[Marble-devel] Using marble to render PostGIS data in different Projections

Mon Feb 10 12:31:44 UTC 2014

Well I'm actually less interested in rendering than in somehow generating the 
raster inout for my algorithm. Rendering would be a nice benefit later though.

Of course I could do some sort of tiling magic. A single raster would be a lot 
easier though ;-)

plain PostGIS seems to be WKB. It can return the geometries as KML text 
though. I think it won't be that hard to convert this to a GeoLineRing or 
whatever.

I just hope I can work in my desired data dimension. Let me have a try.

Knut

Am Montag, 10. Februar 2014, 13:18:36 schrieb tackat at t-online.de:
> It scales quite well. Actually in Marble master we render the whole "Atlas"
> default map theme using that approach - it has thousands of polygons with
> millions of nodes from the 50m Natural Earth vector data set. And it
> renders that on the fly for every single frame. If you render tenthousands
> of polygons then you will surely have to adjust for that: Couldn't you then
> do the PostGIS database queries dynamically depending on the current
> viewBoundingBox and fill the model dynamically? You would only query a few
> dozens/hundreds polygons for the visible area then. And then unload those
> later and add new ones. If that doesn't work you could have a look at
> Anders' project which rendered OSM vector tiles.
> 
> Oh and another incentive: If you use this approach you can benefit from
> features such as the file view that is available in Marble master and that
> you can see at the bottom left of this screenshot:
> 
> http://byte.kde.org/~tackat/marble_file_view.png
> 
> Of course we are also happy about all patches that improve these features
> further ;-)
> 
> Best Regards,
> Torsten
> 
> 
> -----Original-Nachricht-----
> Betreff: Re: [Marble-devel] Using marble to render PostGIS data in different
> Projections Datum: Mon, 10 Feb 2014 12:54:25 +0100
> Von: Knut Krause <knut.krause at lagom.de>
> An: "tackat at t-online.de" <tackat at t-online.de>, marble-devel at kde.org
> 
> 
> Sure sure.
> 
> btw I should have mentioned, that I plan to use my approach to cover huge
> spaces … like half germany or something like that.
> 
> I hope your suggested approach doesn't run into performance issues too fast
> since that is a fundamental issue here.
> 
> I think I'll render a couple hundred thousand to millions polygons into one
> raster …
> 
> 
> Knut
> 
> Am Montag, 10. Februar 2014, 12:51:26 schrieb tackat at t-online.de:
> > Well I just reread Anders' mail and only now realized that he suggested to
> > export to json and then use the json runner. That would be the lazy
> > approach ;-) (and would probably be less flexible). The beer and pizza
> > invitation is only offered for actually writing the PostGIS runner (where
> > you could borrow code from the existing runners such as the JSON, KML,
> > SHP,
> > and OSM runner).
> > 
> > As a "first shot" you could maybe also have a look at the gpsbabel runner:
> > That one uses the gpsbabel commandline tool - if installed - to convert
> > different file formats to KML and then feeds it to Marble's KML runner.
> > Maybe you could do something similar with the PostGIS database as a source
> > and feed it to the JSON runner. But again that might be less flexible that
> > creating a "full-blown" dedicated "PostGIS" runner.
> > 
> > Oh and in order to test your code (in order to verify your
> > beer-and-pizza-claims ;-))))) ) we need a tutorial on how to use your code
> > - preferably you create a small tutorial at
> > http://techbase.kde.org/Projects/Marble just along the existing ones.
> > 
> > Best Regards,
> > Torsten
> > 
> > 
> > 
> > -----Original-Nachricht-----
> > Betreff: Re: [Marble-devel] Using marble to render PostGIS data in
> > different Projections Datum: Mon, 10 Feb 2014 12:39:20 +0100
> > Von: Knut Krause <knut.krause at lagom.de>
> > An: marble-devel at kde.org
> > 
> > Woah, thanks for your brilliant suggestions.
> > 
> > I'll have a look at the runner and will see how I could use them. If this
> > works for me maybe you'll have to pay for pizza and beer really soon :-P
> > 
> > Knut
> > 
> > Am Montag, 10. Februar 2014, 12:31:06 schrieb tackat at t-online.de:
> > > Hi Knut,
> > > 
> > > I had always wondered why nobody had done this earlier. It should be
> > > relatively straightforward. Ideally you would do it differently though:
> > > Nowadays the GeoPainter approach is too lowlevel. These days we rather
> > > discourage to use GeoPainter directly - although there is nothing bad
> > > about
> > > GeoPainter itself.These days we rather encourage the "object-oriented"
> > > approach. The "object-oriented" approach has lots of benefits and it
