vicrucann/curvefitting

:wavy_dash: Curve fitting based on Schneider's algorithm. Written using C++11 and OpenSceneGraph (visualization)

curvefitting's Issues

Test of exponential sensitivity

This is James Phillips, author of the Python language pyeq3 curve fitting library on GitHub at https://github.com/zunzun/pyeq3. I include in my code's unit tests a test of exponential sensitivity that you might be interested in, the equation to be fitted is

y = a * exp(bx) + Offset

and the data for the test is

x y
0.9 -2997.81165143259
1.5 -2997.67633151454
13.8 -2992.05019674501
19.8 -2985.51451402968
24.1 -2977.73207770987
28.2 -2966.44629865572
35.2 -2932.4311430723
60.3 -2168.56994123603
74.6 474.296114697706
81.3 3789.59913028271

Fitted coefficients should be

a = 2.0
b = 0.1
Offset = -3000.0

The test is quite sensitive. My nonlinear fitter uses the Differential Evolution genetic algorithm to determine initial parameters for the Levenberg-Marquardt nonlinear fitter in scipy's Python fitter.

James

`handle1` and `handle2` in `generateBezier()` should be instantiated with `getNANPoint()`

I realize this repo has been untouched for many years and I don't know if PRs are welcome but I think this is a small bug with an easy fix. In the function generateBezier(), two Point2 variables are instantiated with their default constructor. The following block of code may or may not modify them. Then they are tested for "NaN-ness" with isNaN(). If the Point2's default constructor does not initialize the point's coordinates with NAN, I believe this test will sometimes fail when it should succeed.

It's my understanding that the code expects Point2 to default initialize to NaN when that may not always be the case. It is indeed not the case for osg::Vec3f which default initializes to all 0.

Easy fix. This line:
Point2 handle1, handle2;

should be:

Point2 handle1 = this->getNANPoint(), handle2 = this->getNANPoint();

I've observed the effect of this bug with a sawtooth path and the first two segments of the resulting curve had control points P1 and P2 equal to P0 and P3 respectively.

Bad:

Fixed:

That second screenshot is also what one can observe with paper.js