[Qgis-user] TIN Interpolation

[Marco Hugentobler]

Hi Bernd

 >So, how are line features supposed to work in interpolation plugin? Or 
how can i give structure lines hight values that make sense?

Well, somehow you need to say the plugin what the values to interpolate 
are. Currently possible is to take from attribute or from z-value (for 
2.5D geometry types). Where do you have the height values in your data?

 >So, how are line features supposed to work in interpolation plugin?

The line features are used to modify the triangulation. The 
triangulation is modified such that no edge crosses a breakline or 
structure line (constrained Delaunay triangulation). The difference 
between handling of breaklines and structure lines is that cubic 
interpolation produces a sharp break rather than a continuous one.

Please note that the interpolation plugin has some numerical problems in 
the TIN creation that may lead to crashes (especially for data in 
degrees). There is the option to dump the generated triangle net, so you 
can see what the plugin does.

Regards,
Marco

On 23.07.2013 23:44, Bernd Vogelgesang wrote:
> Hi folks,
>
> i'm currently playing around with a set of LIDAR points (200m Grid, 
> but for free).
> Trying to "pimp" the model up, i also added some hight points from a 
> topo-wms and wanted to add break lines and structure lines (streams).
>
> Now i'm a bit clueless about the usage of the line features. The 
> interpolation plugin always asks for a interpolation attribute, which 
> doesn't make much sense cause those lines don't have them. They choice 
> of the attribute field seems automatically limited to numerical fields 
> (which makes sense for the z-values of points).
>
> When i just create and pick a numerical field without values, the 
> lines seem not to have any effect on the interpolation. When i use e.g 
> the id, it has bizarre effects on the outcome.
>
> So, how are line features supposed to work in interpolation plugin? Or 
> how can i give structure lines hight values that make sense?
>
> All tutorials and documentations (e.g. 
> http://docs.qgis.org/1.8/html/en/docs/user_manual/plugins/plugins_interpolation.html 
> ) i found on that only cover the unproblematic usage of points and 
> leave out the lines completely.
>
> Thanx
> Bernd
>


-- 
Dr. Marco Hugentobler
Sourcepole -  Linux & Open Source Solutions
Weberstrasse 5, CH-8004 Zürich, Switzerland
marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee