Code An Aim Constraint

[starrider]

hey there!
for my plugin i have to convert a velocity vector and an up vector to a euler rotation. it's almost the same as using the aim-constraint of maya, but that's not possible. does anybody now how to code this?
currently i got it two rotation axis, but the third doesn't orient towards the up-vector (i don't know how to code that). so here's what i got (still in mel) - pCube is constraint to the vector which is described by the locator/worldCenter:

CODE
$locPos = <>;
pCube1.rotateZ = atan($locPos.y / $locPos.x) * 57.296;
if($locPos.x < 0)
    pCube1.rotateZ = pCube1.rotateZ -180;
pCube1.rotateY = atan(-$locPos.z / sqrt($locPos.x*$locPos.x+$locPos.y*$locPos.y)) * 57.296;

would be very helpful!

greets

daniel

[raaajjj]

Hi.

if
QUOTE
pCube is constraint to the vector which is described by the locator/worldCenter:

then use this expression to get the constraint result
CODE
vector $pos = getAttr locator1.translate;
float $rot[] = angleBetween -euler -v1 0.0 1.0 0.0 -v2 ($pos.x) ($pos.y) ($pos.z);
setAttr pCone1.rotate ($rot[0]) ($rot[1]) ($rot[2]);

for particles use
CODE
vector $pos = particleShape1.worldVelocity;

and in the angleBetween command use up vector for the parameter -v1

Hope this helps...

[starrider]

hi!
first: thanks for you help!
i tried that one, but it gave me the same result as before, because it only orients one axis towards the aim-vector but doesn't work with an up vector. i want to aim the x-axis of an object along one vector and the y-axis towards the scene up (which can't always be reached - but as near as possible) - the same as an aim-constraint with scene-up as up-vector:

CODE
aimConstraint -aimVector 1 0 0 -upVector 0 1 0 -worldUpType "scene";

but coded and not using the constraint... :[
and ... i have to do it in c++-api. i'm just testing in mel...
i'll keep on trying!
cheers

[daniel-faust]

CODE
    // Get the position of the target point.

    MDataHandle mdhTarget = mdbData.inputValue(m_moTarget);
    MMatrix mmTarget = mdhTarget.asMatrix();
    MPoint mpTarget(mmTarget[3][0], mmTarget[3][1], mmTarget[3][2]);

    // Get the inverse transformation matrix of this node:

    MDagPath mdpThis;
    MFnDagNode mfdnThis(thisMObject());
    mfdnThis.getPath(mdpThis);
    MMatrix mmMatrix = mdpThis.inclusiveMatrix();
    MMatrix mmMatrixInverse = mmMatrix.inverse();

    // Express the target point in this node's object space:

    MPoint mpTargetInThisSpace(mpTarget * mmMatrixInverse);

    // Assuming that the vector 1, 0, 0 defines the position of the front of this node,
    // get the quaternion that describes the rotation to make that vector point to mpTargetInThisSpace:

    MQuaternion mqToTarget(MVector(1.0,0.0,0.0).rotateTo(MVector(mpTargetInThisSpace)));

    // Apply that rotation to this node:

    MFnTransform mftThis(mdpThis.transform());
    mftThis.rotateBy(mqToTarget, MSpace::kPreTransform);

    // Get the new inverse transformation matrix of this node

    /*MMatrix*/ mmMatrix = mdpThis.inclusiveMatrix();
    /*MMatrix*/ mmMatrixInverse = mmMatrix.inverse();

    // Get the world up vector.

    MDataHandle mdhUp = mdbData.inputValue(m_moUpX);
    MVector mvUp = mdhUp.asVector();

    // Express the world up vector in this node's object space.

    MPoint mpWorldUpInThisSpace(mvUp * mmMatrixInverse);

    // Get the quaternion that describes the rotation to make the local up vector point to the world up vector:
    MQuaternion mqToWorldUp(MVector(MVector(0.0, 1.0, 0.0)).rotateTo(MVector(mpWorldUpInThisSpace)));

    // Get the x-axis rotation from the quaternion
    MEulerRotation merToWorldUp(mqToWorldUp.asEulerRotation());
    merToWorldUp.y = 0.0;
    merToWorldUp.z = 0.0;

    // Apply that rotation to this node:
    mftThis.rotateBy(merToWorldUp, MSpace::kPreTransform);

Hope it helped.

