Re: [opendx-users] 3D triangular mesh plotting problem

[Chris Pelkie]

All DX arrays are indexed from 0. I suspect you are off by one in your connections so you are seeing really stretched triangles (the stripes). This is suggested by the fact that your first and only triangle (below) starts with 1. If it's a pain to change prior to DX, you can Mark("connections"), Compute(a-1), Unmark to fix them prior to rendering.

Connections normally requires the attribute "ref" "positions" though maybe DX fills in the blanks if you don't provide it explicitly.

Rubbersheet would assume a 2D positions and scalar data to be used as Z. You don't want that as you already have Z in the positions. So you can just put your scalar data into "data", then Color/Colormap, etc. (and be aware of the "constantarray" object type: more compact in this case below, though not useful for your upcoming 'interesting' scalar data).

<x-tad-bigger>____________________________
Chris Pelkie
Vice President (607) 257-8335
Conceptual Reality Presentations, Inc.
30 West Meadow Drive
Ithaca, NY 14850

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On Jul 4, 2005, at 0:54, Bill Haneberg wrote:

I've looked through the archives and haven't found anything quite like the problem I've encountered, so I'm hoping that someone on the list might have a suggestion.

I am trying to plot a triangulated irregular network (TIN) representing the face of a rock outcrop. My approach has been to write a dx file defining a large number of triangles (all but the first values of each object omitted for brevity):

<x-tad-bigger>object 1 class array type float rank 1 shape 3 items 29406 data follows
1023.64400000000 5977.67500000000 22.3090000000000
< 29405 values omitted>
object 2 class array type int rank 1 shape 3 items 58785 data follows
1 12169 8620
< 58754 values omitted>
attribute "element type" string "triangles"
object 3 class array type float rank 0 items 29406 data follows
1.0
< 29405 values omitted>
attribute "dep" string "connections"
object "irregular positions irregular connections" class field
component "positions" value 1
component "connections" value 2
component "data" value 3

</x-tad-bigger>In the simplest case, I import the dx file and display the TIN using Import -> Color -> Shade -> Image. The problem is that the sloping irregular outcrop surface is bisected by a striped plane roughly parallel to the two long dimensions and perpendicular to the short dimension. There is also a large triangular artifact near the top of the outcrop. I know the triangulation is ok because the TIN plots without any problems in R and Mathematica. So, the problem is between me and OpenDX, not the TIN. I've put images of both the correctly rendered TIN and the problematic OpenDX version at this URL:

http://www.haneberg.com/tin.html

for anyone who would like to take a look.

I realize that I could Rubbersheet a collection of 2D triangles if my only objective were to display the surface. I eventually want to change the data values from the constant 1.0 to values that convey a scalar value for each triangle. I don't think that will work with Rubbersheet. Or, can I have one data component linked to the positions and a second data component linked to the connections?

Please let me know if you have any suggestions.

Thanks,

Bill
--------------------------------------
William C. Haneberg, Ph.D.
Consulting Geologist
www.haneberg.com
(206) 935-0846