Dane, Thanks for your comments. I checked out your 'memory_datasource_polygon' example script. It is no problem to have the geometry I want to add in wkt/wkb as it probably would be anyway coming from shapely or GDAL. So this solution looks good.
It sounds like I have a few choices for generating dynamic layers/geometry in Mapnik: 1 - Upgrade to mapnik2 (trunk) from 1.7.1, figure out how to compile it on windows, and use wkt to create features in a memory data source. 2 - Have Mapnik read a temporary file of JSON/GML/whatever on disk. 3 - Add a sqlite/spatialite layer to Mapnik and adjust the layer to hold the correct features as needed. Does this sound right? I noticed you mention I could create two mapnik images (say base mapping and dynamic mapping) and blend them together (mapnik.Image.blend()). Is there a performance advantage to doing this versus including all layers in one main image? Thanks for the help. Angus --- On Thu, 9/23/10, Dane Springmeyer <[email protected]> wrote: > From: Dane Springmeyer <[email protected]> > Subject: Re: [Mapnik-users] Mapnik for desktop applications > To: "Angus Dickey" <[email protected]> > Cc: [email protected] > Received: Thursday, September 23, 2010, 4:52 PM > > On Sep 23, 2010, at 8:15 PM, Angus Dickey wrote: > > > Hi, > > > > I am new to Mapnik and was thinking about using Mapnik > as the mapping solution for a desktop GIS application. My > initial thoughts were to use: > > > > - Python > > - wxPython > > - Mapnik > > > > Sounds fun! > > > With other packages (OGR/GDAL, Shapely, pyproj, etc.) > if needed. > > Yep. > > > > > I have looked at the Mapnik samples and API and I know > it can make a great looking map, what I am not sure about is > the ability to add a temporary/dynamic layer. > > You have full access in Python for dynamically constructing > both styles and layers. I recommend creating your own > container for them, then pushing them into a mapnik.Map once > you are ready to render. > > You can also have a base set of styles+layers in a > mapnik.Map that is not temporary and then render temp layers > to a different mapnik.Image, then blend the two together > using im.blend(). > > > What I would like to be able to do is have Mapnik set > up with static background mapping data and add markup (or > temp layers) to Mapnik made up of geometry > (points/lines/polys) calculated elsewhere. > > Sort of. It is not yet exposed in Mapnik properly to push > geometries straight into a memory Datasource (only points > are wrapped via PointDatasource), so its easier to read from > disk (even if you create all definitions of the layer on the > fly). > > > Is this possible in Mapnik? I see there are some > provisions for a "Memory Datasource" but it looks like it > only supports points? > > Right. Basically we've been waiting on a proper wkt/wkb > parsing support. > > However, you can actually do this right now if you have > shapely installed, see: > > http://code.google.com/p/mapnik-utils/source/detail?r=1049 > > NOTE: depends on Mapnik trunk. > > > > > Anyone have any thoughts on how this might be done? I > thought about having a text based OGR layer (GeoJSON?) added > to Mapnik and changing this file on disk; doesn't really > seem like a good idea though... > > Its a fine idea and one that is used by nikweb. But yes, it > would feel nicer to push them in dynamically and for now see > the above script and let me know your comments. Alberto > Valverde was the clever Mapnik developer that added the > shapely wkb reading support, which I think is meant to be > temporary but works nicely from my limited tests. > > Dane > > > > > Any info or thoughts are appreciated. > > > > Thanks, > > > > ~Angus > > > > > > > > > > > > > > _______________________________________________ > > 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
