Render my map in Mapnik

Question

Sorry for disturbing. I cannot render my map, I don't know why...

I read a csv file using ogr, which use a .vrt file I created, associated to the csv:

Then, I have a simple code to render my map, but I cannot it work: a map with an empty background is created, nothing on it ...

I get a warning, but I think it is normal:

Warning 1: The 'LON' and/or 'LAT' fields of the source layer are not declared as numeric fields,
so the spatial filter cannot be turned into an attribute filter on them

Do you have an idea ?

Thanks!

My .csv (called ZZZ.csv), just the begining and the interesting fields:

RecordID,VehId,DateTime,LAT,LON
0,2232,2012-04-07 18:54:39,32.801926,-116.871742
0,2232,2012-04-07 18:54:40,32.801888,-116.871727
0,2232,2012-04-07 18:54:41,32.801849,-116.871704

My .vrt:

<OGRVRTDataSource>
<OGRVRTLayer name="ZZZ">
    <SrcDataSource>ZZZ.csv</SrcDataSource>
    <GeometryType>wkbPoint</GeometryType>
    <LayerSRS>WGS84</LayerSRS>
    <GeometryField encoding="PointFromColumns" x="LON" y="LAT"/>
</OGRVRTLayer>
</OGRVRTDataSource>

My python module to render the card: """module mapniktest"""

import mapnik
#Defining the envelope
MIN_LAT = 30
MAX_LAT = +35
MIN_LON = -120
MAX_LON =-110
MAP_WIDTH = 1000
MAP_HEIGHT = 500

#defining the datasource: the .vrt above
datasource = mapnik.Ogr(file="ZZZ.vrt",layer = "ZZZ")

#Creating layer, rules and styles
layer = mapnik.Layer("ZZZ")
layer.datasource = datasource
layer.styles.append("LineStyle")
stroke = mapnik.Stroke()
stroke.color = mapnik.Color("#008000")
stroke.add_dash(50, 100)
symbol = mapnik.LineSymbolizer(stroke)

rule = mapnik.Rule()
rule.symbols.append(symbol)
style = mapnik.Style()
style.rules.append(rule)
print style

#creating the map
map = mapnik.Map(MAP_WIDTH, MAP_HEIGHT, "+proj=longlat +datum=WGS84")
map.append_style("LineStyle", style)
map.background = mapnik.Color("#8080a0")
map.layers.append(layer)

#displaying the map
map.zoom_to_box(mapnik.Envelope(MIN_LON, MIN_LAT, MAX_LON, MAX_LAT))
mapnik.render_to_file(map, "map.png")

thks!!!!

Answer 1

The problem is that you are applying a LineSymbolizer to point data. You need to either apply a PointSymbolizer or a MarkersSymbolizer to point data.

Also Mapnik 2.1 and above supports reading directly from CSV files so you do not need to use a VRT and the OGR plugin, although both should work similarly.