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Re: 3d device coordinates from a 3D polyline.... [message #81553 is a reply to message #81518]

Thu, 04 October 2012 09:23

George.millward
Messages: 26
Registered: October 2012

Junior Member

On Wednesday, October 3, 2012 2:29:02 PM UTC-6, Karl wrote:
> On Tuesday, October 2, 2012 3:32:02 PM UTC-6, Mike Galloy wrote:
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>> On 10/2/12 3:02 PM, Karl wrote:
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>>> It should also be possible to write a general-purpose function that
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>>> takes a "leaf" graphics object and walks up the scene graph,
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>>> computing the single 4x4 combined matrix and returns it. You would
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>>> then use that single matrix to transform your points.
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>>>
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>>> In a way, you are duplicating the entire transform that IDL applies
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>>> to the points via the underlying graphics system (OpenGL). I don't
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>>> remember if there is a way to get this transform directly from IDL -
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>>> don't think so. And someone out there may have already written an
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>>> IDL function to do this. But, I don't know of any.
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>> Isn't this the ::getCTM() method or am I misunderstanding the situation?
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>> Mike
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>> --
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>> Michael Galloy
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>> www.michaelgalloy.com
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>> Modern IDL: A Guide to IDL Programming (http://modernidl.idldev.com)
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>> Research Mathematician
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>> Tech-X Corporation
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> yep, that's it.

Actually, this IS a 3D perspective view I'm working with. I have a polyline in a 3D perspective scene. One end of the polyline is at the center of my 3D coordinate system (ie, [0,0,0]) and the other end is at (say) [+10,0,0]. As I rotate it around with a trackball the 2D projection in the window can assume any
'size' (from a single pixel dot to a line of length 10) and any orientation (0 to 360 if you like).

I'm amazed there isn't an inbuilt function to tell me what these 2D window coordinates are - but there you go, nothing like spending a couple of weeks fiddling with IDL - it's fun right ?

I'll take a look a Michael's object graphics chapter. For me that is the ideal sample chapter....

Cheers

George.

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[Message index]

		3d device coordinates from a 3D polyline.... By: George.millward on Fri, 28 September 2012 14:30
		Re: 3d device coordinates from a 3D polyline.... By: George.millward on Thu, 04 October 2012 09:23
		Re: 3d device coordinates from a 3D polyline.... By: Karl[1] on Thu, 04 October 2012 13:16
		Re: 3d device coordinates from a 3D polyline.... By: Karl[1] on Wed, 03 October 2012 13:29
		Re: 3d device coordinates from a 3D polyline.... By: Michael Galloy on Wed, 03 October 2012 07:49
		Re: 3d device coordinates from a 3D polyline.... By: Michael Galloy on Tue, 02 October 2012 14:32
		Re: 3d device coordinates from a 3D polyline.... By: Karl[1] on Tue, 02 October 2012 14:02
		Re: 3d device coordinates from a 3D polyline.... By: George.millward on Tue, 02 October 2012 09:46
		Re: 3d device coordinates from a 3D polyline.... By: George.millward on Thu, 04 October 2012 13:21

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