IDL Experts,
I have been busting my head over this one for some time now. I have
been getting help from RSI tech support (BIG thanks to Jim Howell! - I
know your busy) but I thought I'd throw it out here and see if anyone
has solved it before ?
I will pose the question with a simple example. I volume render a 3-D
cube, with dimensions [20,20,20]. I draw a line from the origin to a
point P (xc,yc,zc). I then create a cutting plane through the cube
perpendicular to the line. I then want to draw a local xy coord
system on the cutting plane centered at the point P. The problem arises
when the dimensions of the cube are not equal which effectively sets
!x.s, !y.s and !z.s to be different. It seems that the transformation
angles used do NOT reflect this change properly (IDL stretching th
Z-axis filling the screen) yet the cutting plane normal (which is used
to define the transformation angles) IS dependent on the scaling in each
direction:
I have included a sample program showing a X (blue) and Y (Green) local
axis on the cutting plane. When DataDim = [20,20,20] everything looks
fine. Try setting
DataDim[20,20,10] - The blue Xaxis cuts through the volume indicting it
does not lie parallel to the plane.
If anyone has any ideas , I would appreciate any help. I have some
experience with Transformation matrices from my robotic/kinematic
background but a am an IDL newbie!
Thanks in Advance
Richard Tyc
Project Engineer
St. Boniface Hospital Research Center
richt@sbrc.umanitoba.ca
Here's some snippet of code illustrating the problem (note i have left
some code out to simplify - see example attached):
DataDim = [20,20,20]
xfac = 0.5 & yfac = 0.5 & zfac = 0.4
; define Point P
xc = xfac*DataDim[0] & yc = yfac*DataDim[1] & zc = zfac*DataDim[2]
; create data representing cube - it will become cube[20,20,20] array
cube = CubeData(DataDim[0],DataDim[1],DataDim[2])
s=size(cube) & xs=s[1]-1 & ys=s[2]-1 & zs=s[3]-1
;create cutting plane
LenVox = sqrt((xc*xs/DataDim[0])^2 + (yc*ys/DataDim[1])^2 + $
(zc*zs/DataDim[2])^2)
cutplnVox = [(xc*xs/DataDim[0])/LenVox, (yc*ys/DataDim[1])/LenVox, $
(zc*zs/DataDim[2])/LenVox, -LenVox ]
cpNorm = cutplnVox[0:2] ; normal vector for line from origin to P
; normalized distance to point P
cpNormCtr = [xc/s[1],yc/s[2],zc/s[3]]
; setup scaling
Scale3, XRange=[0,xs], YRange=[0,ys], ZRange=[0,zs]
................
................
; create volume
oVolCube = OBJ_NEW('IDLgrVolume', cube, $
xcoord_conv=!x.s,ycoord_conv=!y.s, zcoord_conv=!z.s )
oVolCube->setproperty,cutting_planes=[cutplnVox]
oVolCube->setproperty,/zbuffer
oCannula = OBJ_NEW('IDLgrPolyLine', color=[0,255,0], $
[[0,0,0],[cpNormCtr]], thick=5)
; create local coord frame axis this will be transformed
oXCaxis = OBJ_NEW('IDLgrAxis',0,color=[0,0,255],range=[0,CanAxLen], $
major=0,minor=0,xcoord_conv=!x.s,ycoord_conv=!y.s, $
zcoord_conv=!z.s,/notext)
oYCaxis = OBJ_NEW('IDLgrAxis',1,color=[0,255,0],range=[0,CanAxLen], $
major=0,minor=0,xcoord_conv=!x.s,ycoord_conv=!y.s, $
zcoord_conv=!z.s,/notext)
oModel->Add,oVolCube
oModel->Add,oCannula
oModelC->Add,oXCaxis
oModelC->Add,oYCaxis
; reset global view (cube data) to fit and display
t3d,/reset
t3d,trans=[-.5,-.5,-.5],scale=[.577,.577,.577]
t3d,rot=[-90, 300, 0]
t3d,rot=[ 220, 0, 0 ]
t3d,trans=[ .5, .5, .5]
oModel->SetProperty,transform=!p.t ;set for cube here only
; Now setup transformation to bring local coord system
; out to Point P This is where the heart of the problem is I think !
Rxy = sqrt(cpNorm[0]^2 + cpNorm[1]^2 )
if ((cpNorm[0] eq 0.0) and (cpNorm[1] eq 0.0)) then Az = 0.0 $
else Az = ATAN(cpNorm[1], cpNorm[0]) * !radeg
if ((Rxy eq 0.0) and (cpNorm[2] eq 0.0)) then Ay = 0.0 $
else Ay = ATAN(cpNorm[2], Rxy) * !radeg
t3d,/reset,rot=[0,90-Ay,Az]
t3d,trans=[cpNormctr[0],cpNormctr[1], cpNormctr[2]]
ctrans = !p.t
; reformat image view area same as above for cube data
t3d, /reset, trans=[-0.5,-0.5,-0.5],scale=[.577,.577,.577]
!p.t = ctrans # !p.t ;reflect previous transformation
t3d,rot=[-90,300,0]
t3d,rot=[220,0,0]
t3d,trans=[.5,.5,.5]
oModelC->SetProperty,transform=!p.t
.... and draw data
-
Attachment: richt.vcf
(Size: 0.29KB, Downloaded 68 times)
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