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  Geting XYZ of a point along a line (vector)  (Read 728 times)
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Offline pixelprime

Junior Devvie

Medals: 3

« Posted 2013-03-31 11:50:59 »

I know this may seem like a dumb question, but I'm having some odd problems when trying to calculate the position of a point in space along a vector.

My objective is to grab the XYZ coordinates of a point in space directly in front of the camera with a set distance.

I know the pitch, roll and yaw angles of the camera already, and my existing calculation looks like the following (angles in this example are originally stored as degrees, then converted into radians):

float addX = 5  * (float)Math.sin(Math.toRadians(camera.yaw));
float addZ = 5  * (float)Math.cos(Math.toRadians(camera.yaw));
float addY = 5  * (float)Math.sin(Math.toRadians(camera.pitch));

float newX = camera.x + addX;
float newZ = camera.z + addZ;
float newY = camera.y + addY;

The problem I have is that the new point - which does project in front of the camera as intended - doesn't seem to work along the Y axis correctly. It 'clamps' between the angles of -45° to +45°.

So, rotating the camera around the Y axis (yawing) seems to work great - the point 'fires' off from the camera in the right direction - but the plotting of the point in around the camera's pitch arc is out of whack!

For reference, this code is intended to be used as a line-of-sight calculation for detecting what the player is looking at.

Any help would be greatly appreciated. Thank you!
Offline quew8

JGO Knight

Medals: 46

« Reply #1 - Posted 2013-03-31 13:56:56 »

Your problem is that you've forgotten that pitch effects x, y and z values. It's very hard to explain without a diagram so I'm afraid I'm not even going to try.
Anyway here is the code I think you want:

double pitchRad = Math.toRadians(camera.pitch);
double yawRad = Math.toRadians(camera.yaw);
float f = (float)Math.cos(pitchRad);
float addX = 5  * f * (float)Math.sin(yawRad);
float addZ = 5  * f * (float)Math.cos(yawRad);
float addY = 5  * (float)Math.sin(pitchRad);

The important bit is the times f. The rest is just me absent mindedly changing code.
Please do bear in mind that I have to draw this out at least 3 times every time I try to solve the problem and I still get it wrong sometimes.
Offline pixelprime

Junior Devvie

Medals: 3

« Reply #2 - Posted 2013-04-01 14:21:55 »

Thanks for taking the time to post an example. Yes, it appears I've missed this somewhat obvious factor here, so I'll give your modifications a try and report my findings back here.

Thanks again!
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Offline pixelprime

Junior Devvie

Medals: 3

« Reply #3 - Posted 2013-04-01 19:58:10 »

I just wanted to drop a final post on to say that the code worked a treat - thank you very much!

I modified my original XYZ projection code with the coefficient cosine / sine angles and everything now behaves as expected, thanks a bundle!
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