r.accumulate: Update the manual (#165)

* r.accumulate: Update the manual

* Wrap long lines in <pre>

* Use an existing variable instead of calling get()

grass7/raster/r.accumulate/calculate_lfp.c

@@ -210,7 +210,7 @@ static int trace_up(struct cell_map *dir_buf, struct raster_map *accum_buf,
                 if (up_acc < cur_acc) {
                     up_accum[nup].row = row + i;
                     up_accum[nup].col = col + j;
-                    up_accum[nup++].accum = get(accum_buf, row + i, col + j);
+                    up_accum[nup++].accum = up_acc;
                 }
             }
         }

grass7/raster/r.accumulate/r.accumulate.html

@@ -135,7 +135,8 @@ <h3>Stream network delineation</h3>
 r.accumulate direction=drain_directions threshold=50000 stream=streams_new_only
 
 # use r.stream.extract, elevation, and flow_accum_new to delineate stream networks
-r.stream.extract elevation=elevation accumulation=flow_accum threshold=50000 stream_vector=streams_extract direction=drain_directions_extract
+r.stream.extract elevation=elevation accumulation=flow_accum threshold=50000 stream_vector=streams_extract \
+    direction=drain_directions_extract
 </pre></div>
 
 <img src="r_accumulate_nc_stream_example.png">
@@ -186,10 +187,10 @@ <h3>Longest flow path calculation</h3>
 r.watershed elevation=elevation drainage=drain_directions -s -a
 
 # calculate longest flow paths at two outlets
-r.accumulate direction=drain_directions lfp=lfp coordinates=642455,222614,642306,222734
+r.accumulate direction=drain_directions lfp=lfp coordinates=642455,222614,642314,222734
 
 # calculate longest flow paths at two outlets and assign IDs
-r.accumulate direction=drain_directions lfp=lfp_w_id coordinates=642455,222614,642306,222734 \
+r.accumulate direction=drain_directions lfp=lfp_w_id coordinates=642455,222614,642314,222734 \
     id=1,2 id_column=lfp_id
 
 # calculate longest flow paths at all points in the outlets map
@@ -200,11 +201,13 @@ <h3>Longest flow path calculation</h3>
     id_column=lfp_id outlet_id_column=outlet_id
 
 # calculate longest flow paths at given coordinates and all points in the outlets map and assign IDs
-r.accumulate direction=drain_directions lfp=lfp_multi_w_id coordinates=642455,222614,642306,222734 outlet=outlets \
-    id=1,2 id_column=lfp_id outlet_id_column=outlet_id
+r.accumulate direction=drain_directions lfp=lfp_multi_w_id coordinates=642455,222614,642314,222734 \
+    outlet=outlets id=1,2 id_column=lfp_id outlet_id_column=outlet_id
 </pre></div>
 
-<p>Calculate the longest flow paths for sub-watersheds:
+<p><img src="r_accumulate_nc_lfp_example_multiple.png">
+
+<p>Calculate the longest flow paths for subwatersheds:
 <div class="code"><pre>
 # set computational region
 g.region raster=elevation -p
@@ -219,7 +222,7 @@ <h3>Longest flow path calculation</h3>
 r.accumulate direction=drain_directions threshold=50000 stream=streams
 
 # populate stream lengths
-v.db.addtable map=streams columns="length double"
+v.db.addtable map=streams
 v.to.db map=streams option=length columns=length
 
 # create points along the streams starting from downstream
@@ -233,10 +236,29 @@ <h3>Longest flow path calculation</h3>
 v.extract input=stream_points layer=2 cats=$cats output=stream_outlets
 
 # create the longest flow paths for all outlets
-r.accumulate direction=drain_directions lfp=lfp id_column=id outlet=stream_outlets outlet_layer=2 outlet_id_column=lcat
+r.accumulate direction=drain_directions lfp=lfp id_column=id \
+    outlet=stream_outlets outlet_layer=2 outlet_id_column=lcat
+
+# delineate subwatersheds
+i=1
+for coor in `v.report -c map=stream_outlets layer=2 option=coor | awk -F'|' '{printf "%s,%s\n", $4, $5}'`; do
+    r.water.outlet --o input=drain_directions output=tmp coordinates=$coor
+    r.mapcalc expression="subwatershed_$i=if(isnull(tmp),0,1&lt;&lt;($i-1))"
+    i=`expr $i + 1`
+done
+
+# patch subwatersheds
+subwatersheds=`g.list type=rast pattern=subwatershed_* sep=+`
+r.mapcalc express="subwatersheds=if($subwatersheds,$subwatersheds,null())"
+
+# convert subwatersheds to vector
+r.to.vect input=subwatersheds type=area output=subwatersheds
+
+# delete subwatershed rasters
+g.remove -f type=rast pattern=subwatershed*
 </pre></div>
 
-<img src="r_accumulate_nc_lfp_example_multiple.png">
+<img src="r_accumulate_nc_lfp_example_subwatersheds.png">
 
 <h2>SEE ALSO</h2>