Thanks for the advice on using Slab. That gets me a couple of steps closer
to my goal. I have now run into another difficulty. I want to Construct a
field corresponding to the TIFF image, but with actual (x,y) positions, then
attach the image colors to this field. My reason for doing this is so that
I then hope to use Map to map these colors onto the rubbersheeted image of
the field with the elevation data. To use Map I believe I need the two
fields to be in the same coordinate system.
They must overlap at least by some amount or you get a field of
invalid positions from Map, so yes, the coordinates must be similar.
You are going to have a great deal of trouble mapping a 2D surface
onto a 2.5D rubbersheet though so don't even try. (2.5D means a 2D
surface projected into 3-space, i.e., the positions are 3D but the
topology is 2D). Map will refuse to do it, period, but even if it
didn't refuse, the only places where the two fields touched would be
where the 2D plane intersected the 2.5D object, so you'd get spotty
coverage.
I have been doing some testing with Construct and Map to see how to map
colors, without much success.
Um, that's why the gods invented Colormap. (:-)
Yes, you can do the same with Map but it's more trouble than it's
worth usually.
My simple test has two Constructed fields
which are identically created.
Good so far
I pass each through Autocolor (here I vary
the parameters)
why? just map the data from one to the other then Colormap... but
keep reading...
then use Map with Positions and Colors, i.e. I try to map
the colors of one field onto the other.
Colors are RGB 3-vectors (usually, esp. if you used AutoColor and
didn't set the "delayed" flag). Map ALWAYS interpolates (even if it
doesn't have to). Interpolated RGB 3-vectors are usually not very
good looking, since RGB is a very non-linear space (after
transformation back to the visual representation we know and love).
In other words, you can't move from point A to point B in RGB space
in a straight line and expect the colors along the line to be
"smooth" visually. So abandon this approach.
This gives an error message about
unsupported color format. If I send the output of each Autocolor module to
Image it displays OK. Am I trying to do something with Map that it was not
designed to do?
Almost certainly, you created scalar data back in Construct so you'd
have something to Autocolor.
Now you've asked Map to do the following:
For each position in the input field, look up in the map field's
positions to find a match. Interpolate the map field positions as
necessary to get an exact match. Interpolate the map data
corresponding to the map positions that were used, to get an
interpolated data value that corresponds to the interpolated map
position. Carry that value back to input and stuff it into the
designated component, indexed to the original position we were
working on.
OK, you said: "look up by positions, retrieve data (which is scalar),
stuff into colors of input, then render."
Renderer says: "barf! colors cannot be scalar integers (or whatever
you tried to feed me)."
(ok, it said "unsupported color format" but I like my error message
better; it has more snap.)
So let's roll way back up to where you said you had two identical
fields. Why not just Replace the colors from the source field onto
the destination field? They have the same exact positions and number
of colors and everything lines up beautifully and Replace does NO
interpolation, so you don't even get weird round-off errors or wacky
RGB values, and it happens instantaneously since it's just a pointer
copy operation under the covers. Map involves some heavy-duty number
crunching. Big nasty Maps can take considerable time to chew on the
problem. Map is NOT smart enough to recognize that the positions are
perfectly aligned. It will still do all the math. And due to possible
round-off error, it may not even come up with the same answer.
Same for your TIFF: construct a "blank field" with the right number
of positions and connections (delta 1 in both dimensions, since it's
a pixel map), then in one instantaneous sleight of hand, lift the
colors of the TIFF and drop onto this field.
NOW rubbersheet (after Marking the elevation data), or just directly
Compute new positions based on X, Y, elevation, and any scaling
factors you want to apply to X,Y, Z. You map a 2D surface to a 2D
surface, THEN you make it 2.5D. Much simpler.
Or, go all the way back to what Greg said. An image in DX is just a
2D field of positions and connections (quads) with colors (no data).
You should be able to Replace the elevation data (from wherever it
comes), or calculate it in some interesting way (for example, Convert
colors to HSV, then elevate the "saturation") onto the "image" field
then rubbersheet or Compute positions. The original colors stay
firmly attached to the transformed positions so you don't need to do
any mapping or colormapping or interpolation of colors.
Chris Pelkie
Vice President/Scientific Visualization Producer
Conceptual Reality Presentations, Inc.
30 West Meadow Drive
Ithaca, NY 14850
[EMAIL PROTECTED]
