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Refactoring of curve fitting algorithm:

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removal of artificial extension at the ends of the curve
removal of observation points normalization
added clamping of parameter index which compensates for under-represented spline segments
added parameter for level of freedom at the ends of the curve
This commit is contained in:
PavelMikus 2022-04-01 15:50:51 +02:00
parent c19770189f
commit 396d3215bd
4 changed files with 68 additions and 93 deletions
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6
src/libslic3r/GCode/SeamPlacer.cpp
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@ -1199,9 +1199,9 @@ void SeamPlacer::align_seam_points(const PrintObject *po, const SeamPlacerImpl::
}
// Curve Fitting
size_t number_of_splines = std::max(size_t(1),
size_t(observations.size() / SeamPlacer::seam_align_seams_per_spline));
auto curve = Geometry::fit_cubic_bspline(observations, observation_points, weights, number_of_splines);
size_t number_of_segments = std::max(size_t(1),
size_t(observations.size() / SeamPlacer::seam_align_seams_per_segment));
auto curve = Geometry::fit_cubic_bspline(observations, observation_points, weights, number_of_segments);
// Do alignment - compute fitted point for each point in the string from its Z coord, and store the position into
// Perimeter structure of the point; also set flag aligned to true

2
src/libslic3r/GCode/SeamPlacer.hpp
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@ -118,7 +118,7 @@ public:
// minimum number of seams needed in cluster to make alignemnt happen
static constexpr size_t seam_align_minimum_string_seams = 6;
// points covered by spline; determines number of splines for the given string
static constexpr size_t seam_align_seams_per_spline = 30;
static constexpr size_t seam_align_seams_per_segment = 8;
//The following data structures hold all perimeter points for all PrintObject. The structure is as follows:
// Map of PrintObjects (PO) -> vector of layers of PO -> vector of perimeter points of the given layer

149
src/libslic3r/Geometry/Curves.hpp
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@ -6,6 +6,8 @@
#include <iostream>
//#define LSQR_DEBUG
namespace Slic3r {
namespace Geometry {
@ -53,7 +55,7 @@ PolynomialCurve<Dimension, NumberType> fit_polynomial(const std::vector<Vec<Dime
coefficients.row(dim) = QR.solve(data_points.row(dim).transpose());
}
return { std::move(coefficients) };
return {std::move(coefficients)};
}
template<size_t Dimension, typename NumberType, typename KernelType>
@ -62,33 +64,24 @@ struct PiecewiseFittedCurve {
Eigen::MatrixXf coefficients;
NumberType start;
NumberType length;
NumberType n_segment_size;
size_t segments() const { return this->coefficients.cols(); }
NumberType get_n_segment_start(int segment_index) const {
return n_segment_size * segment_index;
}
NumberType normalize(const NumberType &observation_point) const {
return (observation_point - start) / length;
}
NumberType segment_size;
size_t endpoints_level_of_freedom;
Vec<Dimension, NumberType> get_fitted_value(const NumberType &observation_point) const {
Vec<Dimension, NumberType> result = Vec<Dimension, NumberType>::Zero();
NumberType t = normalize(observation_point);
int start_segment_idx = int(floor(t / this->n_segment_size)) - int(Kernel::kernel_span * 0.5f - 1.0f);
//find corresponding segment index; expects kernels to be centered; NOTE: shift by number of additional segments, which are outside of the valid length
int middle_right_segment_index = floor((observation_point - start) / segment_size);
//find index of first segment that is affected by the point i; this can be deduced from kernel_span
int start_segment_idx = middle_right_segment_index - Kernel::kernel_span / 2 + 1;
for (int segment_index = start_segment_idx; segment_index < int(start_segment_idx + Kernel::kernel_span);
segment_index++) {
if (segment_index < 0 || segment_index >= int(this->coefficients.cols())) {
continue;
}
NumberType segment_start = this->get_n_segment_start(segment_index);
