[Mapnik-users] Draw GPS Points to Map/Image

Andreas Volz lists at brachttal.net
Sun Aug 17 20:58:05 CEST 2008

Am Thu, 07 Aug 2008 11:15:02 +0200 schrieb Ric S:

> Hi folks,
> I have successfully setup mapnik. Generating a map already works.
> Now I would like to draw gps points into the map, I was searching the 
> net for a few hours to get some info, unfortunately
> I still have now clue yet how this can be done with mapnik.
> I assume I have to create a layer and add points to it. I could not
> find an example how to draw points.
> I would like to set gps points in my map. Could you please show me
> how to add a single gps point to this map/layer. The code from
> generate_image which I used:
> ...
>     z = 10
>     imgx = 100 * z
>     imgy = 100 * z
>     m = Map(imgx,imgy)
>     load_map(m,mapfile)
>     prj = Projection("+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 
> +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs
> +over") c0 = prj.forward(Coord(ll[0],ll[1]))
>     c1 = prj.forward(Coord(ll[2],ll[3]))
>     bbox = Envelope(c0.x,c0.y,c1.x,c1.y)
>     m.zoom_to_box(bbox)
>     im = Image(imgx,imgy)
>     render(m, im)
>     view = im.view(0,0,imgx,imgy) # x,y,width,height
>     view.save(map_uri,'png')

I've done that some time ago. Worked well. But then I deactivated the 
code for some reason. Not sure if it works at the moment:

void MapnikSource::insertDataPoint (double x, double y, const char *key, const char *value, const char* layer)
  /*Layer lyr (layer);
  datasource_ptr ds (new mapnik::memory_datasource);
  feature_ptr f (feature_factory::create (keyID));

  geometry_ptr point (new point_impl (-1));
  point->move_to (x, y);


  transcoder tr ("utf-8");
  (*f)[key] = tr.transcode (value);
        if (ds)
                mapnik::memory_datasource *mem = dynamic_cast <mapnik::memory_datasource*> (ds.get ());
                if (mem)  // check if cast is ok!
                        // do something with memory_datasource e.g. push some features
                        mem->push(mapnik::feature_ptr(new mapnik::Feature(-1)));
                        mem->push (f);
  lyr.set_srs ("+proj=latlong +datum=WGS84");
  lyr.add_style ("enigator");
  map->addLayer (lyr);

This is how I called it:

m_mapnikSource.insertDataPoint (x, y, "enigator", "wptred", "enigator");

This is the reference in the XML file:

  <Style name="enigator">
      <PointSymbolizer file="/home/andreas/src/svn/enigator/trunk/data/symbols/wptred.png" type="png" width="32" height="32" />

Search the history of this list with my name and around 10-12 month ago or so.
Maybe this helps you...


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