3

I have a folder of sea maps in S57 format (i.e. file.000 files). And I want to create a .png at some location as input. So my tools are: old debian-based OS, S57 as map format, navi2pg or ogr2ogr to parse maps into database, GDAL version 1.10.1, PostgreSQL+PostGIS to hold the maps and mapnik to render PNG. I use navi2pg https://github.com/nextgis/navi2pg like this

$ ./navi2pg --schema public PG:"host=localhost user='user' password='useruser' dbname=testdb port=5433" ./map_file.000 ./templates/mapserver.map.template ./templates/mapnik.xml.template ./templates/mapnik.py.template

What it does is parse the map file to db and generates 3 files: mapserver file, which I don't need, .xml file (which is needed for mapnik) and .py file, see below, which I can launch with Python to create a PNG picture. All is good, but the problem is I can't use it, or I don't know how, for multiple map files, it shows an error that layer is already exists and exits when I try it. I tried to tinker code a bit but I did not succeed.

I use ogr2ogr like this

$ ogr2ogr -skipfailures -append -update -s_srs "+init=epsg:4326" -f PostgreSQL PG:"host=localhost user='user' password='useruser' dbname=testdb port=5433" ./map_file.000

it parses map to db and you can use -append to write more to existing tables, as far as I understand. But the problem is I don't have the .xml file that has rules how to render the picture with mapnik. I tried to change the XML file that comes from navi2pg but I failed again, because ogr2ogr and navi2pg put the map into the db differently, not only different names, but structurally as well; in ogr2ogr all layers have different tables, in navi2pg they are grouped in some way. Also I am not exactly sure if I was doing the right thing. I checked both databases in QGIS and they look the same, so no question about the db part for one file. When I have the db and XML ready, I want to use mapnik.py, it doesnt have location input, it just creates a PNG from the map:

import mapnik

m = mapnik.Map(1024,1024)
m.background = mapnik.Color('steelblue')
mapnik.load_map(m, 'file.mapnik.xml')

extent = mapnik.Box2d(2.914476e+06, 8.260046e+06, 3.131549e+06, 8.531149e+06)

m.zoom_to_box(extent)

mapnik.render_to_file(m,'file.mapnik.png', 'png')
print "rendered image to 'file.mapnik.png'"

This creates a picture with the whole map in 1024x1024. I can later add arguments and change the extent with location and scale and have different parts of map on PNG.

Additional problem comes with Box2d arguments, when I use navi2pg it generates the min and max sizes and I can understand the size of map. and I can't understand how it does it, and these are not geo coords. I found a PostGIS function ST_EstimatedExtent postgis.net/docs/ST_EstimatedExtent.html and it looks like something I need, but I can't understand on which column to use it.

3
  • I think I can use ogr2ogr to get my db into geojson file, which I can use for mapnik as well. I will look into this.
    – ygroeg
    Commented Aug 26, 2021 at 5:24
  • No, mapnik::map.load_map(...) doesn't work with not xml files.
    – ygroeg
    Commented Aug 26, 2021 at 11:56
  • I believe the way to go is to create my own xml file with style rules and with resources for it if needed.
    – ygroeg
    Commented Aug 26, 2021 at 13:17

1 Answer 1

0

The solution i used - write the XML file myself. After i decided what layers i will need for final picture, i used templates and adapted them for my case.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.