v.kernel: stddeviation -> radius

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@54271 15284696-431f-4ddb-bdfa-cd5b030d7da7

vector/v.kernel/function.c

@@ -103,9 +103,10 @@ double euclidean_distance(double *x, double *y, int n)
 
 /*****************kernel density functions******************************/
 
-double gaussianKernel2(double term, double bandwidth, double x)
+double gaussianKernel4(double term, double bandwidth, double x)
 {
     /* term is set by setKernelFunction */
+    /* bandwidth is here SD */
 
     /*
     double term =
@@ -114,7 +115,8 @@ double gaussianKernel2(double term, double bandwidth, double x)
 
     x /= bandwidth;
 
-    return (term * exp(-(x * x) / 2.));
+    /* SD = radius (bandwidth) / 4 */
+    return (term * exp((x * x) / -2.));
 }
 
 /* Note: these functions support currently only 1D and 2D, consider this for example 
@@ -290,7 +292,7 @@ void setKernelFunction(int function, int dimension, double bandwidth, double *te
 	*term *= (35. / 32);
 	break;
     case KERNEL_GAUSSIAN:
-	kernelfn = gaussianKernel2;
+	kernelfn = gaussianKernel4;
 	*term =
 	    1. / (pow(bandwidth, dimension) * pow((2. * M_PI), dimension / 2.));
 	break;

vector/v.kernel/main.c

@@ -75,7 +75,7 @@ double L(double smooth)
 int main(int argc, char **argv)
 {
     struct Option *in_opt, *net_opt, *out_opt;
-    struct Option *stddev_opt, *dsize_opt, *segmax_opt, *netmax_opt,
+    struct Option *radius_opt, *dsize_opt, *segmax_opt, *netmax_opt,
 	*multip_opt, *node_opt, *kernel_opt;
     struct Flag *flag_o, *flag_q, *flag_normalize, *flag_multiply;
     char *desc;
@@ -125,11 +125,11 @@ int main(int argc, char **argv)
     out_opt->required = YES;
     out_opt->description = _("Output raster/vector map");
 
-    stddev_opt = G_define_option();
-    stddev_opt->key = "stddeviation";
-    stddev_opt->type = TYPE_DOUBLE;
-    stddev_opt->required = YES;
-    stddev_opt->description = _("Standard deviation in map units");
+    radius_opt = G_define_option();
+    radius_opt->key = "radius";
+    radius_opt->type = TYPE_DOUBLE;
+    radius_opt->required = YES;
+    radius_opt->description = _("Kernel radius in map units");
 
     dsize_opt = G_define_option();
     dsize_opt->key = "dsize";
@@ -206,7 +206,8 @@ int main(int argc, char **argv)
 	exit(EXIT_FAILURE);
 
     /*read options */
-    sigma = atof(stddev_opt->answer);
+    dmax = atof(radius_opt->answer);
+    sigma = dmax;
     dsize = atof(dsize_opt->answer);
     segmax = atof(segmax_opt->answer);
     netmax = atof(netmax_opt->answer);
@@ -374,9 +375,8 @@ int main(int argc, char **argv)
 	}
     }
 
-    dmax = sigma;
     if (kernel_function == KERNEL_GAUSSIAN)
-	dmax = sigma * 4.;  /* should be sigma /= 4.; */
+	sigma /= 4.;
 
     if (net_opt->answer) {
 	setKernelFunction(kernel_function, 1, sigma, &term);

vector/v.kernel/v.kernel.html

@@ -16,7 +16,12 @@ and can be enabled with <em>node=split</em>.
 The <em>mult</em> option is needed to overcome the limitation that
 the resulting density in case of a vector map output is stored as category
 (Integer). The density result stored as category may be multiplied by this number.
-<p>With the <em>-o</em> flag (experimental) the command tries to calculate an 
+<p>
+For the <em>gaussian</em> kernel, standard deviation for the 
+<a href="http://en.wikipedia.org/wiki/Kernel_(statistics)#Kernel_functions_in_common_use">gaussian function</a> 
+is set to 1/4 of the radius.
+<p>
+With the <em>-o</em> flag (experimental) the command tries to calculate an 
 optimal standard deviation. The value of <em>stddeviation</em> is taken 
 as maximum value. Standard deviation is calculated using ALL points, 
 not just those in the current region.