Matrix computing

Questions
1

Hi,
I dont’ really understand what is happening . I am trying to compute matrix, and for unknown reason, I don’t get expected results:

        const origin = new TransformNode("orig");
        origin.position.x = 5;
        const frameOrigin = origin.computeWorldMatrix(true);
        const A = new TransformNode("A");
        A.parent = origin;
        A.position.x = 25;
        const frameA = A.computeWorldMatrix(true);
        const B = new TransformNode("B");
        B.parent = A;
        B.position.x = 2;
        const frameB = B.computeWorldMatrix(true);
        console.log("mat B Tx +32", frameB);

result : !!! Tx is negative in the matrix and gives wrong result => -32 !

2

Hi, I don’t notice a problem, getTranslation returns (32, 0, 0), as expected :thinking: (see console in attached playground)

3

same
image

4

I really don’t understand. I copied elsewhere the code, same result…
this is a typescript project. version babylonjs 6.45.1

image
image949×166 9.58 KB

5

I think I found the issue. I had duplicated creation of transformnodes with same names.

6

No, … I have again negative value … :sleepy:

7

euh…looks like these are not homogenous matrix as I think.
There are impacted by camera I think.
This is very boring , since I want to retrieve frame matrix and make some robotics computations.

I would need to convert coordinates of points in some other transformnodes local spaces

8

Maybe at some point in your code you call invert() on the matrix ? It works in place, and I’m not sure the web console evaluate the matrix element before you unroll it.

Maybe try to log frameB._m.toString() ? So you’re sure it has not been changed after the log.

9

No, I checked .
What I am trying to achieve is similar to the ikbonecontroler , but I don’t want to use it for some reasons and use my own ik solver.
After I had a look at it. I found that the guy made a copy of all it s transformations matrix inside it s ik api instead of using babylonjs api matrix.
Regarding babylonjs implementation it makes sense…otherwise it is really a pain.

I really don’t understand why camera is coupled in world manipulation matrix !

10

I made something similar to IK solving here , without using built in IK solver, maybe that looks like your case.

I went knowing the length and direction of each limb part, and generating the appropriate position and rotationQuaternion for each limb part. I found it easier to understand than matrix multiplication.

If that’s helpful, the Leg code is here sumuqan/src/Leg.ts at main · SvenFrankson/sumuqan · GitHub , quaternion generation code is here mummu/src/Quaternion.ts at main · SvenFrankson/mummu · GitHub

1 Like
11

That is clean :-).
I understand, either implement another own class and matrix manipulations.
or switch to threejs , using threejs my work already works, but I have to stick it into a babylonjs project