[Paraview] Scalar draped topography distortion

[Eric E. Monson]

Hello Cecilia,

I have done a small bit of texture mapping in ParaView, but not on distorted surfaces, and it sounds like you are dealing with a subtle issue that I've never run across.

You will have much more luck joining the ParaView mailing list and posting your questions there. When you post issues to the list they are exposed to so many more people with a wide range of experience. You can sign up at: http://www.paraview.org/mailman/listinfo/paraview

I am also CCing the list, so hopefully someone will have tried something similar.

Good luck,
-Eric

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Eric E Monson
Duke Visualization Technology Group

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On Jun 20, 2011, at 6:38 PM, Cecilia Del Pardo wrote:

Hello Eric,

I have been looking on the Internet for ways to obtain a scalar-draped topography in Paraview but so far I have not been able to obtain it.  In the many pages I looked, I found that you answered a lot of questions regarding the use of ParaView. I would like to know if you would be able to provide some help with my problem.
We have been able to successfully convert stacks of grd scalar files to vtk format to make a 3d volume (through the procedure described below), and have also successfully converted single grd (topography) files to vtk format.   We have plotted both of these types of files in Paraview successfully, however what we would really like to do is drape a scalar grid (i.e. surface stress) on top of a topography grid in Paraview – this is where we are having problems.  
 
To convert our stress grid files (.grd files) to a VTK format we use a script obtained from Thorston Becker (http://geodynamics.usc.edu/~becker /software/grd2vtk_README)
We use the grd2vtk_cart script, which assumes that the .grd files are Cartesian and creates a rectilinear vtk grid.   An example of this is attached (model_PVplot.pdf ).

To generate the stress-draped topography view in Paraview, we first convert a topography .grd file to a vtk file using the same procedure above.   This file is displayed accurately in ParaView (using the first 4 steps below), however when we try to drape an “image” over the topography (i.e., the surface layer of our stress grids), we encounter some distortion problems.    We use the following steps, which we picked up from a handful of comments from other people online:
1.    Load topo .vtk file in ParaView
2.    Filters→ Clean to Grid
3.    Filters → Extract to Surface
4.    Filters → Warp by Scalar
5.    Filters → Texture Map to Plane
6.&n bsp;   (outside of Paraview) Create drape image – make a gmt postscript file of scalar surface (stress map), convert this to a jpg, apply a 90 deg. clockwise rotation and a vertical axis flip (photoshop)
7.    (back in Paraview) Display panel: Apply Texture → select stress map jpg

Using these rather archaic steps, we do end up with a scalar-draped topography scene, but the draped file is slightly distorted – it almost looks like a projection issue, where the scalar map is shifted a few km to the NE and the issue gets larger along the southern portions of the scene.   To make sure the projection issue wasn’t creeping in when we made our scalar map in GMT, we generated a map with a simple linear projection (using –Jx option).  This did not help.

I would like to know if it is possible for you to give me some advice for how to treat the scalar-draped topography issue.   Have you done this, and if so, do you have an alternative method? 

Thank you,

Cecilia

Cecilia Del Pardo
Geophysics Ph. D. Candidate
Research Assistant 
Geological Sciences Department
University of Texas at El Paso
El Paso, TX 79968
cdelpardo at miners.utep.edu




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