORMAT:

    OUTPUTFORMAT
        NAME "geojson"
        DRIVER "OGR/GEOJSON"
        MIMETYPE "application/json; subtype=geojson; charset=utf-8"
        FORMATOPTION "FORM=SIMPLE"
        FORMATOPTION "STORAGE=memory"
        FORMATOPTION "LCO:NATIVE_MEDIA_TYPE=application/vnd.geo+json"
    END

    WEB
        METADATA
            "wms_enable_request" "*"
            # ensure the outputformat is in this list below
            "wms_getfeatureinfo_formatlist" "geojson"
        END
    END

Counter intuitively the "gml_include_items" is important at the LAYER level even though it is for a raster layer.

    LAYER
        NAME "hillsahde"
        STATUS ON
        TYPE RASTER
        DATA "/data/copernicus/eu_dem_v11_E10N00.TIF"
        PROCESSING "BANDS=1"
        CLASS
            STYLE
                COLORRANGE "#abc270" "#f7f1e5"
                DATARANGE 0 2000
            END
        END
        TEMPLATE "ttt"
        METADATA
            "gml_include_items" "all"
            "gml_types" "auto"
        END
    END

A sample request is:

https://api.mapserverstudio.net/mapserver/?map=/etc/mapserver/mapfiles/output/f920137d-5f1d-4ac4-9bf4-4a86bf4f2b7e.map&SERVICE=WMS&VERSION=1.3.0&REQUEST=GetFeatureInfo&FORMAT=image/png&TRANSPARENT=true&QUERY_LAYERS=hillsahde&LAYERS=hillsahde&STYLES=&FILTER=&INFO_FORMAT=geojson&I=50&J=50&CRS=EPSG:3857&WIDTH=101&HEIGHT=101&BBOX=1799862.1893692566,967876.9675296084,1801451.8980644122,969466.6762247642&_dc=1694810648114

This returns the following GeoJSON:

{
"type": "FeatureCollection",
"name": "hillsahde",
"crs": { "type": "name", "properties": { "name": "urn:ogc:def:crs:EPSG::3857" } },
"features": [
{ "type": "Feature", "properties": { "x": "1800662.5", "y": "968662.5", "value_0": "1349.0573", "value_list": "1349.0573", "class": "0", "red": "-1", "green": "-1", "blue": "-1" }, "geometry": { "type": "Point", "coordinates": [ 1800662.5, 968662.5 ] } }
]
}

You can construct and call this URL with JavaScript with a fetch call (or older style AJAX call) and you can do whatever you want with the GeoJSON in the browser. In the example above the GeoJSON is displayed in a grid when the map is clicked. This functionality is part of a client like OpenLayers - https://openlayers.org/en/latest/examples/getfeatureinfo-tile.html

Answer 2

Meanwhile you wrote your mail I managed to make the JSON output to work to some extent.

In my mapfile I have now at level MAP-WEB-METADATA an entry

 "wms_feature_info_mime_type" "application/json"

I wrote a section for json output

OUTPUTFORMAT
  NAME "json"
  MIMETYPE "application/json"
  DRIVER "TEMPLATE"
  FORMATOPTION "FILE=c:/ms4w_data/myTemplate.js"
END

As a template file I used this

<!-- mapserver template -->
{"foo": "bar"}

In LAYER I have dummy TEMPLATE

TEMPLATE "EMPTY"

The only reason to have the keyword TEMPLATE here is to make the the layer queryable. If the value points to some existing file instead of "EMPTY" the file still won't be read.

Now the GetFeatureInfo request with INFO_FORMAT=application/json returns a response that opens directly on a browser

and it opens to browser because the MIME type is set correctly

What I did not manage to work yet is how to use the raster attributes https://mapserver.org/input/raster.html#raster-query inside the JSON template.

Answer 3

In the past I have used the following, but neither worked for me correctly, things may have changed in recent versions:

# Neither GeoJSON outputs work as expected... (formatoptions issue related to GDAL version?)
# Supported GDAL should support options so MapServer issue?
# Can get GeoJSON by requesting srsname=EPSG:4326 even if bounding box is different
# GeoJSON 2008 (any CRS) BUT missing "crs" property in output)
# See https://www.gdal.org/drv_geojson.html for FORMATOPTIONs
# LCO: ~ is layer creation options prefix
# Pure GeoJSON (CRS:84 only)
# need to use outputformat=application/vnd.geo%2Bjson& in URL request
# or shortcut use name like outputformat=GeoJSON
OUTPUTFORMAT
    NAME "GeoJSON"
    DRIVER "OGR/GEOJSON"
    # MIMETYPE "application/geo+json"
    MIMETYPE "application/vnd.geo+json"
    EXTENSION "geojson"
    FORMATOPTION "LCO:RFC7946=YES"
    FORMATOPTION "STORAGE=stream"
    FORMATOPTION "FORM=SIMPLE"
    FORMATOPTION "LCO:NATIVE_DATA=YES"
    #FORMATOPTION "LCO:NATIVE_MEDIA_TYPE=application/geo+json"
    # Above is correct for GeoJSON, but GDAL requires older deprecated version
    FORMATOPTION "LCO:NATIVE_MEDIA_TYPE=application/vnd.geo+json"
    FORMATOPTION "LCO:COORDINATE_PRECISION=8"
    FORMATOPTION "LCO:WRITE_BBOX=YES"
    FORMATOPTION "FILENAME=result.geojson"
    FORMATOPTION "LCO:DESCRIPTION=This should be GeoJSON (RFC7946); i.e. coordinates in CRS:84 WGS84 datum and decimal degrees in lon lat order, but at the moment it's not working or not supported (https://github.com/mapserver/mapserver/issues/5723)"
END
OUTPUTFORMAT
    NAME "JSON"
    DRIVER "OGR/GEOJSON"
    EXTENSION "json"
    FORMATOPTION "FILENAME=result.json"
    FORMATOPTION "FORM=SIMPLE"
    FORMATOPTION "LCO:COORDINATE_PRECISION=8"
    FORMATOPTION "LCO:DESCRIPTION=This should be GeoJSON 2008; the projection may not be in CRS:84, but if not there should be a crs: member telling you what projection has been used"
    FORMATOPTION "LCO:NATIVE_DATA=YES"
    FORMATOPTION "LCO:WRITE_BBOX=YES"
    FORMATOPTION "STORAGE=stream"
    MIMETYPE "application/json; subtype=geojson"
END

Answer 4

Have you looked at that gml_* entries - you can use them to return attribute data that leaflet should be able to work with e.g.

"gml_include_items" "all"
"gml_featureid" "ID"