NumberType normalized_segment_distance = (segment_start - t) / this->n_segment_size;
NumberType segment_start = start + segment_index * segment_size;
NumberType normalized_segment_distance = (segment_start - observation_point) / segment_size;
result += Kernel::kernel(normalized_segment_distance) * coefficients.col(segment_index);
int parameter_index = segment_index + endpoints_level_of_freedom;
parameter_index = std::clamp(parameter_index, 0, int(coefficients.cols()) - 1);
result += Kernel::kernel(normalized_segment_distance) * coefficients.col(parameter_index);
}
return result;
}
@ -106,99 +99,77 @@ PiecewiseFittedCurve<Dimension, NumberType, Kernel> fit_curve(
const std::vector<Vec<Dimension, NumberType>> &observations,
const std::vector<NumberType> &observation_points,
const std::vector<NumberType> &weights,
size_t number_of_inner_splines) {
size_t segments_count,
size_t endpoints_level_of_freedom) {
// check to make sure inputs are correct
assert(number_of_inner_splines >= 1);
assert(segments_count > 0);
assert(observations.size() > 0);
assert(observation_points.size() == observations.size());
assert(observation_points.size() == weights.size());
assert(number_of_inner_splines <= observations.size());
assert(observations.size() >= 4);
size_t extremes_repetition = Kernel::kernel_span - 1; //how many (additional) times is the first and last point repeated
assert(segments_count <= observations.size());
//prepare sqrt of weights, which will then be applied to both matrix T and observed data: https://en.wikipedia.org/wiki/Weighted_least_squares
std::vector<NumberType> sqrt_weights(weights.size() + extremes_repetition * 2);
std::vector<NumberType> sqrt_weights(weights.size());
for (size_t index = 0; index < weights.size(); ++index) {
assert(weights[index] > 0);
sqrt_weights[index + extremes_repetition] = sqrt(weights[index]);
}
//repeat weights for addtional extreme segments
{
auto first = sqrt_weights[extremes_repetition];
auto last = sqrt_weights[extremes_repetition + weights.size() - 1];
for (int index = 0; index < int(extremes_repetition); ++index) {
sqrt_weights[index] = first;
sqrt_weights[sqrt_weights.size() - index - 1] = last;
}
sqrt_weights[index] = sqrt(weights[index]);
}
// prepare result and compute metadata
PiecewiseFittedCurve<Dimension, NumberType, Kernel> result { };
NumberType orig_len = observation_points.back() - observation_points.front();
NumberType orig_segment_size = orig_len / NumberType(number_of_inner_splines * Kernel::kernel_span);
result.start = observation_points.front() - extremes_repetition * orig_segment_size;
result.length = observation_points.back() + extremes_repetition * orig_segment_size - result.start;
size_t segments_count = number_of_inner_splines * Kernel::kernel_span + extremes_repetition * 2;
result.n_segment_size = NumberType(1) / NumberType(segments_count - 1);
//normalize observations points by start and length
std::vector<NumberType> normalized_obs_points(observation_points.size() + extremes_repetition * 2);
for (size_t index = 0; index < observation_points.size(); ++index) {
normalized_obs_points[index + extremes_repetition] = result.normalize(observation_points[index]);
}
// create artificial values at the extremes for constant curve fitting
for (int index = 0; index < int(extremes_repetition); ++index) {
normalized_obs_points[extremes_repetition - 1 - index] = result.normalize(observation_points.front()
- index * orig_segment_size - NumberType(0.5) * orig_segment_size);
normalized_obs_points[normalized_obs_points.size() - extremes_repetition + index] = result.normalize(
observation_points.back() + index * orig_segment_size + NumberType(0.5) * orig_segment_size);
}
NumberType valid_length = observation_points.back() - observation_points.front();
NumberType segment_size = valid_length / NumberType(segments_count);
result.start = observation_points.front();
result.segment_size = segment_size;
result.endpoints_level_of_freedom = endpoints_level_of_freedom;
// prepare observed data
// Eigen defaults to column major memory layout.
