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dgcoventry

Weired Acis transformation matrix

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

[quote]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 # [/quote]

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.

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

[quote]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 # [/quote]
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.

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[quote name='haegarr' timestamp='1302944134' post='4799071']
No documentation found, but a transform description can be anything (see e.g. the transform node of X3D).

[quote]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 # [/quote]
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.
[/quote]

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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