j.vanknippenberg writes:
> Thanks for the input so far. :)
>
> I'll have a look at it, but if the person who prefers not to be famous
> :p can provide us with an example, it would be greatly appreciated ;)
OK, after much to-ing and fro-ing, I think we have
a solution in search of an explanation.
Because I grew up in a direct graphics world (in my day
the most exciting computer graphics was done with monospaced
fonts on huge line printers) I like to use a viewplane
coordinate system that goes from 0 to 1, or something
close to it. And I position my axes and data and whatnot
into that coordinate system with my NORMALIZE function,
which produces a two-element array for scaling and translating
data into this coordinate system.
In the SCATTER_SURFACE code we are talking about, I do this
to position the three axes:
xs = Normalize(xrange, Position=[-0.5,0.5])
ys = Normalize(yrange, Position=[-0.5,0.5])
zs = Normalize(zrange, Position=[-0.5,0.5])
; Scale the axes and place them in the coordinate space.
; Note that not all values in the Location keyword are
; used. (I've put really large values into the positions
; that are not being used to demonstate this.) For
; example, with the X axis only the Y and Z locations are used.
xAxis->SetProperty, Location=[9999.0, -0.5, -0.5], XCoord_Conv=xs
yAxis->SetProperty, Location=[-0.5, 9999.0, -0.5], YCoord_Conv=ys
zAxis->SetProperty, Location=[-0.5, 0.5, 9999.0], ZCoord_Conv=zs
Note the use of the [XYZ]COORD_CONV keywords. These are meant to
scale and translate (if I read the documentation correctly) the
object from it's native data coordinate system into MY coordinate
system.
So far, so good. The axes end up where they are suppose to be, etc.
But in the very next line, I also use the [XYZ]COORD_CONV keywords
to position the orbs (heads of the pins) and lines (shank of the pins)
in my data coordinate system:
FOR j=0,npts-1 DO BEGIN
(line[j]) -> SetProperty, XCoord_Conv=xs, $
YCoord_Conv=ys, ZCoord_Conv=zs
(orbs[j]) -> SetProperty, XCoord_Conv=xs, $
YCoord_Conv=ys, ZCoord_Conv=zs
ENDFOR
This appears to be the problem. When the range of the X, Y, and Z
axes are similar, the orb appears as I expect it to appear, as a
nice ball-like structure. But if, say, the X range is 100 times
larger than the Y and Z range, the orb turns into a flat disk.
I have learned in discussions this morning that I can avoid
this problem if I *don't* use the [XYZ]COORD_CONV keywords with
the orbs, but simply position them with the DATA keyword *while*
scaling and translating them. Huh!?
Here is the corrected code:
FOR j=0,npts-1 DO BEGIN
(line[j])-> SetProperty, XCoord_Conv=xs, $
YCoord_Conv=ys, ZCoord_Conv=zs
(line[j])->GetProperty, Data = Data
orbs[j]->SetProperty, Pos = [data[0, 1]*xs[1] + xs[0], $
data[1, 1]*ys[1] + ys[0], data[2, 1]*zs[1] + zs[0]]
ENDFOR
This appears to work for any axis data range. But *WHY* it
works is a complete mystery to me. I'd be interested in
hearing any good theories. :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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