Hash from --get-hash does not match the one detected while generating empty tiles

[asaunier]

The following command returns a hash for empty_tile_detection:

$ ./buildout/bin/generate_tiles --get-hash 0/8/8 -l grundkarte 
Tile: 0/8/8:+8/+8    
    empty_metatile_detection:
        size: 753
        hash: 7227e6229574d56f9d02ec3f71064ee717dfeea1
Tile: 0/8/8
    empty_tile_detection:
        size: 1189
        hash: cddcea030117de8845ebb2a7e98fa2cdad301f13

that does not match the one actually computed when generating empty tiles with

./buildout/bin/generate_tiles -l grundkarte -z 0 -v

(should be f94e1d96bda53402b0b4f0a2d74b9ea37ab1f17a).

The error occurs with the PNG tiles, OK with JPEG tiles.

Here is the relevant parts of the config.yaml file:

ayer_default:
    type: wms
    grid: swissgrid
    # The minimum resolution to seed, useful to use with mapcache, optional.
    min_resolution_seed: 0.25
    # the URL of the WMS server to used
    url: http://${vars:host}/${vars:instanceid}/wsgi/mapserv_proxy
    # file name extension
    extension: png
    # the bbox there we want to generate tiles
    bbox: [669000, 193000, 722000, 232000]

    # mime type used for the WMS request and the WMTS capabilities generation
    mime_type: image/png
    wmts_style: default
    # the WMTS dimensions definition [default to []]
    dimensions:
        -   name: DATE
            # the default value for the WMTS capabilities
            default: 2013
            # the generated value
            value: 2013
            # all the available values in the WMTS capabilities
            values: [2013]
    # the meta tiles definition [default to off]
    meta: on
    # the meta tiles size [default to 8]
    meta_size: 8
    # the meta tiles buffer [default to 128]
    meta_buffer: 128
    # connexion an sql to get geometries (in column named geom) where we want to generate tiles
    # Warn: too complex result can slow down the application
#    connection: user=www-data password=www-data dbname=<db> host=localhost
#    sql: <column> AS geom FROM <table>
    # size and hash used to detect empty tiles and metatiles [optional, default to None]
    empty_metatile_detection:
        size: 753
        hash: 7227e6229574d56f9d02ec3f71064ee717dfeea1
    empty_tile_detection:
        size: 1189
        #hash: cddcea030117de8845ebb2a7e98fa2cdad301f13
        hash: f94e1d96bda53402b0b4f0a2d74b9ea37ab1f17a

layers:
    grundkarte:
        layers: grundkarte
    ortho:
        layers: ortho
        extension: jpeg
        mime_type: image/jpeg
        # no buffer needed on rater sources
        meta_buffer: 0
        empty_metatile_detection:
            size: 66163
            hash: a9d16a1794586ef92129a2fb41a739451ed09914
        empty_tile_detection:
            size: 1651
            hash: 2892fea0a474228f5d66a534b0b5231d923696da

[ochriste]

do you remember if for your png you had any QUANTITIZE_* options set in the mapfile's OUTPUTFORMAT for png ?

[sbrunner]

The optimize=True in image save options (purpose in #172) don't do anything ...

Adding image = image.convert(mode='P', palette=Image.ADAPTIVE) in the metatile spliter solved the issue but it's an unwanted hack, I will see for an other solution...

[sbrunner]

I hope that process (available in version 0.8) will be a solution to fix that ...

E.g.:

layers:
  <name>:
    post_process: optipng

process:
    optipng_test:
    - cmd: optipng -o7 -simulate %(in)s
    optipng:
    - cmd: optipng %(args)s -zc9 -zm8 -zs3 -f5 %(in)s
        arg:
            default: '-q'
            quiet: '-q'