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# Weired Acis transformation matrix

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### #1dgcoventry  Members   -  Reputation: 184

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Posted 16 April 2011 - 01:36 AM

I have queried an ACIS solid in AutoCAD using autolisp and have extracted what appears to be a transformation matrix:

transform $-1 0.965925826289068 -0.258819045102521 0 0.258819045102521 0.965925826289068 0 0 0 1 -1.63832380999416 3.11204436836534 0 1 rotate no_reflect no_shear # Dose anyone recognise this kind of entity? It sort of looks like a 4x4 transformation matrix (regarding the 0 0 0 1 line in the middle), but the arguments only have fourteen reals. ### #2haegarr Crossbones+ - Reputation: 7160 Like 1Likes Like Posted 16 April 2011 - 02:55 AM No documentation found, but a transform description can be anything (see e.g. the transform node of X3D). transform$-1 0.965925826289068 -0.258819045102521 0 0.258819045102521 0.965925826289068 0 0 0 1 -1.63832380999416 3.11204436836534 0 1 rotate no_reflect no_shear #

I'd say that
0.965925826289068 -0.258819045102521 0
0.258819045102521 0.965925826289068 0
0 0 1
is a 3D rotation by 15 degree around the z axis, given as a affine matrix. I'd further assume that the subsequent
1.63832380999416 3.11204436836534 0
defines a affine position. I have no clue what the leading -1 and trailing 1 mean. The latter one may perhaps be a scaling factor, but then for uniform scaling only. If you want to investigate this w/o having access to a documentation, try to apply well known transformations and look at the resulting numbers.

### #3dgcoventry  Members   -  Reputation: 184

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Posted 17 April 2011 - 03:20 PM

No documentation found, but a transform description can be anything (see e.g. the transform node of X3D).

transform \$-1 0.965925826289068 -0.258819045102521 0 0.258819045102521 0.965925826289068 0 0 0 1 -1.63832380999416 3.11204436836534 0 1 rotate no_reflect no_shear #

I'd say that
0.965925826289068 -0.258819045102521 0
0.258819045102521 0.965925826289068 0
0 0 1
is a 3D rotation by 15 degree around the z axis, given as a affine matrix. I'd further assume that the subsequent
1.63832380999416 3.11204436836534 0
defines a affine position. I have no clue what the leading -1 and trailing 1 mean. The latter one may perhaps be a scaling factor, but then for uniform scaling only. If you want to investigate this w/o having access to a documentation, try to apply well known transformations and look at the resulting numbers.

Thanks Haegarr,

That does sound very likely.

I have searched for documentation on this but have been unable to find any.

I'll do what you suggest and see if the numbers tally.

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