Where can I find the meaning of the number in the transform property from the API?

kevin_dolfing

Hello, I am doing a prototype with the OnShape API for an internship, which involves showing an assembly in GLTF on another webpage. So far I've been able to work my way through the API except this. When I get the data for an assembly I get a occurrences.transform property that looks like this: 

<div>transform: [</div><div>&nbsp; &nbsp; 1,</div><div>&nbsp; &nbsp; 0,</div><div>&nbsp; &nbsp; 0,</div><div>&nbsp; &nbsp; -0.11526866659459908,</div><div>&nbsp; &nbsp; 0,</div><div>&nbsp; &nbsp; 1,</div><div>&nbsp; &nbsp; 0,</div><div>&nbsp; &nbsp; -0.02565412583836096,</div><div>&nbsp; &nbsp; 0,</div><div>&nbsp; &nbsp; 0,</div><div>&nbsp; &nbsp; 1,</div><div>&nbsp; &nbsp; 0.01184993247305625,</div><div>&nbsp; &nbsp; 0,</div><div>&nbsp; &nbsp; 0,</div><div>&nbsp; &nbsp; 0,</div><div>&nbsp; &nbsp; 1</div><div>]</div>

How do I know what these values stand for? I've looked around, but can't seem to find any definition for these. I assume index 3, 7 and 11 are x y and z respectively, but what about the other values.

Edit: Looks like the code block didn't get posted right. So here's a hastebin link: https://hastebin.com/nogivuporo.yaml 

Edit 2: Further investigation leads me to believe that index 2, 6 and 10 represent the rotation, though these numbers don't seem to line up with radians, degrees or gradiens? Is there some catch with this?

caden_armstrong2

The transformation matrix is a 4x4 matrix comprised of a rotation matrix, translation array, uniform scale, and i think non-uniform scale(? havent confirmed this, but it doesn't matter in most use cases).

the indices
0,1,2
4,5,6
8,9,10
Are the rotation matrix.

indicies
12,13,14
3,7,11
are the translation array

index 15 is the scale parameter (default to 1)

And the indicides
3,7,11
12,13,14
I believe are non-uniform scaling, but I have tested them, these should be set to zero.
Its possible they aren't supported.

Peter Brinkhuis has written a great article about transformations specific to the solidworks api here
A lot of it applies to the onshape transform, but the indicies are in a different order.

caden_armstrong2

The transformation matrix is a 4x4 matrix comprised of a rotation matrix, translation array, uniform scale, and i think non-uniform scale(? havent confirmed this, but it doesn't matter in most use cases).

the indices
0,1,2
4,5,6
8,9,10
Are the rotation matrix.

indicies
12,13,14
3,7,11
are the translation array

index 15 is the scale parameter (default to 1)

And the indicides
3,7,11
12,13,14
I believe are non-uniform scaling, but I have tested them, these should be set to zero.
Its possible they aren't supported.

Peter Brinkhuis has written a great article about transformations specific to the solidworks api here
A lot of it applies to the onshape transform, but the indicies are in a different order.

kevin_dolfing

Thanks for the good resource @caden_armstrong. However I believe that 12,13 and 14 is the non-uniform scaling and 3, 7 and 11 is the translation array. Reason for this is that I haven't seen a single 3, 7, 11 that has been 0 from the api, while 12,13 and 14 always were. Translation matrix really was a keyword I needed. I will have a go at this

kevin_dolfing

For those who might see this in the future. I was using Three.js as a renderer and tried using the wrong Matrix4 method. I used Matrix4.fromArray, where I should have used Matrix4.set.

caden_armstrong2

@kevin_dolfing Yes you are correct.

I had it confused with the view matrix, which is transposed from the transform matrix.

stephanos_androutsellis

https://forum.onshape.com/discussion/comment/86100#Comment_86100

Thank you! That's exactly what I was looking for… :-)

nate_jake

Yeah, you’re basically looking at a 4×4 transformation matrix in row-major order — it’s the standard format used for 3D transforms (translation + rotation + scale).

So the array breaks down like this:

[   r11, r12, r13, tx,   r21, r22, r23, ty,   r31, r32, r33, tz,   0,   0,   0,   1 ]

The first 3×3 chunk (r11–r33) is your rotation (and possibly scale if any). The last column (tx, ty, tz) is your translation in meters.

If you’re sending this to a GLTF scene, you can just treat it as a standard transform matrix — most 3D engines (like three.js) have a Matrix4.fromArray() or similar that’ll accept it directly. No need to convert angles; the rotation part is already baked into the matrix, not in degrees/radians form.