Re: [Algorithms] OBBs
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Re: [Algorithms] OBBs
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From: Kent Q. <ken...@co...> - 2000-08-07 02:46:37
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I'm sorry. I don't have time right now to go back and dig up work from two years ago. I was trying to be helpful and point out that a) a long time ago, I had problems similar to those described, and b) I vaguely remember someone pointing out that THEY had discovered a problem. I hoped it was helpful. If it's not helpful to you, ignore it. That's all I can tell you right now. Pierre Terdiman wrote: > > I'm afraid I don't get it. > > You told us about the matrix made of absolute values. That one actually is > in the RAPID source, in the obb_disjoint function. And you said that taking > the absolute values was too optimistic. So, why would it work within the > RAPID code, if it doesn't work in theory according to you ? > > Confusing. > > ----- Original Message ----- > From: Kent Quirk <ken...@co...> > To: <gda...@li...> > Sent: Sunday, August 06, 2000 7:19 AM > Subject: Re: [Algorithms] OBBs > > > Because of the legal use restrictions I did not read the RAPID code, but > > reconstructed my own code from the original paper. I was extremely > > careful, and had the same problems described here -- certain > > orientations of bounding boxes that were clearly intersecting would be > > reported as disjoint. I even reconstructed it in a spreadsheet. > > > > I have not gone back to see if I could make it work. > > > > If you used the RAPID source, I believe it works properly. > > > > Kent > > > > > > Pierre Terdiman wrote: > > > > > > Are you sure about the fact it's invalid ? I would be very interested to > > > know if this is true or not. This is weird because I've used Rapid > without > > > any problem. > > > > > > ----- Original Message ----- > > > From: Kent Quirk <ken...@co...> > > > To: <gda...@li...> > > > Sent: Friday, July 21, 2000 2:33 PM > > > Subject: Re: [Algorithms] OBBs > > > > > > > Nik...@ao... wrote: > > > > > I recently finished writing a collision detection system for my > engine > > > (using > > > > > OBBs); however I have been having trouble with the system not always > > > > > detecting collisions. I tested all of the functions separately to > > > confirm > > > > > their accuracy; yet this brought no avail. I decided to work > backwards > > > to > > > > > find the bug, and I used a function from the RAPID library which > tests > > > for > > > > > disjointedness between two boxes. Here is the description of the > > > function: > > > > > > > > > > This is a test between two boxes, box A and box B. It is assumed > that > > > > > the coordinate system is aligned and centered on box A. The 3x3 > > > > > matrix B specifies box B's orientation with respect to box A. > > > > > Specifically, the columns of B are the basis vectors (axis vectors) > of > > > > > box B. The center of box B is located at the vector T. The > > > > > dimensions of box B are given in the array b. The orientation and > > > > > placement of box A, in this coordinate system, are the identity > matrix > > > > > and zero vector, respectively, so they need not be specified. The > > > > > dimensions of box A are given in array a. > > > > > obb_disjoint(double B[3][3], double T[3], double a[3], double > b[3]); > > > > > > > > > > I set up a situation in Max using two boxes, in which the collision > > > detection > > > > > failed, and I then entered the box data in by hand. The result was > that > > > > > after putting box 2 in box 1's coordinate system, the matrix B was a > 128 > > > > > degree rotation around the Z axis (or Max's Y axis). The location > of > > > box 2 > > > > > in relation to box 1 was: > > > > > T[0]= -5.853f; > > > > > T[1]= -2.173f; > > > > > T[2]= 3.842f; > > > > > And the dimensions (half-lengths) were: > > > > > Bd[0]= 2; Bd[1]= 4; Bd[2]= 4.5; > > > > > Ad[0]= 4; Ad[1]= 1; Ad[2]= 7.5; > > > > > If you set this situation up in Max, it is obvious that the two > boxes > > > > > intersect (make sure to switch the Y & Z coordinates because of the > > > > > difference in D3D and Max's CS, and multiply the half-lengths by 2 > to > > > get the > > > > > actual dimensions). Yet, RAPID's function reports that the boxes > are > > > > > disjoint. Any help would be appreciated. > > > > > > > > I too struggled with this for a long time. > > > > > > > > After I had given up, and gone to another collision system, someone > else > > > > reported that RAPID's OBB intersection algorithm (as documented) is > too > > > > optimistic in its use of absolute value. There is a matrix in the code > > > > that gets built as the absolute values of another matrix, thereby > saving > > > > some steps...but that's an invalid savings. Sadly, I can't find the > > > > reference. But I hope this points you in the right direction, or > perhaps > > > > someone else has a better memory. > > > > > > > > Kent > > > > > > > > -- > > > > > ----------------------------------------------------------------------- > > > > Kent Quirk | CogniToy: Intelligent toys... > > > > Game Designer | for intelligent minds. > > > > ken...@co... | http://www.cognitoy.com/ > > > > > _____________________________|_________________________________________ > > > > > > > > _______________________________________________ > > > > GDAlgorithms-list mailing list > > > > GDA...@li... > > > > http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list > > > > > > _______________________________________________ > > > GDAlgorithms-list mailing list > > > GDA...@li... > > > http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list > > > > -- > > ----------------------------------------------------------------------- > > Kent Quirk | CogniToy: Intelligent toys... > > Game Architect | for intelligent minds. > > ken...@co... | http://www.cognitoy.com/ > > _____________________________|_________________________________________ > > > > _______________________________________________ > > GDAlgorithms-list mailing list > > GDA...@li... > > http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list > > _______________________________________________ > GDAlgorithms-list mailing list > GDA...@li... > http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list -- ----------------------------------------------------------------------- Kent Quirk | CogniToy: Intelligent toys... Game Architect | for intelligent minds. ken...@co... | http://www.cognitoy.com/ _____________________________|_________________________________________ |
