CODEWITHSUNDEEP
javatrigonometry
bajen micke
bajen micke

Reputation: 319

Problems with cos and sin in Android

I have a problem with my code in Android. I am using this to moving a ball. If the degree is 90 it should move to the right, if the degree is 180 it should move down etc.

This is the code I have done.

int degrees=180;
int bollspeed=4;

bollX += bollspeed*Math.cos(Math.toRadians(degrees)); 
bollY += bollspeed*Math.sin(Math.toRadians(degrees));

The problem is that when the ball should move 90 degrees it moves 180, and when it should move 180 degrees it moves 270. I have tested all I could come to think... Can anyone see any error in my code or have a expanation I would be really glad. Thanks

Upvotes: 2

Views: 8762

Answers (3)

Jwc24678
Jwc24678

Reputation: 161

90 degrees is equivalent to π/2. The cosine of π/2 = 0. so the balls speed in the X should not change.

The sine of π/2 = 1 so the ball speed in the Y should increase by 1.

Degrees | Radians | Value

cos(0°) = cos(0) = 1

cos(90°) = cos(π/2) = 0

cos(180°) = cos(π) = -1

cos(270°) = cost(3π/2) = 0

sin(0°) = sin(0) = 0

sin(90°) = sin(π/2) = 1

sin(180°) = sin(π) = 0

sin(270°) = sin(3π/2) = -1

Upvotes: 3

ghostbust555
ghostbust555

Reputation: 2049

Why not subtract 90 degrees then?

bollX += bollspeed*Math.cos(Math.toRadians(degrees-90)); 
bollY += bollspeed*Math.sin(Math.toRadians(degrees-90));

Upvotes: 4

assylias
assylias

Reputation: 328608

How about Math.toRadians(degrees-90) ? When using polar coordinates, 0 degree is supposed to be at 3 o'clock, not at 12.

Upvotes: 9

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