Math Is Fun Forum

Thanks Ricky, the cos sin and arctan functions were/are a bit of a concern as yes they are supposed to be slow. I put it on the list of optimization issues and will test what the fastest solution is (including my silly pythagoras solution , but who knows, 10 lines of code can be faster then one line!). Would be nice to know what your findings are, if you wish to share?

Thanks a lot both of you!

Sorry, This is a line / triangle intersection in a 3D world (directx). Actually what I need to find out is the y position of a landscape at a given position for x and z. so I can place an object on the landscape. A landscape is simply a huge number of vertices. 3 vertices connected to eachother (triangle) form a face. So my thought was, if I make a vertical line with known x and z values and a low and high y value I should be able to find the y value of the landscape at intersection point.

I found this piece of code: http://www.angelfire.com/fl/houseofbartlett/solutions/line2tri.html#Code

But actually this is a bit more complex. I only have access to vertice positions. If I first search for the 3 vertices of which the x and z values are closest to the x and z values of the line and if I then check whether the line is inside the triangle formed by these 3 vertices, will it be certain that these 3 triangles do actualy form a face? I think not. I guess I will have to experiment with this and see how accurate it is in bumpy areas of the landscape.

Yes, it seems to be fine.

Still a long way to go though, but taking things step by step

Works great!

Although I had to deal with two issues (this is a directx 3d project) when the x value of B is higher then x of A then the point is flipped to the wrong side of B. When both x's are the same it also choses the wrong side by default.

Thanks a lot for responding so quick and great forum (it took me about 5 secs of googling to find it)!

Actually this is a directx 3d issue. I have 2 objects (a and b) on the scene and I would like to place the cam (object C, which will render the visible part of the 3d world) behind object b in the direction of object A. The cam is always positioned on a predefined distance of object B. So you know the positions of object A and B. In directx you work with 3 coordinates but this issue doesn't include the y (vertical) plane only horizontal and depth.

For example the coordinates of A are 50 (x) and 70 (z) and the coordinates of B are 10 (x) and 80 (z), the distance between B and C should be 5. What are the exact x and z coordinates of object C?

Actually, it would also be nice if you would have the formula for all 3 planes.

Thanks!