Dane Springmeyer pisze:
> A few more comments inline...
>> For areas bigger then Poland (are there bigger Countries then Poland?
>> ;) ) problem could be aligning separate rasters. I use one big tiff
>> (200MB) and gdal should allow much bigger files, but I'm not sure if
>> mapnik does.
>
> Mapnik currently does not support using GDAL overviews, so that may help
> with larger files:
>
> http://trac.mapnik.org/ticket/54
I didn't mean any overviews, but using "tiling" to cover large or
irregular areas. Now I use one big square tiff, but i.e. when trying to
cover Europe, there is much of space wasted for water.
For less detailed zoom's I use separate rasters (0.5x0.5 and 0.25x0.25
of original one).
I recently played for fun with 3-4x bigger area then my actual
settings and had no problems, so if storage isn't a problem, i.e. Europe
hillshading could be covered with one big file. If gdal can handle file,
mapnik too. I haven't tested aligning two adjacent rasters yet.
My first experiment is 830MPix tiff, 790MB size after converting
srtm3 -> hillshaded raster, described in earlier email:
Raster size: 36 410 x 22 770
Upper Left ( -46.383, 7361946.980) ( 0d 0'1.50"W, 55d 0'1.50"N)
Lower Left ( -46.383, 5621476.490) ( 0d 0'1.50"W, 44d59'58.97"N)
Upper Right ( 2783024.787, 7361946.980) ( 25d 0'1.21"E, 55d 0'1.50"N)
Lower Right ( 2783024.787, 5621476.490) ( 25d 0'1.21"E, 44d59'58.97"N)
Its quite big part of Europe. After demtool, output tiff is 800MB size,
however middle step file (warped.tif from my "instruction") is 3.1GB.
All processing, but without "nodata" holes filling, took ~1.5h on 3
years old laptop (Mobile AMD 2.2GHz). Mapnik reads this big file with no
difference to Poland only file, as tiff format allows reading
interesting part of the image without reading whole file.
If any file is >4GB then gdal needs to be compiled with
BigTIFF support: libtiff with BigTiff or gdal compiled using
--with-libtiff=internal. Otherwise You get:
> Creating output file that is 36411P x 30740L.
> ERROR 6: A 36411 pixels x 30740 lines x 1 bands Float32 image would be larger
> than 4GB but this is the largest size a TIFF can be, and BigTIFF is
> unavailable.
> Creation failed.
To allow mapnik to open rasters >4GB it should be compiled against
gdal library with enabled BigTIFF support. But 4GB hillshading file
means 4GPix raster !!! which isn't that abstract if trying to cover
any continent as one rectangle. Not to mention srtm1 in America.
Another partial solution would be adding -co "COMPRESS=LZW" or similar
to gdal_warp, but it gives only little size reduction.
I also tried compression in demtool by adding:
papszOptions = CSLSetNameValue( papszOptions, "COMPRESS", "LZW" );
in hillshade.cpp. Output shaded file decreased from 1070GB to 712MB for
36411x30740 raster, 1.1GPix (!!!) tiff:
Raster size: 36 411 x 30 740
Upper Left ( -46.383, 7361946.980) ( 0d 0'1.50"W, 55d 0'1.50"N)
Lower Left ( -46.383, 5012273.600) ( 0d 0'1.50"W, 40d59'58.34"N)
Upper Right ( 2783101.224, 7361946.980) ( 25d 0'3.69"E, 55d 0'1.50"N)
Lower Right ( 2783101.224, 5012273.600) ( 25d 0'3.69"E, 40d59'58.34"N)
There was only little time increase when generating map with mapnik
using compressed tiff (<10%)
I tried using two rasters, but fixing mapnik was needed:
http://trac.mapnik.org/ticket/295
>> BTW. as for big tiffs, I have some problems with segmentation faults.
>
> Interesting. Marcin, could you post details of this to a trac ticket?
http://trac.mapnik.org/ticket/294
Marcin Rudowski
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