[Paraview] Offset between grid and points on spherical projection

[Moreland, Kenneth]

This looks like it might be caused by the coincident topology resolution feature in ParaView's rendering. The problem when trying to draw surfaces and points or lines on that surface as you are doing is that you get z-buffer fighting so that the points/lines don't just show up on top like you want.

ParaView implements a couple of tricks to prevent this from happening, but they all sometimes cause shifts in the data so that they do not line up correctly. My suggestion is to first turn off coincident topology resolution and see if that fixes this problem (although it might introduce a new one). Go to settings and then Render View -> General to get to the coincident topology resolution options.

-Ken

From: Fernando Paolo <fspaolo at gmail.com<mailto:fspaolo at gmail.com>>
Date: Thursday, June 26, 2014 1:36 PM
To: "paraview at paraview.org<mailto:paraview at paraview.org>" <paraview at paraview.org<mailto:paraview at paraview.org>>
Subject: [EXTERNAL] [Paraview] Offset between grid and points on spherical projection

Hello,

I have a 2d grid projected on top of a spherical surface. On the same surface, and on top of the grid, I am also projecting a set of points delimiting the boundaries of the quantity in question. The problem is that both the grid and the points when plotted together are displayed with an offset in between them (in the "r" direction from the spherical projection). Also interesting is the fact that when I change the angle of view the "offset" also changes (see attached figures).

The coordinates of both the grid and the points are simply converted from spherical lon/lat/radius=1 to cartesian xyz.

The points are projected using an UNSTRUCTURED GRID format (polydata ascii file). And the grid is projected using the XDMF 3DSMesh, with the following template:

   <Grid Name="Mesh" GridType="Uniform">
     <Time Value="%f" />
     <Topology TopologyType="3DSMesh" NumberOfElements="{0} {1} {2}"/>
     <Geometry GeometryType="XYZ">
       <DataItem Name="Coordinates" Dimensions="{3} {4}" NumberType="Float" Precision="4" Format="HDF">
         PATH_TO_XYZ
       </DataItem>
     </Geometry>

     <Attribute Name="DATA_NAME" AttributeType="Scalar" Center="Cell">
       <DataItem Dimensions="{5} {6} {7}" NumberType="Float" Precision="4" Format="HDF">
         PATH_TO_DATA
       </DataItem>
     </Attribute>
   </Grid>

If both datasets have a radius = 1, why is there any offset in between them? Since this offset also changes with the angle of view, it seems that both datasets are not being projected on top of the same spherical surface (note: I've tried setting different radius for both datasets). How can I fix this?

I appreciate any help!
-fernando


[Inline image 1]

[Inline image 2]


--
Fernando Paolo
Institute of Geophysics & Planetary Physics
Scripps Institution of Oceanography
University of California, San Diego

web: fspaolo.net<http://fspaolo.net>
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