[Tilecache] Tile seeding hardly slow down after projection

[Damiano Morosi]

Hi,

I was using the following configuration for tilecache:

--

[cache]
base = /tmp/tilecache
type = Disk

[basic]
type=Mapnik
mapfile=/var/www/mapfile.xml
srs = EPSG:4326

#---------------------#
# Impostazione regione#
#---------------------#

bbox = 9.7,39.7,15.3,45.3
size=600, 600
resolutions =
0.0093333330,0.0046666665,0.0023333332,0.0011666666,0.0005833333,0.0002916667,0.0001458333,0.0000729167,0.0000364583,0.0000182292,0.0000091146

--

Now, I've projected all the shapes with ogr2ogr using with the following:

+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0
+k=1.0 +units=m +nadgrids=@null +no_defs

that should be the projection used by Google.
So I changed the tilecache config:

--

[cache]
base = /tmp/tilecache-proj
type = Disk

[basic]
type=Mapnik
mapfile=/var/www/mapfile-proj.xml
srs = +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0
+y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs

#---------------------#
# Impostazione regione#
#---------------------#
bbox = 1079799,4936842,1703799,5560842
size=600, 600
resolutions =
1040.0000000000,520.0000000000,260.0000000000,130.0000000000,65.0000000000,32.5000000000,16.2500000000,8.1250000000,4.0625000000,2.0312500000,1.0156250000

--

and, of course, the mapnik mapfile. Now the tilecache_seed.py is taking
about 0.9 seconds for generating a single tile, while before this
modification the time required was about 0.02 s. All the shapes are indexed
with shapeindex on 64 levels. It's possible that a change in the projection
cause such a dramatical performances decrease? Or maybe tilecache is trying
to "reproject" something?

Thank you all,

Damiano
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