How to symbolize text with mapnik3

[giantchen2012]

Guys, I'm using mapnik3 in python3, and unfortunately found that TextSymbolizer and ShieldSymbolizer has no support in python3, so any alternative solution?

How to show the name of these points??

[talaj]

Unfortunately these symbolizers are not well covered by current Python bindings, but you can style them in the XML style.

[giantchen2012]

Alright, but how can i programmatically use apply style in xml to each point? BTW any plan for this issue?

[talaj]

Can you be more precise, please? I cannot imagine what exactly you want to do.

BTW any plan for this issue?

I have plans, but no time or energy.

[giantchen2012]

@talaj ,great appreciate for your quick reply. In my case, all the points was generated in my program dynamically.More specifically, I want to find points in ten miles around the point where my mouse clicked and show them off with specified icon and text.

[talaj]

I think there is more ways how to do that. If you are using Postgis, you can simply mark geometries around some point by query such as this:

select geometry, ST_Distance(geometry, 'SRID=my_srid;POINT(my_x my_y)'::geometry) < my_distance as highlight from my_geom_table

You can prepare an XML file with following style definition:

<Style name="my_points">
    <Rule>
        <Filter>[highlight]</Filter>
            ... highlighted style ...
    </Rule>
    <Rule>
        <ElseFilter />
            ... normal style ...
    </Rule>
</Style>

Then load the XML and create Layer programatically like in the following test: https://github.com/mapnik/python-mapnik/blob/8481096ebaa94e907a505c1dc6bebec4294ab19f/test/python_tests/postgis_test.py#L1022-L1026

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Simplest way from point of Mapnik is to emit XML style with required properties programmatically, and then just load it with Mapnik.

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Another way how to achieve this could be render-time variables. These can be used in queries, like in this test: https://github.com/mapnik/python-mapnik/blob/master/test/python_tests/postgis_test.py#L1250-L1253 There is python call render_with_vars(): https://github.com/mapnik/python-mapnik/blob/master/src/mapnik_python.cpp#L829-L837 But it is not much tested and documented.

[giantchen2012]

Alright, you mean I can first get the datasource from postgis, then apply styles in an existing map xml to this layer, am I right? If so, I'll try it out. And thanks again.