> > > should go extremely well with PostGIS:
> > > 
> > > Nowadays Marble imports all files into a single data model: No matter
> > > whether it's KML, GPX, SHP (ShapeFiles) or OSM vector data - all files
> > > get
> > > imported into a single "GeoDataDocument"-document model (we informally
> > > call
> > > that "The GeoData way" since the related classes have the prefix
> > > "GeoData"). The rendering of that model is then done automatically by
> > > GeoPainter behind the scenes. So you don't have to mess with GeoPainter
> > > directly and you don't have to care about the rendering part! This is an
> > > advantage since this is much more convenient for you and also since
> > > GeoPainter might get replaced by an OpenGL-based painter/renderer at one
> > > point. So if you go "the GeoData way" your code will stay future-proof
> > > :-)
> > > 
> > > For importing the PostGIS data into the model you should probably have a
> > > look at the file-import plugins. Yes, each fileformat in Marble is
> > > converted to that single data model via a dedicated plugin. Have a look
> > > inside the source code here:
> > > 
> > > src/plugins/runner
> > > 
> > > In that directory you will find lots of "runners" which create
> > > GeoDataDocuments for various purposes. You probably want to have a look
> > > at
> > > the runners which import the files. Those are inside the subdirectories
> > > kml, gpx, shp, osm. My guess is that the SHP-file is probably most close
> > > to
> > > the PostGIS case. So you can borrow lots of ideas from there. The KML
> > > case
> > > is also very interesting - especially since the structure of our central
> > > universal data-model is inspired by KML. So if you know KML then you
> > > will
> > > get immediately fluent with the GeoData classes since they are named
> > > structured the same way as KML (although they can hold GPX, OSM, SHP and
> > > PostGIS data - the challenge is just to map the information correctly).
> > > You
> > > can probably fully ignore the OSM runner, since the vector OSM
> > > fileformat
> > > has a pretty "weird" structure.
> > > 
> > > For learning more about the GeoDataDocument structure you can have a
> > > look
> > > at these this tutorial:
> > > 
> > > http://techbase.kde.org/Projects/Marble/Runners/DisplayGeoDataPlacemark
> > > 
> > > and these:
> > > 
> > > http://techbase.kde.org/Projects/Marble/Runners/Parse
> > > http://techbase.kde.org/Projects/Marble/Runners/LoadingOSM
> > > 
> > > So I suggest that you create a "postgis runner" plugin which would act
> > > as
> > > an interface between the PostGIS database and Marble's GeoDataDocument
> > > document model. Oh and yes of course this approach would allow for
> > > reversing the whole process. In the future you could allow users to edit
> > > polygons inside Marble and have the GeoDataPolygons get written back to
> > > the PostGIS database.
> > > 
> > > So if you look at the (relatively small) file parsing plugins you should
> > > see that this should all be doable. Additional incentive: If you
> > > implement this PostGIS runner and contribute it back to Marble then I
> > > owe
> > > you a beer and a pizza ;-)
> > > 
> > > Does that sound good to you? ;)
> > > 
> > > Best Regards,
> > > Torsten
> > > 
> > > 
> > > 
> > > 
> > > 
> > > 
> > > 
> > > -----Original-Nachricht-----
> > > Betreff: [Marble-devel] Using marble to render PostGIS data in different
> > > Projections Datum: Mon, 10 Feb 2014 11:45:05 +0100
> > > Von: Knut Krause <knut.krause at lagom.de>
> > > An: marble-devel at kde.org
> > > 
> > > Hi,
> > > 
> > > I have a PostGIS database with geometries. Now I'd like to do some
> > > computation on them. For my core algorithm I need the polygons in raster
> > > format. So I would be great if I could somehow use marble to draw my
> > > geometries on a flat surface like QImage. To show the result of my
> > > algorithm though I'd like to render a path on a plain marble widget.
> > > 
> > > Is it possible to use marble for that? Right now I use GDAL to transform
> > > the geometry from WKB to QPolygonF but that involeves a lot of number
> > > crunching myself to get the positions right and I fear I'm not smart
> > > enough to cope with projections correctly.
> > > 
> > > I thought something like
> > > 
> > > PostGIS -> <magic> -> GeoPainter -> QImage
> > > 
> > > would be great to render a set of geometries on an image as big as the
> > > bounding box of the geometries. Anyone here an idea if this works?
> > > 
> > > 
> > > Knut
> > > _______________________________________________
> > > Marble-devel mailing list
> > > Marble-devel at kde.org
> > > https://mail.kde.org/mailman/listinfo/marble-devel
> > 
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