On Wed, Dec 30, 2009 at 1:20 PM, Philip Howarth <[email protected]> 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: [email protected] > > _______________________________________________ > Mapnik-users mailing list > [email protected] > https://lists.berlios.de/mailman/listinfo/mapnik-users > > _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users
