kueda.net » google maps http://kueda.net I'm Back Thu, 02 Feb 2012 19:42:04 +0000 en hourly 1 http://wordpress.org/?v=3.3.1 Using MySQL lat/lon Columns as a Mapnik Datasource http://kueda.net/blog/2009/05/04/mysql-as-mapnik-datasource/ http://kueda.net/blog/2009/05/04/mysql-as-mapnik-datasource/#comments Mon, 04 May 2009 05:07:28 +0000 Ken-ichi http://kueda.net/?p=259 With the gracious help of Dane Springmeyer, I recently got Mapnik up and running on my Mac, so naturally the first thing I wanted to do was to plot iNaturalist observations. Mapnik will talk with a PostGIS database just fine, but it wont’t pull points from a MySQL database table, at least not directly. What it does support, though, is the all-powerful OGR. Back when I used to use Mapserver, I had used OGR a few times to act as a bridge between simple lat/lon columns in a MySQL table and Mapserver (great description here), so I figured the same would be possible in Mapnik.


First Hurdle: Getting Mapnik to Show Anything At All

First I made an OVF file so OGR would know how to talk to my database:

<OGRVRTDataSource>
  <OGRVRTLayer name="observations">
    <SrcDataSource>MYSQL:inaturalist_development,user=root,tables=observations</SrcDataSource> 
    <SrcSQL>SELECT id, latitude, longitude, iconic_taxon_id FROM observations</SrcSQL> 
    <GeometryType>wkbPoint</GeometryType>
    <GeometryField encoding="PointFromColumns" x="longitude" y="latitude"/> 
  </OGRVRTLayer>
</OGRVRTDataSource>

and made sure it was working:

mapnik-inat > ogrinfo inat.ovf
ERROR 4: Update access not supported for VRT datasources.
Had to open data source read-only.
INFO: Open of `inat.ovf'
      using driver `VRT' successful.
1: observations (Point)

Then I basically modified the Mapnik tutorial to use the OGR virtual data source:

import mapnik
 
# Setup the datasource and layer
ds = mapnik.Ogr(file="inat.ovf", layer="observations")
lyr = mapnik.Layer('test lyr')
lyr.datasource = ds
 
# Style the points using a simple PNG
m = mapnik.Map(600, 300, "+proj=latlong +datum=WGS84")
s = mapnik.Style()
r = mapnik.Rule()
symbolizer = mapnik.PointSymbolizer('mm_8_stemless_iNatGreen.png', 'png', 8, 8)
symbolizer.allow_overlap = True
r.symbols.append(symbolizer)
s.rules.append(r)
m.append_style('My Style', s)
lyr.styles.append('My Style')
m.layers.append(lyr)
 
# Zoom to the extent of the data and write the map to a PNG
m.zoom_to_box(lyr.envelope())
mapnik.render_to_file(m, 'test.png', 'png')

And then I got a map!

test

Ok, a kind of crappy map of test data, but actual, real, visible pixels! So much better than arcane error messages!

Second Hurdle: Google

Of course, it’s just a map of some test points, but still, it worked. Yay. Next thing I wanted to do was to see how easy it would be to lay these points over a Google map, since one of the things I’d like to do with Mapnik is have a layer showing ALL observations on the iNat observation browser. Turns out this was a piece of cake using tilelite.

First I put my map configuration in an XML file, adding a bit of complexity using SQL filters to show different markers for different kinds of points (here corresponding to the IDs for different iconic taxa, e.g. plants, animals, fungi, etc.).

<Map srs="+proj=latlong +datum=WGS84">
  <Style name="observationsStyle">
    <Rule>
      <Filter>[iconic_taxon_id] = 47126</Filter>
      <PointSymbolizer file="mm_8_stemless_iNatGreen.png" type="png" width="8" height="8" />
    </Rule>
    <Rule>
      <Filter>[iconic_taxon_id] = 1 or [iconic_taxon_id] = 47178 or [iconic_taxon_id] = 3 or [iconic_taxon_id] = 20978 or [iconic_taxon_id] = 26036 or [iconic_taxon_id] = 40151</Filter>
      <PointSymbolizer file="mm_8_stemless_DodgerBlue.png" type="png" width="8" height="8" />
    </Rule>
    <Rule>
      <Filter>[iconic_taxon_id] = 47115 or [iconic_taxon_id] = 47119 or [iconic_taxon_id] = 47158</Filter>
      <PointSymbolizer file="mm_8_stemless_OrangeRed.png" type="png" width="8" height="8" />
    </Rule>
    <Rule>
      <Filter>[iconic_taxon_id] = 47170</Filter>
      <PointSymbolizer file="mm_8_stemless_DeepPink.png" type="png" width="8" height="8" />
    </Rule>
    <Rule>
      <ElseFilter/>
      <PointSymbolizer file="mm_8_stemless_unknown.png" type="png" width="8" height="8" />
    </Rule>
  </Style>
 
  <Layer name="observationsLayer" srs="+proj=latlong +datum=WGS84">
    <StyleName>observationsStyle</StyleName>
    <Datasource>
      <Parameter name="type">ogr</Parameter>
      <Parameter name="file">inat.ovf</Parameter>
      <Parameter name="layer">observations</Parameter>
    </Datasource>
  </Layer>
</Map>

Then I fired up tilelite:

tilelite > python liteserv.py ~/projects/mapnik-inat/inatmap.xml
Using mapfile: '/Users/kueda/projects/mapnik-inat/inatmap.xml'
Listening on port 8000...

and added a new GTileLayer to my map:

var myCopyright = new GCopyrightCollection();
var allObsLyr = new GTileLayer(myCopyright, 0, 12, {
  isPNG: true,
  tileUrlTemplate: 'http://localhost:8000/{Z}/{X}/{Y}.png'
});
var allObsOverlay = new GTileLayerOverlay(allObsLyr);
map.addOverlay(window.allObsOverlay);

et voila:

Mapnik-rendered observation points on an iNat map.

I have no idea how scalable this kind of solution is, but I just wanted to show that it works. It was my first real experiment with Mapnik, and I’m pretty happy with how simple things were after the decidedly unsimple installation process.

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