[GRASS-SVN] r54419 - grass/trunk/raster/r.drain
svn_grass at osgeo.org
svn_grass at osgeo.org
Thu Dec 27 08:06:59 PST 2012
Author: mmetz
Date: 2012-12-27 08:06:59 -0800 (Thu, 27 Dec 2012)
New Revision: 54419
Modified:
grass/trunk/raster/r.drain/main.c
grass/trunk/raster/r.drain/r.drain.html
Log:
r.drain: use standard GRASS directions, update manual
Modified: grass/trunk/raster/r.drain/main.c
===================================================================
--- grass/trunk/raster/r.drain/main.c 2012-12-27 16:06:21 UTC (rev 54418)
+++ grass/trunk/raster/r.drain/main.c 2012-12-27 16:06:59 UTC (rev 54419)
@@ -682,70 +682,70 @@
G_message(_("direction read: %lf, neighbour found: %i"),
direction, neighbour);
switch (neighbour) {
- case 1800:
- next_row = list->row;
+ case 225: /* ENE */
+ next_row = list->row - 1;
+ next_col = list->col + 2;
+ break;
+ case 450: /* NE */
+ next_row = list->row - 1;
next_col = list->col + 1;
break;
- case 0:
- next_row = list->row;
- next_col = list->col - 1;
+ case 675: /* NNE */
+ next_row = list->row - 2;
+ next_col = list->col + 1;
break;
- case 900:
- next_row = list->row + 1;
- next_col = list->col;
- break;
- case 2700:
+ case 900: /* N */
next_row = list->row - 1;
next_col = list->col;
break;
- case 1350:
- next_col = list->col + 1;
- next_row = list->row + 1;
+ case 1125: /* NNW */
+ next_row = list->row - 2;
+ next_col = list->col - 1;
break;
- case 450:
+ case 1350: /* NW */
next_col = list->col - 1;
- next_row = list->row + 1;
+ next_row = list->row - 1;
break;
- case 3150:
+ case 1575: /* WNW */
+ next_col = list->col - 2;
next_row = list->row - 1;
+ break;
+ case 1800: /* W*/
+ next_row = list->row;
next_col = list->col - 1;
break;
- case 2250:
- next_row = list->row - 1;
- next_col = list->col + 1;
+ case 2025: /* WSW */
+ next_row = list->row + 1;
+ next_col = list->col - 2;
break;
- case 1125:
- next_row = list->row + 2;
- next_col = list->col + 1;
+ case 2250: /* SW */
+ next_row = list->row + 1;
+ next_col = list->col - 1;
break;
- case 675:
+ case 2475: /* SSW */
next_row = list->row + 2;
next_col = list->col - 1;
break;
- case 2925:
- next_row = list->row - 2;
- next_col = list->col - 1;
+ case 2700: /* S */
+ next_row = list->row + 1;
+ next_col = list->col;
break;
- case 2475:
- next_row = list->row - 2;
+ case 2925: /* SSE */
+ next_row = list->row + 2;
next_col = list->col + 1;
break;
- case 1575:
+ case 3150: /* SE */
next_row = list->row + 1;
- next_col = list->col + 2;
+ next_col = list->col + 1;
break;
- case 225:
+ case 3375: /* ESE */
next_row = list->row + 1;
- next_col = list->col - 2;
+ next_col = list->col + 2;
break;
- case 3375:
- next_row = list->row - 1;
- next_col = list->col - 2;
+ case 3600: /* E */
+ next_row = list->row;
+ next_col = list->col + 1;
break;
- case 2025:
- next_row = list->row - 1;
- next_col = list->col + 2;
- break;
/* default:
break;
Should probably add something here for the possibility of a non-direction map
Modified: grass/trunk/raster/r.drain/r.drain.html
===================================================================
--- grass/trunk/raster/r.drain/r.drain.html 2012-12-27 16:06:21 UTC (rev 54418)
+++ grass/trunk/raster/r.drain/r.drain.html 2012-12-27 16:06:59 UTC (rev 54419)
@@ -1,10 +1,13 @@
<h2>DESCRIPTION</h2>
<em>r.drain</em> traces a flow through a least-cost path in an elevation
-model. If the <b>input</b> surface (a raster map layer) is a cumulative
-cost map generated by the <em><a href="r.walk.html">r.walk</a></em> or
-<em><a href="r.cost.html">r.cost</a></em> modules, the -d flag and a
-movement direction surface <b>"indir"</b> must be specified.
+model. Alternatively, a movement direction map can be used with the
+<b>indir</b> option and the <b>-d</b> flag to trace a flow path following
+the given directions. Such a movement direction map can be generated with
+<em><a href="r.walk.html">r.walk</a></em>,
+<em><a href="r.cost.html">r.cost</a></em>,
+<em><a href="r.slope.aspect.html">r.slope.aspect</a></em> or
+<em><a href="r.watershed.html">r.watershed</a></em>.
The <b>output</b> result (also a raster map layer) will show one or more
least-cost paths between each user-provided location(s) and the minima
@@ -27,7 +30,10 @@
"slope" between adjacent cells. The slope calculation accurately acounts
for the variable scale in lat-lon projections. For a cost surface, the path
is calculated by following the movement direction surface back to the start
-point given in <em>r.walk</em> or <em>r.cost</em>.
+point given in <em>r.walk</em> or <em>r.cost</em>. The path search stops
+as soon as a region border or a neighboring NULL cell is encountered,
+because in these cases the direction can not be determined (the path
+could continue outside the current region).
