[Qgis-developer] [Qgis-user] Using/visualizing 3D data (Z values)

[Vincent Picavet]

Hi all,

Le mardi 25 septembre 2012 15:47:14, Etienne Tourigny a écrit :
> reviving this old thread because I'm interested in using the z-value
> (elevation) from kml files (type wkbMultiLineString25D) in a qgis plugin.
> 
> Are there any plans to introduce z-value (25D) support in 2.0?

We at Oslandia are working on 3D processing in databases and visualization.

We have an early piece of code opening a 3D vector layer in QGIS and feeding 
it to QGIS Globe. This works with real 3D objects loaded from database, and 
should work with 2.5D (x, y, z) shapefiles too theoritically.

We have to get it in a better shape before starting to provide pull requests 
on this, but you should see this coming in a couple of months.

Then this will open a whole new range of needs with 3D data, but one step 
after the other...

Vincent


> 
> Experimenting has shown that doing geom.exportToWkt() strips the z-value.
> 
> How can I currently handle z-values? I understand that I would have to
> parse the wkb directly, is this possible in python? If so can someone give
> me some pointers?
> 
> Other option - external python library like shapely? It seems shapely does
> support z levels.
> 
> Or would it be simpler to parse the kml files by hand using an xml parser,
> as syntax is relatively simple?
> 
> 
> regards,
> Etienne
> 
> On Mon, Dec 5, 2011 at 8:02 AM, Marco Hugentobler <
> 
> marco.hugentobler at sourcepole.ch> wrote:
> > Hi Paul
> > 
> > Unfortunately, the current geometry system does not handle z- and
> > m-values in a sound way.
> > Some tools consider z and others don't. M-values are even more difficult
> > as they cannot be accessed by the QGIS API (z-coordinates can be read by
> > parsing the binary format of the geometry).
> > 
> > An overhaul of the geometry system is planned for version 2.
> > 
> > Regards,
> > Marco
> > 
> > On 05.12.2011 10:42, Paul Lens wrote:
> > > Hi all,
> > > 
> > > 1. I made a TIN surface, using the interpolation plugin, from a point
> > > shapefile (with "ALTITUDE" field) and  3D line shapefiles. I lost time
> > > trying to extract the relevant lines from the line shapefiles without
> > > loosing the 3D information (Z values of the nodes).
> > > If I remember well, I first used "Merge Layers" from the mmqgis
> > > plugin, and it kept the Z information. Than, I used the Intersection
> > > command in the Vector menu, and the Z information was lost. Finally,
> > > after manually selecting the relevant lines and using "save as", I got
> > > the expected 3D line shapefile keeping the Z values.
> > > Is this loss of Z information a known limitation of the gdal vector
> > > commands in QGIS (vector menu) and is this limitation affecting all
> > > these commands? Or did I do something wrong?
> > > 
> > > 2. In a second step, I wanted to be able to easily see (through
> > > labeling a Z field) or ask (with the identify command) those Z values
> > > from the 3D lines, so as to fine tune the interpretation of the
> > > topography.
> > > Again the gdal tool (in Vector menu) "Node Extraction" lost all Z
> > > information.
> > > Is there a workaround to create a point shapefile with a Z field? Or,
> > > at least, to keep the Z values in a point shapefile, rasterize it so
> > > as to be able to visualize the Z value using  the "Identify" command
> > > on the raster?
> > > 
> > > Thanking all the developers for this wonderful program,
> > 
> > --
> > Dr. Marco Hugentobler
> > Sourcepole -  Linux&  Open Source Solutions
> > Churerstrasse 22, CH-8808 Pfäffikon SZ,
> > Switzerlandmarco.hugentobler at sourcepole.ch http://www.sourcepole.ch
> > Technical Advisor QGIS Project Steering Committee
> > 
> > 
> > 
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