Rob wrote:
> Hi,
>
> I'm trying to texture map an image onto a cylindrical section (created
> with an IDLgrPolygon object) but I'm having trouble determining the
> proper texture mapping coordinates to display it properly. Can I use
> the vertices or connectivity arrays that were calculated from MESH_OBJ
> somehow for this?
Yes, something as simple as this will work:
zMax = MAX(verts[2,*], MIN = zMin)
yMax = MAX(verts[1,*], MIN = yMin)
texCoords = [(verts[2,*] - zMin) / (zMax - zMin), $
(verts[1,*] - yMin) / (yMax - yMin)]
You'll have to pick the plane you want to project your image onto. In
the case above I chose the zy plane. This may or may not be right for
you, I didn't really look.
Now, maybe you already know how to do this and you realize that this
won't apply the texture uniformly across the cylinder and that's why you
are posting...
To do that I would create your cylinder orthoginal to the XZ plane
centered about the origin (you can worry about transforming it later).
Then I would calculate the "horizontal" texcoords as a function of the
angle of rotation about the Y axis:
yMax = MAX(verts[1,*], MIN = yMin)
rotAngle = atan(verts[0,*],verts[2,*]) * !RADEG
cMax = MAX(rotAngle, MIN = cMin)
texCoords = [(rotAngle - cMin) / (cMax - cMin), $
(verts[1,*] - yMin) / (yMax - yMin)]
You'll probably have to dress that up a bit.
So here it is all together. Enjoy!
-Rick
pro cylindrical_sector
; This procedure attempts to create a section of a cylindrical
; shell.
; Use extrusion to create the cylindrical section
; First create an arc in the x-y plane
radius = 1.0 & height = 1.0
th_lo = 25.0 & th_hi = 180.-th_lo
n = 50 & dth = (th_hi-th_lo)/(n - 1.0)
th = th_lo+dth*findgen(n)
x = radius * cos(!dtor * th)
z = radius * sin(!dtor * th)
y = replicate(-0.5*height,n)
type = 5 ; extrusion
; Create the array based on x and y
array = fltarr(3,n)
for i = 0,n-1 do array[0:2,i] = [x[i],y[i],z[i]]
; Use MESH_OBJ to create the extruded section
mesh_obj, type, verts, polys, array, p1=1, p2=[0,1,0]
; Create a model into which we'll stuff the POLYGON object
omodel = obj_new('IDLgrModel')
; Create the image data to be texture-mapped onto the
; POLYGON object.
;image_data = bytscl(hanning(32,32))
image_data =
read_image(filepath('glowing_gas.jpg',subdir=['examples','da ta']))
help, image_data
oimage = obj_new('IDLgrImage',image_data)
; Create the POLYGON object
osection = obj_new('IDLgrPolygon',verts,style = 2,polygons = polys, $
color = [255,255,255],texture_map = oimage)
omodel->add,osection
; easy method - not quite right
xMax = MAX(verts[0,*], MIN = xMin)
yMax = MAX(verts[1,*], MIN = yMin)
texCoords = [(verts[0,*] - xMin) / (xMax - xMin), $
(verts[1,*] - yMin) / (yMax - yMin)]
osection -> SetProperty, texture_coord=texCoords
xobjview,omodel, /block
; better method
yMax = MAX(verts[1,*], MIN = yMin)
rotAngle = atan(verts[0,*],verts[2,*]) * !RADEG
cMax = MAX(rotAngle, MIN = cMin)
texCoords = [(rotAngle - cMin) / (cMax - cMin), $
(verts[1,*] - yMin) / (yMax - yMin)]
osection -> SetProperty, texture_coord=texCoords
xobjview,omodel, /block
obj_destroy, [omodel,oimage]
end
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