<p>The <b>coordinate</b> parameter consists of map E and N grid coordinates of
a starting point. Each x,y pair is the easting and northing (respectively) of
@@ -39,9 +45,9 @@
<h2>NOTES</h2>
-<em>r.drain</em> currently finds only the lowest point
-(the cell having the smallest category value) in the
-input file that can be reached through directly adjacent cells
+If no direction input map is given, <em>r.drain</em> currently finds
+only the lowest point (the cell having the smallest category value) in
+the input file that can be reached through directly adjacent cells
that are less than or equal in value to the cell reached immediately
prior to it; therefore, it will not necessarily reach the lowest point
in the input file. It currently finds <em>pits</em> in the data, rather
@@ -62,18 +68,20 @@
<div class="code"><pre>
Input: Output:
ELEVATION SURFACE LEAST COST PATH
-. . ----- . . . . . . . . . . . . . . . . . . . . . . . . .
+. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+. 19. 20. 18. 19. 16. 15. 15. . . . . . . . .
+. . --- . . . . . . . . . . . . . . . . . . . . . . . . .
. 20| 19| 17. 16. 17. 16. 16. . . 1 . 1 . 1 . . . .
-. . |___| . . . . . . . . . . . . . . . . . . . . . . . . .
+. . --- . . . . . . . . . . . . . . . . . . . . . . . . .
. 18. 18. 24. 18. 15. 12. 11. . . . . . 1 . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. 22. 16. 16. 18. 10. 10. 10. . . . . . 1 . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. 17. 15. 15. 15. 10. 8 . 8 . . . . . . . 1 . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
-. 24. 16. 8 . 7 . 8 . 0 .12 . . . . . . . 1 . .
+. 24. 16. 8 . 7 . 8 . 0 . 12. . . . . . . 1 . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
-. 17. 9 . 8 . 7 . 8 . 6 .12 . . . . . . . . .
+. 17. 9 . 8 . 7 . 8 . 6 . 12. . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
</pre></div>
@@ -89,9 +97,11 @@
<div class="code"><pre>
Input: Output:
ELEVATION SURFACE LEAST COST PATH
-. . ----- . . . . . . . . . . . . . . . . . . . . . . . . .
+. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+. 19. 20. 18. 19. 16. 15. 15. . . . . . . . .
+. . --- . . . . . . . . . . . . . . . . . . . . . . . . .
. 20| 19| 17. 16. 17. 16. 16. . . 19. 17. 16. . . .
-. . |___| . . . . . . . . . . . . . . . . . . . . . . . . .
+. . --- . . . . . . . . . . . . . . . . . . . . . . . . .
. 18. 18. 24. 18. 15. 12. 11. . . . . . 15. . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. 22. 16. 16. 18. 10. 10. 10. . . . . . 10. . .
@@ -112,9 +122,11 @@
<div class="code"><pre>
Input: Output:
ELEVATION SURFACE LEAST COST PATH
-. . ----- . . . . . . . . . . . . . . . . . . . . . . . . .
+. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+. 19. 20. 18. 19. 16. 15. 15. . . . . . . . .
+. . --- . . . . . . . . . . . . . . . . . . . . . . . . .
. 20| 19| 17. 16. 17. 16. 16. . . 19. 36. 52. . . .
-. . |___| . . . . . . . . . . . . . . . . . . . . . . . . .
+. . --- . . . . . . . . . . . . . . . . . . . . . . . . .
. 18. 18. 24. 18. 15. 12. 11. . . . . . 67. . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. 22. 16. 16. 18. 10. 10. 10. . . . . . 77. . .
@@ -133,9 +145,11 @@
<div class="code"><pre>
Input: Output:
ELEVATION SURFACE LEAST COST PATH
-. . ----- . . . . . . . . . . . . . . . . . . . . . . . . .
+. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+. 19. 20. 18. 19. 16. 15. 15. . . . . . . . .
+. . --- . . . . . . . . . . . . . . . . . . . . . . . . .
. 20| 19| 17. 16. 17. 16. 16. . . 1 . 2 . 3 . . . .
-. . |___| . . . . . . . . . . . . . . . . . . . . . . . . .
+. . --- . . . . . . . . . . . . . . . . . . . . . . . . .
. 18. 18. 24. 18. 15. 12. 11. . . . . . 4 . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. 22. 16. 16. 18. 10. 10. 10. . . . . . 5 . . .
@@ -152,10 +166,10 @@
for the input, rather than the elevation surface. The output is then created
according to one of the <b>-can</b> flags.
<div class="code"><pre>
-The directions are recorded as GRASS standard directions:
+The directions are recorded as degrees CCW from East:
112.5 67.5 i.e. a cell with the value 135
-157.5 135 90 45 22.5 means the cell <b>before</b> it is
- 180 x 0 to the south-east.
+157.5 135 90 45 22.5 means the next cell is to the North-West
+ 180 x 0
202.5 225 270 315 337.5
247.5 292.5
</pre></div>
@@ -166,7 +180,7 @@
<p>Sometimes, when the differences among integer cell category values in the
<em><a href="r.cost.html">r.cost</a></em> cumulative cost surface output are
small, this cumulative cost output cannot accurately be used as input to
-<em>r.drain</em> (<em>t.drain</em> will output bad results).
+<em>r.drain</em> (<em>r.drain</em> will output bad results).
This problem can be circumvented by making the differences
between cell category values in the cumulative cost output bigger. It
is recommended that if the output from <em>r.cost</em> is to be used
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