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copied!<p>The problem is probably due to crossing the 360 degrees / 0 degrees boundary.</p> <p>Using h = heading i.e. the direction the missile is travelling in, and t = the direction from the missile to the target and f=0.1. Now consider the situation where t is 20 degrees clockwise to h. </p> <p>If h = 180 then t = 200 and h(final) = 0.9*180+0.1*200 = 182, so the missile has turned a small amount clockwise as expected.</p> <p>But if h = 350 then t = 370 = 10 (according to the atan formula), so now h(final) = 0.9*350+0.1*10=316 and the missile has turned a large distance in the wrong direction. </p> <p>You need to add a little logic to check for the zero crossing and avoid this problem.</p> <p><strong>Added comment</strong> </p> <p>OK - atan is always a tricky thing, as b = tan(a) is valid for any a in the range (-inf < a < + inf), but a = atan(b) will always provide a b in some range (bmin <= b < bmin + 360), so as a vector rotates around in a circle, at some point there will be a discontinuity in the calculated angle as it rises past bmin + 360 and immediately drops to bmin or as it falls below bmin and suddenly jumps up to bmin + 360. If I am not making myself clear, then just consider what happens when a clock goes past 12:59 pm. It doesn't continue on to 13:00 (except in Europe), but instead drops back to 1:00 am.</p> <p>Blackbear's answer shows the correct idea. My equivalent 'fix' would be to replace your line</p> <pre><code> heading = (1 - f) * oldHeading + f * Math.atan2(atanY, atanX); </code></pre> <p>with something like</p> <pre><code> TheAngle = Math.atan2(atanY, atanX); if Abs(TheAngle-oldheading) > 180 then TheAngle = TheAngle - Sign(TheAngle)*360; heading = (1 - f) * oldHeading + f * TheAngle; </code></pre> <p>where Sign(x) = +1 for x >=0 and -1 for x < 0</p> <p>Note that my code is not quite in C++, Java, or whatever you are using, so you won't be able to do a direct cut-and-paste - but you should be able to translate it into something useful.</p>

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