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, Switzerland
[email protected] http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee
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