2009/5/14 Rahkonen Jukka <[email protected]>: > Hi, > > I do not know TTF image format but if is behaves like TIFF then I can have a > try. > > 1) Build overviews for the big image. Gdal program gdaladdo can make it > for the image formats it is supporting. It means in practise that high > resolution image is subsampled to bigger pixel sizes. Overviews can be > internal (subsampled, so called pyramid layers are written inside of the > image file) ot they can be external. Program supporting overviews is > picking the right resolution level automatically for rendering. I do not > know if Mapnik supports overviews but it is possible because it is using > gdal.
Mapnik doesn't support overviews (yet?): http://trac.mapnik.org/ticket/54 > > 2) Make a static subsampled image(s) to be used in Mapnik rendering when > zoomed out. Gdal_translate can make those. > I use this aproach for hillshading. I have 16020x14221 file 218MB size and two scaled versions (50%x50% and 25%x25% of original size): http://mapa.ump.waw.pl/ump-www/?zoom=10&lat=49.05284&lon=19.93777 Also for testing I tried bigger files, up to 1.1GPix size: https://lists.berlios.de/pipermail/mapnik-users/2009-April/001747.html For files >4GB You need gdal and mapnik compiled with bigTiff support. If using big tiff's, You need to take special care for resizing/scaling in mapnik. If You try to downscale (ie one tile 256x256 covers 10000x10000pix of source tiff), means mapnik need enough memory for this big source image. But if scaling is reasonable (ie 512x512 raster -> 256x256 tile), memory consumption isn't problem, because mapnik reads only part of tiff file needed to render actual region (metatile). So in practice, it is best to have separate raster for each zoom with resolution same as this zoom level. If resolution isn't the same as mapnik resolution at any zoom level, then when upscalling (ie 64x64 raster fragment -> 256x256 mapnik tile) tiles wouldn't be alignment: joining will be visible. Using multiple adjacent files to cover large area is also possible, as I described in mentioned thread and here: http://trac.mapnik.org/ticket/295 There are still possible some artifacts when upscaling due to interpolation problems as described in ticket (see examples), but when using simple raster drawing (not composing), it is enough to have at least few pixel overlapping and drawing slices in right order (not sure, probably define datasources for slices in left->right, up->down order). Still using same resolution as one of mapnik zoom levels is important or rounding errors will introduce misalignment when up/downscalling. > 3) Build tiles for the slippy map directly with MapTiler program > (http://maptiler.org). It is a nice piece of software and worth a try at > least. > I would recommend this for raster only layer, as mapnik doesn't need to draw anything on it so why not to use tools specialized for this task. Using mapnik is needed, when You would like to draw something on this raster, i.e. us it as background for vector map (nontransparent) or hillshading like in my case. > ________________________________ > Lähettäjä: [email protected] > [mailto:[email protected]] Puolesta Alireza Kashian > Lähetetty: 14. toukokuuta 2009 11:24 > Vastaanottaja: [email protected] > Aihe: [Mapnik-users] Rendering satellite imagery as a layer for hybridview > in mapnik > > Hi. > > My last question about PNG compression was answered perfectly. thanks to all > responders. > > One of the things we are trapped in is satellite view for our slippy map.( > we want to have hybrid) > > We got the files from quickbird satellite in TTF (GeoRefrenced). like 700 > Square Km. > > The whole city is like 18 Gigabyte in Size. I mean the size of single > colorful TTF file. > > We tested mapnik against that big TTF file and used the GeoRefrenced TTF as > a source for mapnik layer. > > The problem is the size of TTF when mapnik wants to make a tile in a > specific zoom. We have 8 GIG of ram in Debian, but still we are in lack of > memory. > > I think mapnik tries to open up the TTF file, but since it is so much big, > it fails. it is logical. > > The solution would be slicing the TTF into smaller files. We tried even with > 1 GIG files, but still fails. > > so my question is that : What is the technique for rendering satellite > imagery when you handle large ttf files. If the answer is slicing, then what > happens to edges between two tiles when one part is in TTF1 and the second > part is in TTF2...how can we tell mapnik to use which TTF file...things are > a bit vague..how many slices we should make ! > > thanks > Alireza > > _______________________________________________ > Mapnik-users mailing list > [email protected] > https://lists.berlios.de/mailman/listinfo/mapnik-users > > -- Marcin Rudowski _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users
