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Re: IDLgrPoly[line|gon] and cv_coord [message #33561 is a reply to message #33483]

Wed, 08 January 2003 13:04

Rick Towler
Messages: 821
Registered: August 1998

Senior Member

"David Fanning" <david@dfanning.com> wrote:
> Rick Towler (rtowler@u.washington.edu) writes:
>
>> I think you should be careful how you are phrasing this. Object
graphics
>> uses a right-handed rectangular coordinate system. The units and view
>> volume may be arbitrary but you always have a point [0,0,0] and 3
mutually
>> perpendicular axes with regular intervals passing thru it which define
>> [x,y,z] values.
>
> Humm. I wonder? While it's true that I have never
> used anything *but* a rectangular coordinate system
> for a program, it is not immediately obvious to me
> that this is the only possible coordinate system that
> can be set up. I'm almost certain a (0,0,0) point is
> not required. What makes you think this is the case?

I can't argue that there doesn't exist a graphics library whose coordinate
system is not rectangular, but openGL's is. Try defining an IDLgrPolygon
with [angle, radius, z] values instead of [x,y,z]. I don't think you'll get
what you were expecting.

I didn't mean to imply that you need [0,0,0] in your view. What I meant was
that whether you choose to include [0,0,0] in your view volume or not the
origin is out there, somewhere. You can ignore this until you start
rotating things. Models are rotated about a defined axis which passes
through [0,0,0] regardless of your view settings.

-Rick

Exhibit A:

orb=obj_new('orb', pos=[20,0,0], radius=0.5, style=1, density=0.5)

oview=obj_new('idlgrview', viewplane_rect=[19,-1,2,2], eye=3, $
zclip=[1,-1])

oview -> add, orb

owin = obj_new('idlgrwindow')

owin -> draw, oview

for n=0,500 do begin
orb->rotate,[0,0,1], 0.01
owin -> draw, oview
endfor

orb -> reset
orb -> setproperty, pos=[0,0,0], color=[100,200,100]
oview -> setproperty, viewplane_rect=[-1,-1,2,2]

for n=0,500 do begin
orb->rotate,[0,0,1], 0.01
owin -> draw, oview
endfor

obj_destroy, [oview, owin]

end

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[Message index]

		Re: IDLgrPoly[line\|gon] and cv_coord By: David Fanning on Wed, 08 January 2003 10:37
		Re: IDLgrPoly[line\|gon] and cv_coord By: Rick Towler on Wed, 08 January 2003 09:55
		Re: IDLgrPoly[line\|gon] and cv_coord By: paul wisehart on Wed, 08 January 2003 05:58
		Re: IDLgrPoly[line\|gon] and cv_coord By: David Fanning on Wed, 08 January 2003 05:23
		Re: IDLgrPoly[line\|gon] and cv_coord By: Thomas Gutzler on Tue, 07 January 2003 23:16
		Re: IDLgrPoly[line\|gon] and cv_coord By: Rick Towler on Tue, 07 January 2003 15:15
		Re: IDLgrPoly[line\|gon] and cv_coord By: David Fanning on Tue, 07 January 2003 14:58
		Re: IDLgrPoly[line\|gon] and cv_coord By: Rick Towler on Wed, 08 January 2003 13:04

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		Re: IDLgrPoly[line\|gon] and cv_coord By: David Fanning on Wed, 08 January 2003 10:37
		Re: IDLgrPoly[line\|gon] and cv_coord By: Rick Towler on Wed, 08 January 2003 09:55
		Re: IDLgrPoly[line\|gon] and cv_coord By: paul wisehart on Wed, 08 January 2003 05:58
		Re: IDLgrPoly[line\|gon] and cv_coord By: David Fanning on Wed, 08 January 2003 05:23
		Re: IDLgrPoly[line\|gon] and cv_coord By: Thomas Gutzler on Tue, 07 January 2003 23:16
		Re: IDLgrPoly[line\|gon] and cv_coord By: Rick Towler on Tue, 07 January 2003 15:15
		Re: IDLgrPoly[line\|gon] and cv_coord By: David Fanning on Tue, 07 January 2003 14:58
		Re: IDLgrPoly[line\|gon] and cv_coord By: Rick Towler on Wed, 08 January 2003 13:04