[osg-users] about the bounding sphere of a geode computed by OSG
Hi All, I'm having problem computing the global bounding sphere of my model. I debugged OSG (2.8.0) and discovered that the bounding sphere of a geode (BoundingSphere Geode::computeBound()) is computed as the bounding sphere of the bounding box that includes all its drawables !?! Why that? Shouldn't it be the global bounding sphere of the drawables, merging the single bounding spheres of all the drawables? So, a drawable that represents a sphere should have as bounding sphere itself, but this is not true with the computation OSG performs. It is larger than strictly required. Thanks, Gianluca Natale ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] about the bounding sphere of a geode computed by OSG
Calculating the perfect bounding sphere is an expensive operation. You need to calc the convex hull which is O(n log n). osg uses a fast approximation which is generally good enough. 2009/8/11 Gianluca Natale gianluca.nat...@adstorino.it: Hi All, I’m having problem computing the global bounding sphere of my model. I debugged OSG (2.8.0) and discovered that the bounding sphere of a geode (BoundingSphere Geode::computeBound()) is computed as the bounding sphere of the bounding box that includes all its drawables !?! Why that? Shouldn’t it be the global bounding sphere of the drawables, merging the single bounding spheres of all the drawables? So, a drawable that represents a sphere should have as bounding sphere itself, but this is not true with the computation OSG performs. It is larger than strictly required. Thanks, Gianluca Natale ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org -- http://www.ssTk.co.uk ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] about the bounding sphere of a geode computed by OSG
I cannot completely agree. I mean that I know that the real perfect bounding sphere is computationally expensive, but in many cases (solid objects) it should be computed just once (since BoundingSphere node::getBound() checks if the bounding sphere has been already computed), when the object is created. The global bounding sphere might affect the fitting operation a lot. In case of objects like spheres or discs, the bounding sphere computed by OSG might be much greater than strictly required. -Original Message- From: osg-users-boun...@lists.openscenegraph.org [mailto:osg-users-boun...@lists.openscenegraph.org] On Behalf Of Simon Hammett Sent: martedì 11 agosto 2009 12.00 To: OpenSceneGraph Users Subject: Re: [osg-users] about the bounding sphere of a geode computed by OSG Calculating the perfect bounding sphere is an expensive operation. You need to calc the convex hull which is O(n log n). osg uses a fast approximation which is generally good enough. 2009/8/11 Gianluca Natale gianluca.nat...@adstorino.it: Hi All, Im having problem computing the global bounding sphere of my model. I debugged OSG (2.8.0) and discovered that the bounding sphere of a geode (BoundingSphere Geode::computeBound()) is computed as the bounding sphere of the bounding box that includes all its drawables !?! Why that? Shouldnt it be the global bounding sphere of the drawables, merging the single bounding spheres of all the drawables? So, a drawable that represents a sphere should have as bounding sphere itself, but this is not true with the computation OSG performs. It is larger than strictly required. Thanks, Gianluca Natale ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org -- http://www.ssTk.co.uk ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.392 / Virus Database: 270.13.49/2295 - Release Date: 08/10/09 18:19:00 ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] about the bounding sphere of a geode computed by OSG
Like ALL scene graphs out there the OSG uses an approximation ( for Scenegraph performance reasons) to produce a bounding sphere that is ensured to encompass all its children but not necessarily tightly, and this is fine for 99% of bounding sphere usage in a scene graph If you want a tight and much more accurate bound sphere and or bounding box then you will need to calculate this your self Gordon Product Manager 3d __ Gordon Tomlinson Email : gtomlinson @ overwatch.textron.com __ From: osg-users-boun...@lists.openscenegraph.org [mailto:osg-users-boun...@lists.openscenegraph.org] On Behalf Of Gianluca Natale Sent: Tuesday, August 11, 2009 4:32 AM To: Osg Users Subject: [osg-users] about the bounding sphere of a geode computed by OSG Hi All, I'm having problem computing the global bounding sphere of my model. I debugged OSG (2.8.0) and discovered that the bounding sphere of a geode (BoundingSphere Geode::computeBound()) is computed as the bounding sphere of the bounding box that includes all its drawables !?! Why that? Shouldn't it be the global bounding sphere of the drawables, merging the single bounding spheres of all the drawables? So, a drawable that represents a sphere should have as bounding sphere itself, but this is not true with the computation OSG performs. It is larger than strictly required. Thanks, Gianluca Natale ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] about the bounding sphere of a geode computed by OSG
This is how it is in OSG and all other Scene graphs I have ever worked with and I have work with most Without meaning to sound rude, I would say Get used to it in OSG as it not likely to change in how's its done Gordon Product Manager 3d __ Gordon Tomlinson Email : gtomlinson @ overwatch.textron.com __ -Original Message- From: osg-users-boun...@lists.openscenegraph.org [mailto:osg-users-boun...@lists.openscenegraph.org] On Behalf Of Gianluca Natale Sent: Tuesday, August 11, 2009 6:36 AM To: 'OpenSceneGraph Users' Subject: Re: [osg-users] about the bounding sphere of a geode computed by OSG I cannot completely agree. I mean that I know that the real perfect bounding sphere is computationally expensive, but in many cases (solid objects) it should be computed just once (since BoundingSphere node::getBound() checks if the bounding sphere has been already computed), when the object is created. The global bounding sphere might affect the fitting operation a lot. In case of objects like spheres or discs, the bounding sphere computed by OSG might be much greater than strictly required. -Original Message- From: osg-users-boun...@lists.openscenegraph.org [mailto:osg-users-boun...@lists.openscenegraph.org] On Behalf Of Simon Hammett Sent: martedì 11 agosto 2009 12.00 To: OpenSceneGraph Users Subject: Re: [osg-users] about the bounding sphere of a geode computed by OSG Calculating the perfect bounding sphere is an expensive operation. You need to calc the convex hull which is O(n log n). osg uses a fast approximation which is generally good enough. 2009/8/11 Gianluca Natale gianluca.nat...@adstorino.it: Hi All, I'm having problem computing the global bounding sphere of my model. I debugged OSG (2.8.0) and discovered that the bounding sphere of a geode (BoundingSphere Geode::computeBound()) is computed as the bounding sphere of the bounding box that includes all its drawables !?! Why that? Shouldn't it be the global bounding sphere of the drawables, merging the single bounding spheres of all the drawables? So, a drawable that represents a sphere should have as bounding sphere itself, but this is not true with the computation OSG performs. It is larger than strictly required. Thanks, Gianluca Natale ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph. org -- http://www.ssTk.co.uk ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.392 / Virus Database: 270.13.49/2295 - Release Date: 08/10/09 18:19:00 ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] about the bounding sphere of a geode computed by OSG
Gianluca Natale wrote: I cannot completely agree. I mean that I know that the real perfect bounding sphere is computationally expensive, but in many cases (solid objects) it should be computed just once But in many other cases (dynamic geometry) it must be computed each frame. So it really does need to be very fast. If you need a very tight bounding sphere, you could write your own NodeVisitor to create it. But changing OSG to compute and use tight bounding spheres throughout would be a formidable redesign that could take 2-4 engineering months to completely code and test, and while it might improve culling in some cases, it would also harm performance in other cases, so the net result would probably be a wash. -Paul ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
