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7.8

sine/cosine inaccuracies

Asked by GabeSmed in C++ Programming Language

Tags: cosine, sine

Hi there everyone.  I've been using the C++ sin() and cos() functions to get the x and y coordinates from a direction and speed variable.  Now, I have noticed that when I use these and the speed (float) variable is fairly low (0 to, maybe, 50 ish) the functions behave very strangely.  First, here is the code I use:

car.x += (int)((speed * cos(direction * 3.1415926535 / 180)) / SCALE_FACTOR); //everything reduced
            car.y += (int)((speed * sin(direction * 3.1415926535 / 180)) / SCALE_FACTOR); //by a factor of 15

car.x and .y are integers; I cannot change that.  Direction is a float between 0 and 359.99... and speed is a float from 0 up.  the SCALE_FACTOR is currently 15.

what happens is this.  If the angle is far from pointing left,right,up, or down, at low speeds my car moves in a sort of zigzag pattern, going first left, then up, then left, then up, until it reaches a certain speed where it then goes normally.  If the angle is close to those four angles, at low speeds the car simple goes straight left (or up, or down, or right) until it reaches a certain speed where it performs normally.

If i'm not being clear I can email you the program in question so you can look at the effects yourselves.  Thanks in advance.
 
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[+][-]05/14/00 03:35 AM, ID: 2808082Accepted Solution

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Zone: C++ Programming Language
Tags: cosine, sine
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Solution Provided By: ozo
Participating Experts: 3
Solution Grade: B
 
[+][-]05/13/00 10:46 PM, ID: 2807832Expert Comment

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[+][-]05/13/00 11:36 PM, ID: 2807893Expert Comment

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[+][-]05/14/00 05:53 AM, ID: 2808259Expert Comment

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[+][-]05/14/00 08:53 AM, ID: 2808505Author Comment

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