node-mapnik variables not used in Grids

.gitignore

result.*
node_modules/

README.md

Requirements

We are gonna use a Postgis datasource to check variables propagation. To run the scripts we expect:

• A PostgreSQL database available as postgresql://postgres@localhost:5432/postgres, with PostGIS.

Install

npm install

Test scripts

It's possible to use variables with mapnik.Image, check with:

node test-image.js

However, it's not possible to use them with mapnik.Grid, check with:

node test-grid.js

package.json

{
  "private": true,
  "name": "node-mapnik-grid-variables",
  "version": "1.0.0",
  "description": "",
  "main": "test-grid.js",
  "dependencies": {
    "mapnik": "^3.6.0"
  }
}

postgis-variables.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE Map[]>
<Map srs="+init=epsg:3857" maximum-extent="-20037508.3,-20037508.3,20037508.3,20037508.3">

<Parameters>
  <Parameter name="maximum-extent"><![CDATA[-20037508.3,-20037508.3,20037508.3,20037508.3]]></Parameter>
  <Parameter name="format">png8:m=h</Parameter>
  <Parameter name="interactivity_layer">basic</Parameter>
  <Parameter name="interactivity_fields">id,size</Parameter>
</Parameters>


<Style name="basic" filter-mode="first">
  <Rule>
    <MarkersSymbolizer width="10 * [size]" fill="#ff0000" fill-opacity="0.9" allow-overlap="true" stroke-width="0" stroke="#ffffff" stroke-opacity="1" comp-op="multiply" clip="true" />
  </Rule>
</Style>
<Layer name="basic"
  srs="+init=epsg:3857">
    <StyleName>basic</StyleName>
    <Datasource>
       <Parameter name="type"><![CDATA[postgis]]></Parameter>
       <Parameter name="host"><![CDATA[localhost]]></Parameter>
       <Parameter name="port"><![CDATA[5432]]></Parameter>
       <Parameter name="user"><![CDATA[postgres]]></Parameter>
       <Parameter name="password"></Parameter>
       <Parameter name="dbname"><![CDATA[postgres]]></Parameter>
       <Parameter name="geometry_field"><![CDATA[the_geom_webmercator]]></Parameter>
       <Parameter name="srid"><![CDATA[3857]]></Parameter>
       <Parameter name="table"><![CDATA[(SELECT i AS id, ST_SetSRID(ST_MakePoint(i*1000000,0), 3857) AS the_geom_webmercator, @size AS size FROM generate_series(1,5) as i) as _query]]></Parameter>
       <Parameter name="extent"><![CDATA[-20037508.3,-20037508.3,20037508.3,20037508.3]]></Parameter>
       <Parameter name="simplify_geometries"><![CDATA[false]]></Parameter>
       <Parameter name="row_limit"><![CDATA[0]]></Parameter>
       <Parameter name="persist_connection"><![CDATA[false]]></Parameter>
       <Parameter name="twkb_encoding"><![CDATA[true]]></Parameter>
    </Datasource>
  </Layer>

</Map>

test-grid.js

'use strict';

var mapnik = require('mapnik');
var fs = require('fs');
var assert = require('assert');

mapnik.register_default_fonts();
mapnik.register_default_input_plugins();
var map = new mapnik.Map(256, 256);
var size = 10;

map.load('./postgis-variables.xml', function(err, map) {
    assert.ifError(err);
    map.zoomAll();
    var grid = new mapnik.Grid(256, 256);
    map.render(grid, { layer: 0, fields: ['id', 'size'], variables: { size: size } }, function(err, grid) {
        assert.ifError(err);
        grid.encode({format: 'utf'}, function(err, result) {
            assert.ifError(err);
            var keys = Object.keys(result.data).filter(function(k) { return k !== ''; });
            assert.equal(keys.length, 5);
            keys.forEach(function(k) {
                assert.equal(result.data[k].size, size);
            });
            fs.writeFile('result.grid.json', JSON.stringify(result, null, 4), 'utf-8');
         });
    });
});

test-image.js

'use strict';

var mapnik = require('mapnik');
var fs = require('fs');
var assert = require('assert');

mapnik.register_default_fonts();
mapnik.register_default_input_plugins();
var map = new mapnik.Map(256, 256);
var size = 10;

map.load('./postgis-variables.xml', function(err, map) {
    assert.ifError(err);
    map.zoomAll();
    var image = new mapnik.Image(256, 256);
    map.render(image, {variables: { size: size }}, function(err, im) {
        assert.ifError(err);
        im.encode('png', function(err, buffer) {
            assert.ifError(err);
            fs.writeFile('result.png', buffer);
         });
    });
});