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Poser - OFFICIAL F.A.Q (Last Updated: 2024 Dec 23 1:20 pm)



Subject: Writing Mac version of MTMirror -- Do all .OBJs have origin in object center?


duanemoody ( ) posted Mon, 06 November 2000 at 4:18 PM ยท edited Mon, 23 December 2024 at 11:21 AM

After Masa confirmed my guess on how his program works, I examined the raw .OBJ data for the heads of P4Male, P4Female and Vicky. I noticed right off that they all have a center line rather than a central strip of polygons. I also noticed that the center line always rests on the X-axis' zero point, making corresponding left-right points have the same X value (except that one's negative and the other positive). Awfully convenient for writing a program, rather than having to calculate offsets. Before I dive in headfirst, I'm wondering if this was Zygote's preference when they built these three models, or if it's a given with .OBJ that the object's center defines the origin for the XYZ coordinates? If anyone knows I'd be grateful.


JeffH ( ) posted Mon, 06 November 2000 at 4:32 PM

Attached Link: http://www.renderosity.com/messages.ez?ForumID=12355

Ask these questions in the Developer Forum section as well: http://www.renderosity.com/messages.ez?ForumID=12355 Zygote built one half of the figure OBJ then mirrored it to get the other half. Many modeling programs have this feature, but not all OBJ files are built this way. -JH.


Mason ( ) posted Tue, 07 November 2000 at 3:42 PM

Well in 3d stuff, all vertices are based on the origin. The x,y,z is an offset in object space from the object's origin. This way, when poser transform/translate the object, the matrix has the object to world transform and the object's offset in the world. They just zip the vertices through this matrix and voila, world space vertices. The can also multiply matrices so, for example, the figure has a figure matrix, this times the neck matrix gives the neck in WS, this times the head matrix gives the head vertices in WS and so forth.


dke ( ) posted Tue, 07 November 2000 at 5:39 PM

It's definately not a given as far as OBJ's go. As for these particular models, I suppose it would make sense fro ZYgote to make one half then mirror it. Just because they mirror in the x direction, they certainaly don't in the other's. Not familar with this program or what it does, but I would suggest at least giving an option for the user to specify the mirroring values themselves. Plus perhaps a transformation/rotation set prior to that. Many models come in many different orientations, and that's completely at the whim of whoever made them. So they could really be anywhere, although in general people do tend to keep them near the origin. Bruce


chadly ( ) posted Wed, 08 November 2000 at 9:16 PM

Yes, nearly all of Zygote's models "face" positive Z, and if they are symmetrical left to right then they are always mirrored on absolute X. This is easy and desirable in most modeling programs. (Our models are rarely centered on any axis other than X.) And yes, this is a Zygote preference and is not a given with any model by any means. Hope this helps. -Chad Smith Zygote Media Group


duanemoody ( ) posted Thu, 09 November 2000 at 11:19 AM

Thanks, Chad. You've made my job a lot easier.


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