More GriddedNDSet Questions

[Bill Hibbard]

 Hi Ken,

I've thought about it and cannot explain the exact events
you are seeing. But in general I can say that when you see
pixels as squares centered on sample locations, your data
are being rendered using texture mapping (you can disble
this via GraphicsModeControl). When you see pixels as
pairs of triangles, you are not seeing texture mapping.

The main thing that confuses me is that with a GriddedSet
you should see a curved texture map and should not see
triangles. If you set a transparency (i.e., alpha) value that
might disable texture mapping for the GriddedSet, but not
for the LinearSet (which uses non-curved texture mapping).

That's all I can think of.

Good luck,
Bill

  ----- Original Message -----
  From: "Kenneth Evans"
  To: Visad
  Subject: More GriddedNDSet Questions
  Date: Fri, 6 Apr 2007 11:29:48 -0500

  Hi,

  I guess I still don’t understand GriddedNDSets.  What I am trying to
  do this time is the following:

  I have a 2D array of intensity data as found, for example in an
  image.  If I plot that as (x, y) -> Intensity using a Linear2DSet:

  Linear2DSet( xMin, xMax, nX, yMin, yMax, nY)

  Then I get a plot with the pixels showing as squares.  The squares
  are centered at the values in the set and extend past the axes.

  If I do the same thing, using a Gridded2DSet:

  Gridded2DDoubleSet(domainType, new double[][] {xVals[0], yVals[0]},
  nX, nY);

  where xVals[0] is {xMin, 
, xMax, Xmin,
} etc. (that is, they are
  intended to be the same values as used in the Linear2DSet), then the
  squares get turned into triangles, and nothing extends beyond the
  axes.  The two plots don’t “look” the same.  Apart from the
  overextending, the second appears washed out.

  In general, I want to do coordinate transformations, so the xVals and
  yVals will be arbitrary.  In that case there will be distortion of
  the pixels, and I can see that interpolation of some sort is
  necessary.  It just seems that two results should look the same as
  long as there is no distortion.

  Am I doing something wrong or is this just the way it is?

  -Ken
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