Any existing way to project 3D points on-screen and back?

Programming Questions

noncom

Any existing way to project 3D points on-screen and back?

in Programming Questions • 3 years ago

Hi, I am developing an application, where some objects move in a 3D space. I am using OCD as a camera lib. I need to somehow be able to project mouseX and mouseY to the 3D worlds "ground" plane so that if I click the mouse, the objects may get arranged around the point and so that i can select the objects with the mouse. Also I need to be able to project a 3D point to the screen to get some objects data displayed next to the objects.

Ideally the functions would look like this:

float[3] projectPointIn3D(mouseX, mouseY);

float[2] projectPointOnScreen(x, y ,z);

I know that all this is about ray/plane intersection but it involves too much math for me to dive into it right now. Do you know any library to help me with this? Or at least any good source of information where the math is described in a digestible way?

Replies(7)

kooogy

Re: Any existing way to project 3D points on-screen and back?

3 years ago

is this what modelX() and screenX() do? i've never used them, but see the reference.

noncom

Re: Any existing way to project 3D points on-screen and back?

3 years ago

Thanks for the answer. Really, the screenX() does the second part of the job - on-screen projection

, but modelX() is somewhat completely different and is related to pushing and poping matrices.. Any more ideas?

kevin.bjo..

Re: Any existing way to project 3D points on-screen and back?

3 years ago

Sadly, it looks like Processing (and OCD) hide this level of detail from you.

Sounds lik what you want is the inverse transform. Then you could just take a vector through screen X,Y and intersect with Y=0. But first you need the matrices, which are hidden.

kb, http://www.riftgame.com/

kooogy

Re: Re: Any existing way to project 3D points on-screen and back?

3 years ago

> But first you need the matrices, which are hidden.

printMatrix() will print them. but only print them.

PGraphics3d has two matrices defined inside it called modelView and modelViewInv. they are both Public and of type PMatrix3D (which has 16 members float m00 to m33 defining the 4x4 transformation).

void setup() {
size(100, 100, P3D);
PGraphics3D p3d = (PGraphics3D)g;
println(p3d.modelview.m00);
println(p3d.modelviewInv.m00);
}

will print out the first of each. i am guessing.

noncom

Re: Any existing way to project 3D points on-screen and back?

3 years ago

Yes, i think, it is called reverse transformation... The math there is nothing more than matrices and trigonometry but i never tried to get into it really. Do you have any links for resources?

noncom

Re: Any existing way to project 3D points on-screen and back?

3 years ago

just have spotted your post, kooogy.

yes, your example prints the matrix out... however, it is still going to require some math coding dealing with the task.. and i have not yet found any texts covering this topic as it stands.

i think, i'll try to forge together the screenX() function for screening and OCDs aim() and target() with PGraphics3Ds functions for reverse transformation...

pixelnerve

Re: Any existing way to project 3D points on-screen and back?

3 years ago

GLU has 2 methods for project/unproject that gives you want you're looking for.
this page shows the code implementing those 2 methods, so you can make use of it.

http://www.opengl.org/wiki/GluProject_and_gluUnProject_code

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