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Changes between Initial Version and Version 1 of Ticket #15899, comment 17

Timestamp:: Sep 11, 2024, 11:04:45 AM (14 months ago)
Author:: Tom Goddard

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Ticket #15899, comment 17

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+{{{
 Tom:
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------Original Message-----
-From: ChimeraX <ChimeraX-bugs-admin@cgl.ucsf.edu>
-Sent: Tuesday, September 10, 2024 6:02 PM
-To: goddard@cgl.ucsf.edu; Browne, Kristen (NIH/NIAID) [C] <kristen.browne@nih.gov>
-Cc: gregc@cgl.ucsf.edu
-Subject: [EXTERNAL] Re: [ChimeraX] #15899: WRL vs. GLB output
-#15899: WRL vs. GLB output
----------------------------------------+-------------------------
-          Reporter:  kristen.browne@...<mailto:kristen.browne@...>  |      Owner:  Tom Goddard
-              Type:  defect            |     Status:  assigned
-          Priority:  normal            |  Milestone:
-         Component:  Input/Output      |    Version:
-        Resolution:                    |   Keywords:
-        Blocked By:                    |   Blocking:
-Notify when closed:                    |   Platform:  all
-           Project:  ChimeraX          |
----------------------------------------+-------------------------
-Comment (by Tom Goddard):
-Hi Kristen,
-The BabylonJS __root__ node has a 180 degree rotation about y and flips z  -> -z.  I guess that is because the BabylonJS coordinate system does not  match the standard GLTF coordinate system (x axis horizontal pointing  right, y axis vertical pointing up, z axis pointing out of the screen  toward you to make right handed coordinate system). So BabylonJS adds a  __root__ node in order to convert the GLTF coordinate system to the  BabylonJS coordinate system. The ChimeraX coordinate system is the same as  GLTF.  The BabylonJS __root__ node seems to work correctly since the  orientation of the scene shown in BabylonJS matches the orientation shown  in ChimeraX.  From what I read online Blender has the y-axis pointing into  the screen and the z-axis pointing vertically in the plane of the screen,  so it is rotated 90 degrees about x relative to the GLTF and ChimeraX  coordinate systems.
-https://gcc02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fen.wikibooks.org%2Fwiki%2FBlender_3D%3A_Noob_to_Pro%2FUnderstanding_Coordinates&data=05%7C02%7Ckristen.browne%40nih.gov%7Cdbb5cc2280014feb7a0a08dcd1e44476%7C14b77578977342d58507251ca2dc2b06%7C0%7C0%7C638616025531189236%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=TDsbJe%2FU596mpfk6HOiU6r7EBz2MbAK7z%2FV4hJzjUrg%3D&reserved=0<https://en.wikibooks.org/wiki/Blender_3D:_Noob_to_Pro/Understanding_Coordinates>
-In the .glb output from ChimeraX the centering is to put (0,0,0) at the  center of the bounding box.  Why do you say the origin should be at the  "center of mass"?  What do you mean by mass?  Each triangle has weight  proportional to area?  Or the enclosed volume of uniform mass?  Do you  really want a center of mass origin instead of center of bounding box?
-Everything I see in BabylonJS with the ChimeraX .glb looks correct.
-BabylonJS puts the camera target at (0,0,0) now that I got rid of the  unused vertices that were throwing BabylonJS box calculation off.  That is  exactly what centering is intended to do.  The centering node matrix  shifts the children objects by (-160, -104, -165).  That is the amount of  shift, not the origin.  The center of the bounding box of the surface  without the centering node is (160, 104, 165) (without the negative signs)  and the centering matrix shifts in the negative direction so that the  surface center has coordinates 0,0,0 in the centering node coordinate  system.
-So everything looks exactly as it should be in BabylonJS, the ChimeraX  .glb appears correct and is being interpreted correctly by BabylongJS  (except it mishandles unused vertices including them in the bounding box  calculation).  I'm embarrassed to keep saying this, I don't understand  what problem you think the ChimeraX centered .glb has.  I don't see any  center of rotation issues in BabylonJS with this file.  Perhaps you mean  that if you strip away the centering node and work with the child surface  node then it is not centered at 0,0,0.  Of course that would be true.  Or  maybe you mean that BabylonJS is working fine but Blender is not.  I have  not looked into what Blender is doing (beyond seeing that its standard  coordinate system supposedly does not match GLTF or ChimeraX).
-Maybe you can explain the exact steps you do in BabylonJS or Blender (open  file, rotate using this exact method, rotation is not around expected
-center...) that is not behaving as you expect it to.
-    Tom
---
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-}}}
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