Eigen::MatrixXf data_points(Dimension, observations.size() + extremes_repetition * 2);
for (size_t index = 0; index < observations.size(); ++ index) {
data_points.col(index + extremes_repetition) = observations[index]
* sqrt_weights[index + extremes_repetition];
}
//duplicate observed data at the extremes
for (int index = 0; index < int(extremes_repetition); index++) {
data_points.col(index) = observations.front() * sqrt_weights[index];
data_points.col(data_points.cols() - index - 1) = observations.back()
* sqrt_weights[data_points.cols() - index - 1];
Eigen::MatrixXf data_points(Dimension, observations.size());
for (size_t index = 0; index < observations.size(); ++index) {
data_points.col(index) = observations[index] * sqrt_weights[index];
}
size_t parameters_count = segments_count + 1 + 2 * endpoints_level_of_freedom;
//Create weight matrix T for each point and each segment;
Eigen::MatrixXf T(normalized_obs_points.size(), segments_count);
Eigen::MatrixXf T(observation_points.size(), parameters_count);
T.setZero();
//Fill the weight matrix
for (size_t i = 0; i < normalized_obs_points.size(); ++i) {
NumberType knot_val = normalized_obs_points[i];
for (size_t i = 0; i < observation_points.size(); ++i) {
NumberType observation_point = observation_points[i];
//find corresponding segment index; expects kernels to be centered
int middle_right_segment_index = floor((observation_point - result.start) / result.segment_size);
//find index of first segment that is affected by the point i; this can be deduced from kernel_span
int start_segment_idx = int(floor(knot_val / result.n_segment_size)) - int(Kernel::kernel_span * 0.5f - 1.0f);
int start_segment_idx = middle_right_segment_index - Kernel::kernel_span / 2 + 1;
for (int segment_index = start_segment_idx; segment_index < int(start_segment_idx + Kernel::kernel_span);
segment_index++) {
// skip if we overshoot segment_index - happens at the extremes
if (segment_index < 0 || segment_index >= int(segments_count)) {
continue;
}
NumberType segment_start = result.get_n_segment_start(segment_index);
NumberType normalized_segment_distance = (segment_start - knot_val) / result.n_segment_size;
// fill in kernel value with weight applied
NumberType segment_start = result.start + segment_index * result.segment_size;
NumberType normalized_segment_distance = (segment_start - observation_point) / result.segment_size;
T(i, segment_index) += Kernel::kernel(normalized_segment_distance) * sqrt_weights[i];
int parameter_index = segment_index + endpoints_level_of_freedom;
parameter_index = std::clamp(parameter_index, 0, int(parameters_count) - 1);
T(i, parameter_index) += Kernel::kernel(normalized_segment_distance) * sqrt_weights[i];
}
}
#ifdef LSQR_DEBUG
std::cout << "weight matrix: " << std::endl;
for (int obs = 0; obs < observation_points.size(); ++obs) {
std::cout << std::endl;
for (int segment = 0; segment < parameters_count; ++segment) {
std::cout << T(obs, segment) << " ";
}
}
std::cout << std::endl;
#endif
// Solve for linear least square fit
result.coefficients.resize(Dimension, segments_count);
result.coefficients.resize(Dimension, parameters_count);
const auto QR = T.fullPivHouseholderQr();
for (size_t dim = 0; dim < Dimension; ++dim) {
result.coefficients.row(dim) = QR.solve(data_points.row(dim).transpose());
result.coefficients.row(dim) = QR.solve(data_points.row(dim).transpose());
}
return result;
@ -210,8 +181,10 @@ fit_cubic_bspline(
const std::vector<Vec<Dimension, NumberType>> &observations,
std::vector<NumberType> observation_points,
std::vector<NumberType> weights,
size_t number_of_segments) {
return fit_curve<CubicBSplineKernel<NumberType>>(observations, observation_points, weights, number_of_segments);
size_t segments_count,
size_t endpoints_level_of_freedom = 0) {
return fit_curve<CubicBSplineKernel<NumberType>>(observations, observation_points, weights, segments_count,
endpoints_level_of_freedom);
}
template<int Dimension, typename NumberType>
@ -220,8 +193,10 @@ fit_catmul_rom_spline(
const std::vector<Vec<Dimension, NumberType>> &observations,
std::vector<NumberType> observation_points,
std::vector<NumberType> weights,
size_t number_of_segments) {
return fit_curveCubicCatmulRomKernel<NumberType>(observations, observation_points, weights, number_of_segments);
size_t segments_count,
size_t endpoints_level_of_freedom = 0) {
return fit_curve<CubicCatmulRomKernel<NumberType>>(observations, observation_points, weights, segments_count,
endpoints_level_of_freedom);
}
}

4
src/libslic3r/Point.hpp
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@ -104,8 +104,8 @@ template<typename Derived, typename Derived2>
inline double angle(const Eigen::MatrixBase<Derived> &v1, const Eigen::MatrixBase<Derived2> &v2) {
static_assert(Derived::IsVectorAtCompileTime && int(Derived::SizeAtCompileTime) == 2, "angle(): first parameter is not a 2D vector");
static_assert(Derived2::IsVectorAtCompileTime && int(Derived2::SizeAtCompileTime) == 2, "angle(): second parameter is not a 2D vector");
auto v1d = v1.typename cast<double>();
auto v2d = v2.typename cast<double>();
auto v1d = v1.template cast<double>();
auto v2d = v2.template cast<double>();
return atan2(cross2(v1d, v2d), v1d.dot(v2d));
}