[starrider]

hi!
thank you very much! it was very helpful. i implemented it similar to your way (i had to change some lines because my node has to output a k3Double to connect it directly to another transform node). everything went well - then i decided to write a little command to make it availabe for using it in daily live. and there i discovered that the x-rotation flips when the aim-vectors X is below zero and the Z comes from minus to plus.
here's my code i did:

CODE
// vAim = aim - Vector
// vUp    = up - Vector

MEulerRotation erResult;

// i removed the first space conversation because i'm always in world space in my case
MQuaternion qToTarget(MVector(1.0,0.0,0.0).rotateTo(vAim));
erResult = qToTarget.asEulerRotation();

// world space-matrix
MMatrix m = MMatrix::identity;

// rotate to the new space
m *= qToTarget.asMatrix();
MMatrix mInv = m.inverse();

// convert up-vector to new space
MVector mvYinThisSpace = (MVector)(vUp * mInv);

// and rotate it
MQuaternion mqToWorldUp((MVector(0.0, 1.0, 0.0)).rotateTo(mvYinThisSpace));

MEulerRotation merToWorldUp(mqToWorldUp.asEulerRotation());
merToWorldUp.y = 0.0;
merToWorldUp.z = 0.0;

// add the two rotations
erResult += merToWorldUp;

i think it should deliver the same result as yours...
you can find the command-plugin, a test-scene and the cpp-file HERE.
maybe you or someone else would know how to fix that!
but thanks to you anyway!

[daniel-faust]

The problem is that you are missing one more parameter to your command.

Draw two points on a piece of paper, separated at about 2 cm from each other. Take a postit note. Cut the postit note diagonally. Align it in such a way, that one of the two shortes sides of the note touches one point, and the other short side the other point.

You will see that there are multiple solutions to this problem while you rotate the postit slightly.

Take a new paper. Draw three points on the new paper. Label one of those points pCone1 and another one locator1(=aim) and draw a straight line between the two labeled points. Take the postit note and align one of the short sides parallel to the drawn line, and move it front or back until you touch the third point with the other short side.

This time you have only one solution.

My recommendation is that you change the command to be used as follows
vector $res = vec2rot -aim ... -up ... pCone1;
this way you have full access to the pCone1 object inside of the command and can extract the position of it for the calculations.

[starrider]

i finally solved it ...
if i got vAim and vUp i first have to calculate the my new axis,

CODE
vX = vAim.normal();
vZ = vUp.normal()^vAim.normal();  // the vector which is orthogonal to my aim and up
vY = vAim.normal()^vZ.normal(); // the vector which is my new up and orthogonal to vX and vZ

from this i'm able to create a 4x4 matrix containing the local coordinate system of my object:
CODE
double daTemp[4][4];

daTemp[0][0] = vX.x; daTemp[0][1] = vY.x; daTemp[0][2] = vZ.x; daTemp[0][3] = 0.0;
daTemp[1][0] = vX.y; daTemp[1][1] = vY.y; daTemp[1][2] = vZ.y; daTemp[1][3] = 0.0;
daTemp[2][0] = vX.z; daTemp[2][1] = vY.z; daTemp[2][2] = vZ.z; daTemp[2][3] = 0.0;
daTemp[3][0] = 0.0; daTemp[3][1] = 0.0; daTemp[3][2] = 0.0; daTemp[3][3] = 1.0;

MMatrix mFinal(daTemp);

... then i have to get the rotation matrix, which converts my default maya coordinate system...
CODE
MMatrix mOrig;
mOrig = mOrig.setToIdentity();

... to my new one:
CODE
MMatrix mRot = mFinal * mOrig.inverse();

... set the rotation order of my resulting euler-rotation to maya default (ZYX)
CODE
erResult.reorderIt(MEulerRotation::RotationOrder::kZYX);

and convert the matrix to my result
CODE
erResult = mRot;

the y and x axis are switched - i don't know why, but everythin works fine if i negate them before starting the calculation.
yippee - i'm happy know.
thanks to you guys!

cheers