 | | Re: Another matrix inverse question
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(...) I can see the advantages of swapping the off-diagonals for inverting the rotation(s), but that still leaves the question of how to invert translations. In a current example I'm looking at, a minifig hand, the hand is rotated 45 degrees, (...) (20 years ago, 11-Apr-07, to lugnet.cad)
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| | Re: Another matrix inverse question
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(...) Quarternions are, IMO, a bad way to do what matrices do well. For a rotation you don't need to (and shouldn't) calculate the inverse by a routine. Just transpose (swap the off-diagonals) and you have the inverse. There's no point running (...) (20 years ago, 10-Apr-07, to lugnet.cad)
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| | Re: Another matrix inverse question
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Thanks for the information, everyone. Although the test case I posted was arbitrary, I did some other tests with matrices that were used for rotations and translations. The upper-left 3x3 seemed to be OK, but the bottom row had problems. I'm (...) (20 years ago, 10-Apr-07, to lugnet.cad)
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| | LSynth Service
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Hi, all. I've taken the liberty of fiddling around with the LSynth 2 source code a little bit more to create an LSynth Service, a text-processing extension for Mac OS X that lets you run LSynth just about anywhere you can edit text. The service (...) (20 years ago, 10-Apr-07, to lugnet.cad.dev.mac, lugnet.cad.dev, lugnet.cad)
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| | Re: Another matrix inverse question
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(...) Hi Travis, Looking at the java version of your inversion routine I would guess that it will work for almost any 3x3 matrix + 1x3 translation (the 4x3 + 1 form). Where it will have problems is in matrices for which one or more of the (...) (20 years ago, 10-Apr-07, to lugnet.cad)
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| | Re: Another matrix inverse question
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(...) Sorry about that. I wrote that code so long ago that I forgot that it wasn't a fully general-purpose matrix inversion routine. (Note that it is the way it is so that it will perform better, not because I was too lazy to do the whole shebang.) (...) (20 years ago, 10-Apr-07, to lugnet.cad)
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| | Re: Another matrix inverse question
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(...) I think you've converted Travis' code properly, but just looking at the code, I'd say it's only intended to produce the inverse of the upper-left 3x3 matrix. None of the other rows or the determinant depend in any way on the 4th row, and it's (...) (20 years ago, 10-Apr-07, to lugnet.cad)
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| | Another matrix inverse question
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Hello, I read James Reynolds' question about inverse matrices and the responses with interest since I similar questions about matrix inverses. I used Travis's TCVector::invertMatrix code as the base for a Java function. Other than the change to Java (...) (20 years ago, 10-Apr-07, to lugnet.cad)
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| | Re: how does a line ends?
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(...) Now that I'm at work, I'm able to look at Microsoft's implementation of fgets for Visual Studio 2005. They do a lock on the file prior to their loop, then call _fgetc_nolock to get each character, instead of fgetc or fread. (That's an (...) (20 years ago, 9-Apr-07, to lugnet.cad, FTX)
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| | Re: how does a line ends?
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(...) I thought about using a static instead of ungetc() in the first version of readLine() that I posted. This means that you can only read from one open file at a time, but that is usually an OK restriction as long as the programmer is aware of (...) (20 years ago, 8-Apr-07, to lugnet.cad, FTX)
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| | Re: how does a line ends?
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(...) As long as you only have one character to 'unget' you could probably speed it up by introducing a static char which holds the 'ungetted' char (or null), instead of going through ungetc() -- fgetc(). OTOH, the if-statement to check if there is (...) (20 years ago, 8-Apr-07, to lugnet.cad)
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| | Re: Inverse matrix?
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The latest: (URL) (20 years ago, 8-Apr-07, to lugnet.cad.ray, lugnet.cad)
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| | Re: Inverse matrix?
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(...) Well I'll be! That works too! Thanks you guys! James (20 years ago, 8-Apr-07, to lugnet.cad.ray, lugnet.cad)
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| | Re: Inverse matrix? [DAT]
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(...) Did you mean this: [ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 ] [ 1 5 9 13 2 6 10 14 3 7 11 15 4 8 12 16 ] I have yet to try it. James (20 years ago, 8-Apr-07, to lugnet.cad.ray, lugnet.cad)
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| | Re: Inverse matrix?
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(...) I learned my matrix math from a 3d game programming book and I have no idea what the diagonals are... I was going to look it up but I got Travis' code to work! (URL) might still look it up as I may need to know about it) James (20 years ago, 7-Apr-07, to lugnet.cad.ray, lugnet.cad)
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| | Re: Inverse matrix?
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(...) I mean swap the OFF-diagonals, leave the diagonals as is. (...) (20 years ago, 7-Apr-07, to lugnet.cad.ray, lugnet.cad)
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| | Re: how does a line ends?
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(...) Interesting. I looked at the C runtime library sources that came with MSVC++ 6.0. The fgets() function there is definitely a little different than either yours or the one ROSCO linked. It does have a couple calls for thread safety, but (...) (20 years ago, 7-Apr-07, to lugnet.cad, FTX)
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| | Re: Inverse matrix?
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(...) Just take the transpose of the 3x3 world rotation matrix and it should work as the inverse. Transpose means swap diagonals M[1,2] <=> M[2,1] etc. If this doesn't work I've misunderstood you. Tim (20 years ago, 7-Apr-07, to lugnet.cad.ray, lugnet.cad)
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| | Re: Inverse matrix?
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(...) Hehehe, cool, I'll try that. Thanks! James (20 years ago, 7-Apr-07, to lugnet.cad.ray, lugnet.cad)
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| | Re: Inverse matrix?
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Clarification! .... snip (...) I am using additional points to specify the location of feet. Combined with the model location, I have 3 points for the hip and feet. [now the following paragraph should make more sense] (...) (20 years ago, 7-Apr-07, to lugnet.cad.ray, lugnet.cad)
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