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authorAndré Nusser <andre.nusser@googlemail.com>2020-04-25 22:45:47 +0200
committerAndré Nusser <andre.nusser@googlemail.com>2020-04-25 22:46:10 +0200
commit8d22262afd0f91b49cb046d090b186c4305d470b (patch)
tree33977ef13d978f16b3b19ddab529145854255b4e /src
parent75be125fb0f50a8e4e766ca70f15b5822c0076e2 (diff)
Introduce Steffen monotone cubic splines.
Diffstat (limited to 'src')
-rw-r--r--src/powermap.cc65
-rw-r--r--src/powermap.h6
2 files changed, 56 insertions, 15 deletions
diff --git a/src/powermap.cc b/src/powermap.cc
index 2dd5df4..ca17a60 100644
--- a/src/powermap.cc
+++ b/src/powermap.cc
@@ -156,18 +156,43 @@ void Powermap::updateSpline()
assert(0. <= fixed[0].out && fixed[0].out <= fixed[1].out &&
fixed[1].out <= fixed[2].out && fixed[2].out <= 1.);
- // TODO: What to do if fixed[0] is (0,0) or fixed[2] is (1,1)??
Powers X = shelf ? Powers{fixed[0].in, fixed[1].in, fixed[2].in}
: Powers{0., fixed[0].in, fixed[1].in, fixed[2].in, 1.};
- Powers P = shelf ? Powers{fixed[0].out, fixed[1].out, fixed[2].out}
+ Powers Y = shelf ? Powers{fixed[0].out, fixed[1].out, fixed[2].out}
: Powers{0., fixed[0].out, fixed[1].out, fixed[2].out, 1.};
+ auto slopes = calcSlopes(X, Y);
+
+ if (shelf) {
+ assert(slopes.size() == 3);
+ this->m[1] = slopes[0];
+ this->m[2] = slopes[1];
+ this->m[3] = slopes[2];
+ }
+ else {
+ assert(slopes.size() == 5);
+ for (std::size_t i = 0; i < m.size(); ++i) {
+ this->m[i] = slopes[i];
+ }
+ }
+
+ spline_needs_update = false;
+}
+
+std::vector<float> Powermap::calcSlopes(Powers const& X, Powers const& Y)
+{
+ // return calcSlopesFritschCarlson(X, Y);
+ return calcSlopesSteffen(X, Y);
+}
+
+std::vector<float> Powermap::calcSlopesFritschCarlson(Powers const& X, Powers const& Y)
+{
Powers deltas(X.size()-1);
Powers m(X.size());
// 1
for (std::size_t i = 0; i < deltas.size(); ++i) {
- deltas[i] = (P[i+1]-P[i])/(X[i+1]-X[i]);
+ deltas[i] = (Y[i+1]-Y[i])/(X[i+1]-X[i]);
}
// 2
@@ -227,20 +252,32 @@ void Powermap::updateSpline()
}
}
- if (shelf) {
- assert(m.size() == 3);
- this->m[1] = m[0];
- this->m[2] = m[1];
- this->m[3] = m[2];
+ return m;
+}
+
+std::vector<float> Powermap::calcSlopesSteffen(Powers const& X, Powers const& Y)
+{
+ Powers m(X.size());
+
+ Powers d(X.size()-1);
+ Powers h(X.size()-1);
+ for (std::size_t i = 0; i < d.size(); ++i) {
+ h[i] = X[i+1]-X[i];
+ d[i] = (Y[i+1]-Y[i])/h[i];
}
- else {
- assert(m.size() == 5);
- for (std::size_t i = 0; i < m.size(); ++i) {
- this->m[i] = m[i];
- }
+
+ m.front() = d.front();
+ for (std::size_t i = 1; i < m.size()-1; ++i) {
+ m[i] = (d[i-1] + d[i])/2.;
}
+ m.back() = d.back();
- spline_needs_update = false;
+ for (std::size_t i = 1; i < m.size()-1; ++i) {
+ auto const min_d = 2*std::min(d[i-1], d[i]);
+ m[i] = std::min<float>(min_d, (h[i]*d[i-1] + h[i-1]*d[i])/(h[i-1]+h[i]));
+ }
+
+ return m;
}
Power Powermap::clamp(Power in, Power min, Power max) const
diff --git a/src/powermap.h b/src/powermap.h
index 29a3c81..b942722 100644
--- a/src/powermap.h
+++ b/src/powermap.h
@@ -64,9 +64,13 @@ private:
// spline parameters (deterministically computed from the input parameters)
std::array<float, 5> m;
-
bool spline_needs_update;
+
void updateSpline();
+ std::vector<float> calcSlopes(Powers const& X, Powers const& P);
+ std::vector<float> calcSlopesFritschCarlson(Powers const& X, Powers const& P);
+ std::vector<float> calcSlopesSteffen(Powers const& X, Powers const& P);
+
Power clamp(Power in, Power min, Power max) const;
const Power eps = 1e-3;