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# Maintaining speed with touch path

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#1
Members - Reputation: **107**

Posted 13 March 2012 - 11:09 AM

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#3
Moderators - Reputation: **38023**

Posted 13 March 2012 - 05:03 PM

Perhaps a rolling average or weighted spline of point distances to come up with your velocity ? Or if the velocity should be kept current, you would not need to do anything other than follow the curve.

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#4
Members - Reputation: **107**

Posted 14 March 2012 - 10:38 AM

double theta = Math.atan2(pathPoints.firstElement().y-posY, pathPoints.firstElement().x - posX);

velX=(float) (magnitude * Math.sin(theta));

velY=(float) (magnitude * Math.cos(theta));

but this results in the plane moving in a straight line away from the point, in the opposite direction. I also tried doing posY-velY but this resulted in the plane flying in a circle. What am I doing wrong?

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#5
Members - Reputation: **154**

Posted 15 March 2012 - 11:59 AM

double theta = Math.atan2(nextY - posY, nextX - posX); //calculate the angle of the next coordinate relative to the current position velX = magnitude*Math.cos(theta); //calculate the velocity of X given using the angle of theta and magnitude of the total velocity velY = magnitude*Math.sin(theta); //calculate the velocity of Y given using the angle of theta and magnitude of the total velocity currX+=velX*(timeElapsed); //add the velocity to the currentX currY+=velY*(timeElapsed); //add the velocity to the currentY

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#6
Members - Reputation: **2138**

Posted 15 March 2012 - 01:53 PM

Sorry I think I was a bit unclear about my intentions. My plane has a velX and velY value that is added to the position to move it. When a path is created I'm having an issue moving the plane along to the next point. I tried :

double theta = Math.atan2(pathPoints.firstElement().y-posY, pathPoints.firstElement().x - posX);

velX=(float) (magnitude * Math.sin(theta));

velY=(float) (magnitude * Math.cos(theta));

but this results in the plane moving in a straight line away from the point, in the opposite direction. I also tried doing posY-velY but this resulted in the plane flying in a circle. What am I doing wrong?

With this code snippet, you are doing a redundant euclidean -> polar -> euclidean conversion. It is simpler and faster to just work with 2D vectors as follows:

// Unnormalized direction vector to move to. velX = pathPoints.firstElement().x - posX; velY = pathPoints.firstElement().y - posY; float length = velX*velX + velY*velY; float desiredVelocity = x; if (length <= desiredVelocity*desiredVelocity) { // distance to target is shorter than our velocity. We have arrived to our target, what to do? // Immediately snap to target, or take next waypoint instead? return; } // Scale the velocity to the desired length. length = 1.0f / Sqrt(length); velX *= length * desiredVelocity; velY *= length * desiredVelocity;

However, if I understand correctly, you are moving your plane through a set of waypoints. In that case, just going linearly from waypoint to waypoint will look jaggy, and instead, you will be looking to use a smooth curve with arc length parametrization. At least, that's what the flight control games on Android and iPad are doing.