Git commit 50e20cdcb3b01cb6107f20c1afed65967b27a767 by Stefan Gerlach.
Committed on 31/08/2016 at 20:39.
Pushed by sgerlach into branch 'master'.

small improvements on line simplification error calculation

M  +14   -4    src/backend/nsl/nsl_geom_linesim.c
M  +3    -3    src/backend/nsl/nsl_geom_linesim.h
M  +7    -7    src/backend/nsl/nsl_geom_linesim_test.c

http://commits.kde.org/labplot/50e20cdcb3b01cb6107f20c1afed65967b27a767

diff --git a/src/backend/nsl/nsl_geom_linesim.c b/src/backend/nsl/nsl_geom_=
linesim.c
index 3658c0e..68cedc3 100644
--- a/src/backend/nsl/nsl_geom_linesim.c
+++ b/src/backend/nsl/nsl_geom_linesim.c
@@ -26,27 +26,37 @@
  *                                                                        =
 *
  *************************************************************************=
**/
 =

+/*
+	TODO:
+	* struct of algorithm and names
+	* extern nsl_compare
+	* non-parametric functions (calculate eps from data)
+	* more algorithm
+	* error calculation by area
+	* error statistics
+*/
+
 #include <math.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include "nsl_geom.h"
 #include "nsl_geom_linesim.h"
 =

-double nsl_geom_linesim_positional_error(const double xdata[], const doubl=
e ydata[], const size_t n, const size_t index[]) {
+double nsl_geom_linesim_positional_squared_error(const double xdata[], con=
st double ydata[], const size_t n, const size_t index[]) {
 	double dist=3D0;
-	size_t i=3D0, j;	/* index of index[] */
+	size_t i=3D0, j;	/* i: index of index[] */
 	do {
 		/*for every point not in index[] calculate distance to line*/
 		/*printf("i=3D%d (index[i]-index[i+1]=3D%d-%d)\n", i , index[i], index[i=
+1]);*/
 		for(j=3D1;j<index[i+1]-index[i];j++) {
 			/*printf("i=3D%d: j=3D%d\n", i, j);*/
-			dist +=3D nsl_geom_point_line_dist(xdata[index[i]], ydata[index[i]], xd=
ata[index[i+1]], ydata[index[i+1]], xdata[index[i]+j], ydata[index[i]+j]);
+			dist +=3D pow(nsl_geom_point_line_dist(xdata[index[i]], ydata[index[i]]=
, xdata[index[i+1]], ydata[index[i+1]], xdata[index[i]+j], ydata[index[i]+j=
]), 2);
 			/*printf("dist =3D %g\n", dist);*/
 		}
 		i++;
 	} while(index[i] !=3D n-1);
 	=

-	return dist;
+	return dist/(double)n;
 }
 =

 size_t nsl_geom_linesim_nthpoint(const size_t n, const size_t step, size_t=
 index[]) {
diff --git a/src/backend/nsl/nsl_geom_linesim.h b/src/backend/nsl/nsl_geom_=
linesim.h
index d6d14ec..1b6ae54 100644
--- a/src/backend/nsl/nsl_geom_linesim.h
+++ b/src/backend/nsl/nsl_geom_linesim.h
@@ -31,10 +31,10 @@
 =

 #include <stdlib.h>
 =

-/* calculates positional error (summed perpendicular distance)
-	from simplified set (given by index[])
+/* calculates positional error (sum of squared perpendicular distance)
+	of simplified set (given by index[])
 */
-double nsl_geom_linesim_positional_error(const double xdata[], const doubl=
e ydata[], const size_t n, const size_t index[]);
+double nsl_geom_linesim_positional_squared_error(const double xdata[], con=
st double ydata[], const size_t n, const size_t index[]);
 =

