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POI understand that Sin and Cos are in radians, but why I am still off by 90 degrees?
 

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  1. POI understand that Sin and Cos are in radians, but why I am still off by 90 degrees?
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    <p>Let's say I have the values X = 0, Y = 0 and I want to calculate a new point (X1, Y1) from a vector and a magnitude. Let's say the vector is 90 degrees (not radians) and the magnitude is 10 so the code would look something like this:</p> <pre><code>x1 = X + (10 * Math.Cos(90 * (Math.PI / 180.0))); y1 = Y + (10 * Math.Sin(90 * (Math.PI / 180.0))); </code></pre> <p>And I then draw a line to confirm the results</p> <pre><code>DrawLine(X,Y,x1,y1); </code></pre> <p>But my line is off by 90 degrees too much! If I subtract 90 from the angle that I'm passing to Cos and Sin everything works out fine. So, I guess, I can live with that.</p> <p>Here's a screen shot: <img src="https://i.stack.imgur.com/TkAR7.jpg" alt="enter image description here"></p> <p>I'm passing it 90 and I'm expecting the line to go west - east. I assume that 0 degrees is due north. I know that the coordinate system I'm using is X is horizontal and Y is vertical. </p> <p>I'm just curious as to what I'm missing.</p>
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    1. USzetar
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    1. COYour code looks fine to me. What direction does your vector point (use north/south/east/west so we can imagine it too) and what direction did you expect it to point?
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      1. POI understand that Sin and Cos are in radians, but why I am still off by 90 degrees?
      1. USGreg Hewgill
    2. COPerhaps you can show a screenshot of what it looks like and what you expect it to look like
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      1. POI understand that Sin and Cos are in radians, but why I am still off by 90 degrees?
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    3. COHow are you measuring the angles? The trig functions expect that theta=0 corresponds to the +X axis (East), with theta increasing in the counter-clockwise direction. For compass headings, theta=0 corresponds to due north, and increases clockwise.
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      1. POI understand that Sin and Cos are in radians, but why I am still off by 90 degrees?
      1. USJim Lewis
 

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