# Approximate Bezier Curve Length

Hi,
We’re now in the final stages of product completion and need to address a couple of minor tweaks. We use bezier curves to define many of our object trajectories … but we use linear interpolation based on the origin to destination … and for 95% of the time the effect is fine. However for short ‘as the crow flies’ trajectories, there is a significant difference between the actual curve distance.

Is there a way in which we could derive an very rough approximation of the bezier path length ?

Whilst our maths isn’t too bad … we’d appreciate responses that are more practical and maybe not those from the academic world !

We use a bezier definition of StartPoint, ControlPoint1, ControlPoint2 and EndPoint - all defined as Vectors.

Many thanks

Andrew

i don’t know of any “rough approximations” to the arc length of a bezier curve, but you could just use the standard integration method. go here , and take a look at the pdfs titled “moving at constant speed” and “numerical integration”.

Many thanks for the link … if nothing else I’ve now got a lot of reading to do … there’s some really good information here.

With regard to my original problem, I came up with something that works OK for my case …

function BezierLength : GLfloat;
// Rough approximation for the bezier path length.
var
LinearLength : GLfloat;
begin
with fBezier do begin
LinearLength := VectorLength(VectorSubtract(StartPoint, EndPoint));
Result := (VectorLength(VectorSubtract(StartPoint, ControlPoint1)) +
VectorLength(VectorSubtract(EndPoint, ControlPoint2))) / 1.5;
if (Result < LinearLength) then
Result := LinearLength;
end; {with}
end; {BezierLength}

Andrew

[This message has been edited by Andrew Jameson (edited 04-27-2003).]