Python class which uses mapnik to create a static map based upon a coordinate.

gistfile1.py

import mapnik
from shapely.geometry import *

class StaticMap:

    srs = '+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 +wktext  +no_defs'
    wgs = '+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs'
    stylesheet = 'REA_Bright_Local.xml'
    markername = 'rea.png'
    exportpath = 'output/'
    imagetype = 'png'
    longlat = mapnik.Projection(wgs)
    merc = mapnik.Projection(srs)
    m = mapnik.Map(500, 500,srs)

    def __init__(self, stylesheet):       
        self.stylesheet = stylesheet        

        #initialise the map
        mapnik.load_map(self.m, stylesheet)
        
        #set up the icon
        self.createMarkerStyle()

    def transformToWebMercator(self, x, y):

        coord  = mapnik.Coord(y,x)
        transform = mapnik.ProjTransform(self.longlat,self.merc)
        return transform.forward(coord)

    def createMarkerStyle(self):

        s = mapnik.Style()
        r = mapnik.Rule()
        sym = mapnik.PointSymbolizer(mapnik.PathExpression(self.markername))
        r.symbols.append(sym)
        s.rules.append(r)
        self.m.append_style('point_style',s)

    def createMap(self, id, x, y):

        #tranform the input wgs84 coord to web mercator and create WKT
        transformedCoord =  self.transformToWebMercator(float(x),float(y))
        wkt =  "POINT("+str(transformedCoord.x)+" "+str(transformedCoord.y)+")"

        #buffer the point to give us an envelope to zoomm to.
        shapelyPntBuffer = Point(transformedCoord.x, transformedCoord.y).buffer(600.0)
        e = mapnik.Box2d(float(shapelyPntBuffer.bounds[0]),float(shapelyPntBuffer.bounds[1]),float(shapelyPntBuffer.bounds[2]),float(shapelyPntBuffer.bounds[3]))

        #add feature to memory data source
        ds = mapnik.MemoryDatasource()
        f = mapnik.Feature(mapnik.Context(), int(id))
        f.add_geometries_from_wkt(wkt)
        ds.add_feature(f)

        #create a mapnik lyr and set it's datasource to be our memory datasource.
        icons = mapnik.Layer('icons',self.srs)
        icons.datasource = ds
        icons.styles.append('point_style')
        self.m.layers.append(icons)

        #reset the map extent and export
        self.m.zoom_to_box(e)
        mapname = self.exportpath+str(id)+"."+self.imagetype
        mapnik.render_to_file(self.m,mapname, self.imagetype)

        #dump the icons layer
        self.m.layers.__delitem__(29)

        return str(id)+"."+self.imagetype

Any reason why m = mapnik.Map(500, 500,srs) is in the class declaration rather than the initialiser? I can see you adding tonnes of layers to the same map by calling StaticMap() a few times.

What's the output you're seeing?

I create a single instance of the StaticMap class - but yes m = mapnik.Map(500, 500,srs) should be in the init. What I'm seeing is that the icons layer gets added\removed each time I call createMap on the the StaticMap instance - which is what I want, but on some calls the layer does not render, on others it does.

Can you give me a list of example datapoints? Nothing near the anti-meridian?

I presume you're using mapnik 2.1? Linux?

-31.896665 152.497463
-37.564001 143.834026
-37.856527 145.236776
-29.3149959 151.6941479
-33.744679 150.910469
-37.812278 144.886932
-37.848785 144.66121
-38.3827659 142.4844995
-33.968852 151.104412
-35.357152 145.730707
-27.5510948 153.036698

• mapnik version: 2.1.0
• seen the issue on OS X 10.7.5
• seen the issue on Ubuntu 12.1