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-rw-r--r--digital/avr/modules/math/geometry/distance.c71
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diff --git a/digital/avr/modules/math/geometry/distance.c b/digital/avr/modules/math/geometry/distance.c
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+/* distance.c */
+/* avr.math.geometry - Geometry math module. {{{
+ *
+ * Copyright (C) 2010 Nicolas Schodet
+ *
+ * APBTeam:
+ * Web: http://apbteam.org/
+ * Email: team AT apbteam DOT org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * }}} */
+#include "common.h"
+#include "distance.h"
+
+#include "modules/utils/utils.h"
+
+int16_t
+distance_segment_point (vect_t *a, vect_t *b, vect_t *p)
+{
+ int16_t proj;
+ /* The space is split in three regions delimited by the two parallel lines
+ * going through A and B, perpendicular to the segment:
+ *
+ * | |
+ * | 2 |
+ * | |
+ * 1 A=======B 3
+ * | |
+ * | 2 |
+ * | |
+ *
+ * If P is in region 2, distance is the distance between P and the AB
+ * line.
+ *
+ * If P is in region 1, distance is |AP|. If P is in region 3, distance
+ * is |BP|.
+ *
+ * If vAP . vAB <= 0, P is in region 1. If vBP . vAB > 0, P is in region
+ * 3. Else, it is in region 2.
+ *
+ * Distance to line is determined using dot product between vn, a normal
+ * of vAB and vBP. */
+ vect_t vab, vap, vbp;
+ /* Region 1? */
+ vab = *b; vect_sub (&vab, a);
+ vap = *p; vect_sub (&vap, a);
+ if (vect_dot_product (&vab, &vap) <= 0)
+ return vect_norm (&vap);
+ /* Region 3? */
+ vbp = *p; vect_sub (&vbp, b);
+ if (vect_dot_product (&vab, &vbp) > 0)
+ return vect_norm (&vbp);
+ /* Else, region 2. */
+ vect_normal (&vab);
+ proj = vect_dot_product (&vab, &vbp) / vect_norm (&vab);
+ return UTILS_ABS (proj);
+}
+