[GRASS-user] circle surrounding neighbors

[Glynn Clements]

bks at centrum.cz wrote:

> don't you know about any possibility to use something similar to r.neighbors
> but  for the circle surrounding of the pixel?

Modify raster/r.neighbors/gather.c.

An (untested) attempt is attached.

-- 
Glynn Clements <glynn at gclements.plus.com>

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#include <grass/gis.h>
#include "ncb.h"

/*
   given the starting col of the neighborhood,
   copy the cell values from the bufs into the array of values
   and return the number of values copied.
*/

static char **mask;

static void init_mask(void)
{
    int i, j;

    if (mask)
	return;

    mask = G_malloc(ncb.nsize * sizeof(char *));

    for (i = 0; i < ncb.nsize; i++)
	mask[i] = G_malloc(ncb.nsize);

    for (i = 0; i < ncb.nsize; i++)
	for (j = 0; j < ncb.nsize; j++)
	    mask[i][j] = sqr(i - ncb.dist) + sqr(j - ncb.dist) <= sqr(ncb.dist);
}

int gather(DCELL *values, int offset)
{
    int row, col;
    int n = 0;

    *values = 0;

    if (!mask)
	init_mask();

    for (row = 0; row < ncb.nsize; row++)
	for (col = 0; col < ncb.nsize; col++)
	{
	    DCELL *c = &ncb.buf[row][offset + col];

	    if (!mask[row][col])
		continue;

	    if (G_is_d_null_value(c))
		G_set_d_null_value(&values[n], 1);
	    else
		values[n] = *c;

	    n++;
	}

    return n ? n : -1;
}