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

[Knut Krause]

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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