Project Curve Onto Surface

[bradon]

how to do a camera projection to shoot a curve onto a surface. it seems ive done this a thousand times before but now its not working properly for me. Im not sure why? here is a picture of the bad project.

http://i245.photobucket.com/albums/gg54/br...rojectcurve.png

you can see i have not moved the camera and the projection is to the right of the actual curve and doesnt line up like it should.

i have a very specific pattern that i want to line up at a certain camera angle and there are many curves so its important that they are accurate.

so i make sure to have project along active view and use a local tolerance of 0.1 select curve range complete.

am i missing something or is this just not going to work the way that i want it to?

looks like it works with an "orthographic" camera but thats not what i need it to do... so is there a way to do with a perspective camera?

[ronviers-viers]

Unless you use an orthogonal view, your results will be unpredictable. You could select and orthogonal camera to make the projection but use the perspective view to do the alignment.

[bradon]

ugg thats not what i wanted to hear. can you explain why its unpredicable to shoot a projection from a perspective camera. it seems like this should work in the same way as project a texture onto a surface with a camera. i can see myself spending hours setting up an orthogonal camera to project and then tweeking every little point and curve by hand so it matches up in the perspective view. id like to find an easier way?

[joojaa]

I can't actually verify its unpredictable. It does exactly what they tell it does project along a vector.

Anyway what build of maya are yu on? Threes afew nurbs broken builds around.

Theres a alternatuve method you can test if you need camera projection, you can actually camera deform teh object into a orthographic viewport and then project as if it was a camera angle.

[ronviers-viers]

That reply was poorly worded and did seem to imply that I knew what the hell I was talking about. What I should have said is that I have been projecting many curves on surfaces lately and I have found only the orthogonal views to be useful. A lot of times I find that I have more success if I loft a surface through the surface then work with intersection.

[bradon]

im using maya 2009 on mac os 10.4.11

thanks for the replies. Im not sure how to camera deform an object but maybe i can look it up somewhere.

as far as lofting the surfaces that might be a way to wysiwyg way to go about it. the loft curves might not extrude backwards in space perfectly perpendicular to the origional curve. cause curves in space will converge using a perspective view.

maybe ill try to project a texture map onto the surface and re-draw the curves? that seems to be the easiest method to me at this point.

[joojaa]

QUOTE(bradon @ 01/28/09, 08:13 PM) [snapback]299823[/snapback]
Im not sure how to camera deform an object but maybe i can look it up somewhere.

Attach a laticce node to it and then connect the inverse world magtrix from camera to the laticces matrix input

[joojaa]

Come to think of it its probably easier to project the curve far away in camera space loft the 2 curves together and intersect the plane. It would be easier to use and comparavbly easy to script.

[bradon]

thanks for the responses.

well i tried camera mapping the lattice as you suggest. i only see the worldIverseMatrix for the camera object and not the lattice so i cant figure out the connection there. I tried the looking at both the lattice and the lattice base with no sight of the world matrix input.

ok but the second suggestion seemed to work out ok. i just put a null under the camera and dupe all curves and put them under the null then scale the null up so the curves fly back in space and scale at the same rate allowing the curves to project perpendicular back in space perfectly. then loft all surfaces and intersect with the ground plane to make project curves on surfaces. good.

I would not mind knowing the first route though sounded like an interesting technique that ive not tried anything like that. also the fact that i have to loft all the surfaces first and trim kind of a few more steps maybe than just doing the camera matrix map technique?

[joojaa]

QUOTE(bradon @ 01/31/09, 09:09 PM) [snapback]300024[/snapback]
I would not mind knowing the first route though sounded like an interesting technique that ive not tried anything like that.

Actually you have all the time millions of times in fact (assuming you have played 3d games for more than 10 hours), that's how 3d cameras work they transform the object into a xy plane where z is straight backwards this makes calculating the things just a easy look up, and z is residual. So now drawing is just a matter of sorting the polygons. Or drawing in arbitrary order and using z buffer to decide what is in front.

Now front tarnsfroms nothing so you can transform everything into front just liek any camera.

Observe, let us asume this scene. asete into script editor and execute
CODE
file -f -new;
polyCube;

See how the cube is slanted, go to front view. Affter this apste and execute:

CODE
lattice  -divisions 2 2 2 -objectCentered true  -ldv 2 2 2;
connectAttr -f perspShape.worldInverseMatrix[0] ffd1.deformedLatticeMatrix;

Now the cube will no longer be right in preps view (tough the lattice shape will and it can act as a way to compare, pan teh view see how the front behaves, it can help to shade both to se differece between latices cage and cube) But surprisingly it looks as if looked trough preps in front. And that's how your camera internally works.

Ok so the matrix i read doesnt include the persp shrinkage coefficient but its easy to multiply in.*

Hope you learned something (ps you ca attach your own matrix for mighty weird projections if you wish, oly it doenst work quite right for raytracing unless you can freeze normals. This is not entirely easy normals dont transform right.)

PS: if you want later to add stuff to thsi new projection make the latices outside lattice attribute to be all.then just adds tuff to the set. The bonus tools uses something mucjh like this for making custom orthorgraphical views. Wahre you can manually am each axis.

PPS: results vary across versions.

*theres a cavat to this maya doesnt like to calculate the point matrix on all tiers at all times. Wich si why results vary across versions.

[bradon]

wow! thats super interesting. never would have considered anything like that that.

just noticing one resemblence of this looks very much similar to making a new ortho camera and parenting it to the persp camera. the angle and view through the camera is the same but its just flattened. i.e. no shrinkage.

I guess you mention a way to include the shrinkage as some multiplier or coeficient. Ill have to consider the first part of this more deeply to understand the second part. my mind is still blown. thanks