# Projecting a 3d point onto a plane

• August 24th, 2010, 10:26 AM
mingming8888
Projecting a 3d point onto a plane
Hi
i am working on information visualization, which use triangle projection to do it, that get n points from a higher dimensional space to a 2 dimensional space. i need to project points from an object and plot the n points in 2D. and i am going to use JAVA to write it.
First, need to select a point to project and put it on the origin, and then put the 2nd point the right distance away from the 1st point.

Second, calculate the 3rd point using the 1st and 2nd points, which form a triangle. For the remaining points, i need to pick 2 projected points and form a triangle with the remaining points.

Thank you
• August 24th, 2010, 11:53 AM
Norm
Re: Java Programming
It looks like you are looking for help with some math concepts and design vs for java programming help.
• August 25th, 2010, 02:15 AM
mingming8888
Re: Java Programming
yea, i dont know how to start doing this program....
• August 25th, 2010, 07:54 AM
Norm
Re: Java Programming
Do you have the algorithm for the program?
Given that, we can help you write the java program to implement that algorithm.
• August 25th, 2010, 10:24 AM
mingming8888
Re: Java Programming
The algorithm is
Pick a point and put it at the origin (0,0)
Put the second point to the right distance away from the 1st point (0, distance(Point 1, Point 2))
The 3rd point is the intersect of Point 1 and Point 2's circle which form a triangle with point 1 and point 2
After projected 3 points
For each remaining points
we pick 2 projected points and form a triangle with remaining point

i need a module that project 2 points and work out where is the 3rd point will go.
• August 25th, 2010, 10:58 AM
Norm
Re: Java Programming
Quote:

Put the second point to the right distance away from the 1st point (0, distance(Point 1, Point 2))
How is a point defined? x,y or ???
How do you compute the "right distance"? How is this point defined?

Quote:

The 3rd point is the intersect of Point 1 and Point 2's circle which form a triangle with point 1 and point 2
How do the circles (that implies 2 dimensions) intersect? Wouldn't there be two points where the circles intersect? What is the diameter of the circles?

Where does the java programming come in for writing this program?

Can you give an example: Two points and the third point.
• August 25th, 2010, 11:27 AM
copeg
Re: Java Programming
Quote:

Originally Posted by mingming8888
The 3rd point is the intersect of Point 1 and Point 2's circle which form a triangle with point 1 and point 2

Unless you force some constraint on the triangle/Point3, in floating point space there are an infinite number of points which satisfy this criteria. If however point 3 is equidistant from 1 and 2, you are still left with 2 solutions.
• August 25th, 2010, 11:34 AM
mingming8888
Re: Java Programming
Quote:

Originally Posted by copeg
Unless you force some constraint on the triangle/Point3, in floating point space there are an infinite number of points which satisfy this criteria. If however point 3 is equidistant from 1 and 2, you are still left with 2 solutions.

Yea, the 3rd point is equidistant from 1 and 2, so the 2 solutions are a positive and negative y, is it? then i will take the positive one. But how can i do this?
• August 25th, 2010, 11:40 AM
mingming8888
Re: Java Programming
Quote:

Originally Posted by Norm
How is a point defined? x,y or ???

yes, x and y

Quote:

Originally Posted by Norm
How do you compute the "right distance"? How is this point defined?

after point 1 is projected, the right distance is the distance between point 1 and point 2 is the distance in the original space.

Quote:

Originally Posted by Norm
Can you give an example: Two points and the third point.

For example
Point 1 is (0,0)
Point 2 is (6,0)
Point 3 is (3, 6)