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Rotation Interpolation

Asked 2010-04-25T14:07:21.950
39

NB: I'll present this question in degrees purely for simplicity, radians, degrees, different zero-bearing, the problem is essentially the same.

Does anyone have any ideas on the code behind rotational interpolation? Given a linear interpolation function: Lerp(from, to, amount), where amount is 0...1 which returns a value between from and to, by amount. How could I apply this same function to a rotational interpolation between 0 and 360 degrees? Given that degrees should not be returned outside 0 and 360.

Given this unit circle for degrees:

Unit Circle

where from = 45 and to = 315, the algorithm should take the shortest path to the angle, i.e. it should go through zero, to 360 and then to 315 - and not all the way round 90, 180, 270 to 315.

Is there a nice way to achieve this? Or is it going to just be a horrid mess of if() blocks? Am I missing some well understood standard way of doing this? Any help would be appreciated.

math rotation interpolation
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14

Sorry, that was a bit convoluted, here's a more concise version:

    public static float LerpDegrees(float start, float end, float amount)
    {
        float difference = Math.Abs(end - start);
        if (difference > 180)
        {
            // We need to add on to one of the values.
            if (end > start)
            {
                // We'll add it on to start...
                start += 360;
            }
            else
            {
                // Add it on to end.
                end += 360;
            }
        }

        // Interpolate it.
        float value = (start + ((end - start) * amount));

        // Wrap it..
        float rangeZero = 360;

        if (value >= 0 && value <= 360)
            return value;

        return (value % rangeZero);
    }

Anyone got a more optimised version?

answered 2010-04-25T15:29:49.493

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