re: crv.evaluateCurvature, here is some test code. Make a curve, select it and then push the Tab key and paste this in to the XYZ input control:

var crv = moi.geometryDatabase.getSelectedObjects().getCurves().item(0);
var pt = crv.evaluatePoint( crv.domainMin );
var K = crv.evaluateCurvature( crv.domainMin );
var f = moi.command.createFactory( 'line' );
f.setInput( 0, pt );
f.setInput( 1, moi.vectorMath.add( pt, K ) );
f.commit();

That will make a line showing the curvature vector. The radius of curvature is 1 / length of that line.

Curvature vectors are generally scaled up by quite a bit when used for visualization purposes. They tend to be small in their direct form.

- Michael