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

[Etienne Tourigny]

Hi all

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?

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
>
>
>
> _______________________________________________
> Qgis-user mailing list
> Qgis-user at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/qgis-user
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-developer/attachments/20120925/4a326999/attachment-0001.html>