Hi guys, I am new to mapnik and just stumbled on this problem today. I am in the same situation of trying to render the sea on top of color relief/hillshading layer so I was wondering if you ever got this to work. Googling around haven't helped me much on this problem so any help would be much appreciated.
Cheers, David > Tue Jan 12 14:31:08 CET 2010 Philip Howarth <Philip at Howarth.name> > > Many thanks Andy, > > You have pretty much confirmed what I was beginning to believe - that I > needed to do some processing with the processed_p. Your idea of inverting it > is simple (in concept) - so simple I hadn't thought of it! I was mentally > doodling all sorts of things involving using processed_p shapes as a mask > and doing some mildly complicated image processing with them on the > relief/hillshade tiffs. > > There is no panic, so I'd be happy to wait for your new improved sea polygon > data set. > > Thanks for confirming that I wasn't quite as crazy as I was beginning to > fear! > > Regards, > > Philip > > > 2010/1/12 Andy Allan <gravitystorm at gmail.com> > > > On Wed, Dec 30, 2009 at 1:20 PM, Philip Howarth <Philip at howarth.name> > > wrote: > > > Is anybody able to offer some ideas on how to render > > > hillshading/colour-relief in areas with coastline? > > > > Hi Philip, hopefully I can help. > > > > > I have used the methods described in the OSM wiki and elsewhere to get > > nice > > > colour-relief tiffs. I can render images using these so long as I put the > > > layer(s) containing the tiffs first. > > > > > > The problem comes around the coastline. I think that I really need to > > paint > > > the coastline using the processsed_p shape file (as the images produced > > from > > > the SRTM data aren't good enough to define the coastline - especially > > with > > > low lying islands). > > > > Beyond that in fact - it's impossible given that parts of the UK > > (around the Wash) and especially the Netherlands are below sea level > > in SRTM. I've seen naive attempts to make a zero-elevation blue before > > :-) > > > > > Clearly, if I just paint a filled coastline on top of > > > the hillshade, I lose the hillshade and vice versa. > > > I've tried lots of things but without the success that Opencyclemap have > > > clearly achieved. > > > > > http://www.opencyclemap.org/?zoom=12&lat=55.65104&lon=-1.85604&layers=B000 > > > The best I've achieved is to use the linesymbolizer to draw round the > > > coastline shapes rather than fill them - but this is both a bodge and it > > > inevitably draws spurious lines. See: > > > http://www.philip.howarth.name/NorthumberlandRelief2.png If anyone is > > able > > > to give me some pointers, I'd be very grateful. > > > > There are two options I can recommend. > > > > 1) If you only use hillshading, then you can use mapnik's image > > compositing (as of 0.6). Use the normal coastline file as your first > > layer, and then a rastersymbolizer layer with a hardlight compositing > > option to blend in your hillshading tiffs. It works, but you get > > slight artefacts near the coasts since the hillshading isn't being > > clipped. > > 2) If you need colour relief, or accurate clipping, then you need an > > inverted coastlines file. I have a patch to an old version of the OSM > > coastline generator to make sea polygons instead of land polygons, and > > I'm in the process of updating it to work with newer versions of the > > coastline generator. Give me a week or so and it should be finished. > > Unfortunately the latest inverted coastline shapefile I have is from > > Feb 2009, and it's showing its age. I should have a new one soon too. > > > > Hope this helps, > > Andy > > > > > Just to make it harder... I'm using WIndows. > > > > > > Philip > > > -- > > > Philip Howarth > > > Cambridge UK > > > email: Philip at Howarth.name > > > > > > _______________________________________________ > > > Mapnik-users mailing list > > > Mapnik-users at lists.berlios.de > > > https://lists.berlios.de/mailman/listinfo/mapnik-users > > > > > > > > > > _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users
