expression to maintain scale on a 3d layer as if z = 0

[Filip Vandueren]

Hi Scott,

I think this should take care of it in most situations:

add this to the scale property of your layer:


a=toComp(anchorPoint);

c=thisComp.activeCamera;
b=c.fromComp(a);

value * b[2]/c.zoom;


You do need a camera though.

[Scott Mcdonnell]

br>Hi Filip,

Thanks for the code, that seems to still change the scale slightly as the z goes up. I found a formula for focal length which seems to work:


focalLength = 2666.67; //could be "thisComp.activeCamera.zoom;"
z =transform.anchorPoint[2];
scaleFactor = focalLength/( focalLength+ z);
[scaleFactor*100,scaleFactor*100, scaleFactor*100]


This holds the scale exactly right but the x and y of the anchor point moves as the z value changes depending on the distance from the centre. I have played around with adjusting the anchorPoint x and y too:


z = transform.anchorPoint[0];
diffX = 0; diffY = 0;
focalLength = 2666.67;
scaleFactor = ( focalLength+ z)/focalLength;
cx = 1920/2; cy = 1080/2;
px = transform.position[0];
py = transform.position[1];
dx =(px -cx)*scaleFactor; dy =(py -cy)*scaleFactor;
diffX = cx+dx-px; diffY = cy+dy-py;
[transform.anchorPoint[0] + diffX, transform.anchorPoint[1] + diffY, z]


Now it just moves when you parent it to another layer. oh well – I will keep at it!

[Filip Vandueren]

I’m not following you.
I thought you needed it to just scale so it would appear the same scale independent of z.
If you also want to move the layer with the camera, why don’t you just parent it to the camera ?

[Evan Viera]

thanks Filip, i’m having trouble getting this to evaluate for only one frame. basically i want to use the properties of the camera at the first frame only to calculate the scale. any help?

[Evan Viera]

nevermind, i got it modifying this thread’s expression

https://forums.creativecow.net/thread/227/15418

– –

cam = thisComp.activeCamera;
distance = length(sub(position, cam.position.valueAtTime(0)));
scale * distance / cam.zoom;