**Problem with transformation matrices on some parts**

2023-04-08, 9:07 (This post was last modified: 2023-04-08, 9:21 by Florentin.)

Howdy!

I hope I am on the correct forum with this post

So I am trying to program a 3d viewer for my files for my website. And I got most stuff working, but now I noticed that when loading some parts, such as 4733 (Brick, Modified 1 x 1 with Studs on 4 Sides), two of the studs are oriented the wrong way (as you can see in the picture i uploaded): they are flipped on their axes, the other studs aren't though.

And so I looked into the ldr file of the part 4733 itself where the studs themselves are being rotated (line 116-120) and I noticed that the studs that are wrongly rotated on my viewer are the 2nd and 5th entry (line 117 and 120) there. And I looked at their transformation matrices and they seem kinda wrong.

So I looked into those matrices more and it kinda looks like the axis that those matrices flip (which is what the "-" does), should be on the other axis, so the entry in line 117 should actually be "1 16 10 10 0 0 1 0 -1 0 0 0 0 1 stud2a.dat" and in line 120 it should be "1 16 0 10 10 1 0 0 0 0 -1 0 1 0 stud2a.dat".

The matrices look like the creator of the ldr part switched up the matrix multiplication, like the flipping of the two axes and the invertion of the axis, cause if you take those matrices apart and switch them around (you flip the part where the "-" is as explained above) you end up with the correct transformation matrix.

Is it normal that those matrices are just wrong? Or do I not completely understand the ldraw standard in a way that you can't just take the vertices and transform them using those matrices?

Thanks for your help!

(I also have some problems with some of the "4-4ndis.dat" transformations in this and a few other parts, though I haven't looked into that yet, you can kinda see it on the attached picture though that the scaling in the y direction is wrong, might just be an error in my code who knows, I'll look into that )

(If I haven't explained some stuff properly feel free to ask!)

(If you want to look at the code I wrote for this: link, but it's not optimised yet and I've commented some stuff out since I work directly in the deployment branch and the zip library makes my automatic deployment fail xD)

I hope I am on the correct forum with this post

So I am trying to program a 3d viewer for my files for my website. And I got most stuff working, but now I noticed that when loading some parts, such as 4733 (Brick, Modified 1 x 1 with Studs on 4 Sides), two of the studs are oriented the wrong way (as you can see in the picture i uploaded): they are flipped on their axes, the other studs aren't though.

And so I looked into the ldr file of the part 4733 itself where the studs themselves are being rotated (line 116-120) and I noticed that the studs that are wrongly rotated on my viewer are the 2nd and 5th entry (line 117 and 120) there. And I looked at their transformation matrices and they seem kinda wrong.

So I looked into those matrices more and it kinda looks like the axis that those matrices flip (which is what the "-" does), should be on the other axis, so the entry in line 117 should actually be "1 16 10 10 0 0 1 0 -1 0 0 0 0 1 stud2a.dat" and in line 120 it should be "1 16 0 10 10 1 0 0 0 0 -1 0 1 0 stud2a.dat".

The matrices look like the creator of the ldr part switched up the matrix multiplication, like the flipping of the two axes and the invertion of the axis, cause if you take those matrices apart and switch them around (you flip the part where the "-" is as explained above) you end up with the correct transformation matrix.

Is it normal that those matrices are just wrong? Or do I not completely understand the ldraw standard in a way that you can't just take the vertices and transform them using those matrices?

Thanks for your help!

(I also have some problems with some of the "4-4ndis.dat" transformations in this and a few other parts, though I haven't looked into that yet, you can kinda see it on the attached picture though that the scaling in the y direction is wrong, might just be an error in my code who knows, I'll look into that )

(If I haven't explained some stuff properly feel free to ask!)

(If you want to look at the code I wrote for this: link, but it's not optimised yet and I've commented some stuff out since I work directly in the deployment branch and the zip library makes my automatic deployment fail xD)