Thanks Rahkonen and Rudowski.. Yes.. we are not actually drawing anything on satellite imagery tiff, so we probably may not need Mapnik in this case.
I checked maptiler, but may be I am still walking on a wrong path. In our tilecache config our MaxResolution = 61 ---- We are using UTM coordination. Mapnik generates tiles for us. But: How can I be sure that if I use Maptiler or any other tile cutter, it exactly slices the TIFF file inline with mapnik tiles that I have already cached even if both are on same resolution...how can I set the slicing edge to be matched exactly with Mapnik edge...since it is hybrid view, both must be exactly matched on top of each other... How can I find the correction resolution for each mapnik zoom level which is requested by OpenLayers...does it report somewhere I can see it? or I have to cacluate it myself? At the moment, I see openlayers does generate the BBOX and asks mapnik to generate tile for us.. so it should be openlayer who decides each tile corners starts from point X1 and ends in Point X2 .. thanks Alireza On Thu, May 14, 2009 at 1:55 PM, Marcin Rudowski <[email protected]>wrote: > 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 >
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