April 29, 2012
Maperipy sample: generate tiles and then optimize with OptiPNG

The latest (2.0.28) Maperitive beta now comes with a sample Python script showing how you can override the default behavior of Maperitive tile generation process. The sample collects the generated tile files and then executes OptiPNG on them to reduce the file size (OptiPNG is now included in Maperitive package) of PNGs.

Some more info about this release: http://groups.google.com/group/maperitive/browse_thread/thread/492671b461f1e1da

Here’s the source for the sample, I think it’s self explanatory:

from maperipy import App
from maperipy import Map
from maperipy.webmaps import Tile
from maperipy.tilegen import TileGenCommand

def func1 (zoom, x, y, tiles_horizontal, tiles_vertical):
    # Demonstrates how to control which tiles get rendered
    # note that Maperitive generates tiles in batches
    # (defined by tiles_horizontal x tiles_vertical count).
    # So for example, 3x3 (=9) tiles are generated in a single bitmap 
    # and then later they are split into individual tiles.

    # In this case we just print some info to Maperitive's command log window.
    print "Generating tile batch: {0}/{1}/{2} ({3}x{4} tiles)" \
        .format(zoom, x, y, tiles_horizontal, tiles_vertical)

    # In this case we return True to signal that we want 
    # these tiles to be rendered.
    return True

def func2 (tile):
    # Demonstrates how to control the saving of a tile to disk.
    # At this point we could do some postprocessing of the tile bitmap
    # or store it somewhere else (and then return False to prevent
    # Maperitive from saving it to the default location).
    print "Saving tile: {0}/{1}/{2} (file: {3})" \
        .format(tile.zoom, tile.tile_x, tile.tile_y, tile.file_name)

    # You could, for example, store tiles into a database instead
    # of writing them to disk.

    # In this case we return True to signal that we want 
    # the tile to be saved to the default location.
    return True    

def optimize_tiles():
    args = []

    # Turn on backup files (just to compare sizes with optimized tiles).
    #args.append ("-backup")

    # Set the OptiPNG optimization rate (0 to 7), 7 being very slow.
    optimization_rate = 2
    args.append ("-o{0}".format(optimization_rate))

    # We don't want any OptiPNG output text to clutter Maperitive.
    args.append ("-quiet")


    # This is one way to execute external programs.
    App.run_program("tools/OptiPNG/optipng.exe", 100, args)

    # Clear the list.
    del tiles_to_optimize[:]

def collect_tiles (file_name):
    # Demonstrates how to collect the list of generated tiles.
    # You could, for example, use this function to upload
    # tiles to a Web server.

    # In this case we collect the file names to a list...

    # ... and then we call OptiPNG when the list gets full.
    if len(tiles_to_optimize) >= 10:

tiles_to_optimize = []

# Generate tiles for the currently set geometry bounds and the current zoom level
# (Map.position.zoom, Map.position.zoom) -> min.zoom, max.zoom
cmd = TileGenCommand(Map.geo_bounds, Map.position.zoom, Map.position.zoom)

# This is how we override TileGenCommand with custom functions.
cmd.tile_generation_filter = func1
cmd.tile_save_filter = func2
cmd.after_tile_save = collect_tiles


# Run the optimization again for any left-over tiles.