Hi Nick, Between 0.7 and 0.7.1 png quantization received some fixes to support alpha in png256 output, but there were also a few edge cases subsequently fixed in trunk (now released mapnik2).
I see in your code you are using gd to combine images. Maybe try writing out the Mapnik image as full color png? Dane --- \o/ --- Sent from my phone On Oct 16, 2011, at 5:33 AM, Nick Whitelegg <nick.whitel...@solent.ac.uk> wrote: > Hi, > > I *think* this happened when I upgraded Ubuntu from 10.04 to 10.10 back in > March, and I *think* previously I was using a version of mapnik compiled from > source whereas now I use the standard ubuntu package. I know that was a long > time ago - but I'm only now getting back to this project. > > But anyway.. I'm trying to render Ordnance Survey Land Form Panorama contours > using mapnik, with the aim of compositing them with OS VectorMapDistrict > raster tiles and OSM footpath data. The contours are stored in a postgis > database. I have a custom C++ application which renders the contours with > mapnik, and then composites them with the Vector Map District using gd. > > The problem is that mapnik (0.7.1 with ubuntu 10.10) appears to only render > the contours as a 4-bit images, and unantialiased, which means the contours > don't look great. The same version of mapnik renders OSM data fine (256 bit > pngs) and, on a previous run, (which I think was before I upgraded the OS, > and was using Ubuntu 10.04 with - IIRC - a compiled-from-source version of > Mapnik) the contours were rendered as antialiased 8-bit images too. > > To see what I mean see > > http://www.free-map.org.uk/expts/vmdlfp200/index.php?e=400000&n=149000 > > and compare the contours to the east of that position (higher quality) and to > the west (lower quality). The area to the west was rendered later, with the > current setup. > > Occasionally the contour lines are not coloured at all and just render black! > (e.g. just to the N of the position above). > > The source code of the application is at > http://www.free-map.org.uk/svn/freemap/opendata/lfpvmd.cpp > > and map.xml is the accompanying Mapnik XML file. > > Apologies if I'm a bit vague about this, but it was something I was last > working on more than 6 months ago and the time this problem arose was about > the time I upgraded my system. But has anyone else had similar problems, or > recognise the issue? > > Thanks, > Nick > = > _______________________________________________ > Mapnik-users mailing list > Mapnik-users@lists.berlios.de > https://lists.berlios.de/mailman/listinfo/mapnik-users
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