 /* simple n-th point line simplification
 	n: number of points
diff --git a/src/backend/nsl/nsl_geom_linesim_test.c b/src/backend/nsl/nsl_=
geom_linesim_test.c
index 89c4fea..3701430 100644
--- a/src/backend/nsl/nsl_geom_linesim_test.c
+++ b/src/backend/nsl/nsl_geom_linesim_test.c
@@ -37,7 +37,7 @@ double main() {
 =

 	printf("* n-th point\n");
 	size_t nout =3D nsl_geom_linesim_nthpoint(n, np, index);
-	printf("nout =3D %d (error =3D %g)\n", nout, nsl_geom_linesim_positional_=
error(xdata, ydata, n, index));
+	printf("nout =3D %d (error =3D %g)\n", nout, nsl_geom_linesim_positional_=
squared_error(xdata, ydata, n, index));
 =

 	size_t i;
 	for(i=3D0; i<nout; i++)
@@ -46,7 +46,7 @@ double main() {
 	const double eps=3D1.5;
 	printf("* radial distance\n");
 	nout =3D nsl_geom_linesim_raddist(xdata, ydata, n, eps, index);
-	printf("nout =3D %d (error =3D %g)\n", nout, nsl_geom_linesim_positional_=
error(xdata, ydata, n, index));
+	printf("nout =3D %d (error =3D %g)\n", nout, nsl_geom_linesim_positional_=
squared_error(xdata, ydata, n, index));
 =

 	for(i=3D0; i<nout; i++)
 		printf("%d: %d\n", i, index[i]);
@@ -55,7 +55,7 @@ double main() {
 	const size_t repeat =3D 3;
 	printf("* perpendicular distance (repeat =3D %d)\n", repeat);
 	nout =3D nsl_geom_linesim_perpdist_repeat(xdata, ydata, n, eps2, repeat, =
index);
-	printf("nout =3D %d (error =3D %g)\n", nout, nsl_geom_linesim_positional_=
error(xdata, ydata, n, index));
+	printf("nout =3D %d (error =3D %g)\n", nout, nsl_geom_linesim_positional_=
squared_error(xdata, ydata, n, index));
 =

 	for(i=3D0; i<nout; i++)
 		printf("%d: %d\n", i, index[i]);
@@ -63,7 +63,7 @@ double main() {
 	const double eps3=3D0.7;
 	printf("* perp. distance (Reumann-Witkam)\n");
 	nout =3D nsl_geom_linesim_reumann_witkam(xdata, ydata, n, eps3, index);
-	printf("nout =3D %d (error =3D %g)\n", nout, nsl_geom_linesim_positional_=
error(xdata, ydata, n, index));
+	printf("nout =3D %d (error =3D %g)\n", nout, nsl_geom_linesim_positional_=
squared_error(xdata, ydata, n, index));
 =

 	for(i=3D0; i<nout; i++)
 		printf("%d: %d\n", i, index[i]);
@@ -72,7 +72,7 @@ double main() {
 	const double maxeps=3D7.0;
 	printf("* perp. distance (Opheim)\n");
 	nout =3D nsl_geom_linesim_opheim(xdata, ydata, n, mineps, maxeps, index);
-	printf("nout =3D %d (error =3D %g)\n", nout, nsl_geom_linesim_positional_=
error(xdata, ydata, n, index));
+	printf("nout =3D %d (error =3D %g)\n", nout, nsl_geom_linesim_positional_=
squared_error(xdata, ydata, n, index));
 =

 	for(i=3D0; i<nout; i++)
 		printf("%d: %d\n", i, index[i]);
@@ -81,7 +81,7 @@ double main() {
 	const size_t region=3D5;
 	printf("* simplification (Lang)\n");
 	nout =3D nsl_geom_linesim_lang(xdata, ydata, n, eps4, region, index);
-	printf("nout =3D %d (error =3D %g)\n", nout, nsl_geom_linesim_positional_=
error(xdata, ydata, n, index));
+	printf("nout =3D %d (error =3D %g)\n", nout, nsl_geom_linesim_positional_=
squared_error(xdata, ydata, n, index));
 =

 	for(i=3D0; i<nout; i++)
 		printf("%d: %d\n", i, index[i]);
@@ -89,7 +89,7 @@ double main() {
 	const double eps5=3D0.6;
 	printf("* simplification (Douglas Peucker)\n");
 	nout =3D nsl_geom_linesim_douglas_peucker(xdata, ydata, n, eps5, index);
-	printf("nout =3D %d (error =3D %g)\n", nout, nsl_geom_linesim_positional_=
error(xdata, ydata, n, index));
+	printf("nout =3D %d (error =3D %g)\n", nout, nsl_geom_linesim_positional_=
squared_error(xdata, ydata, n, index));
 =

 	for(i=3D0; i<nout; i++)
 		printf("%d: %d\n", i, index[i]);