Creating Patch Maps - Revision history

Dgroulx at 21:37, 4 January 2010

2010-01-04T21:37:55Z

Dgroulx: /* DEM Pixels */

2009-12-02T13:10:50Z

DEM Pixels

Dgroulx: /* Altitude/Basin Cuts */

2009-11-29T20:53:40Z

Altitude/Basin Cuts

Dgroulx: /* Altitude/Basin Cuts */

2009-11-29T20:53:23Z

Altitude/Basin Cuts

Dgroulx at 18:54, 29 November 2009

2009-11-29T18:54:16Z

Dgroulx at 18:54, 29 November 2009

2009-11-29T18:54:01Z

Dgroulx: /* Clumps */

2009-11-29T18:53:51Z

Clumps

Dgroulx at 18:53, 29 November 2009

2009-11-29T18:53:26Z

Dgroulx at 04:09, 29 November 2009

2009-11-29T04:09:19Z

Dgroulx: /* DEM Pixels */

2009-11-29T04:09:07Z

DEM Pixels

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-A patch is the smallest spacial level in RHESSys.  This is where the majority of computation happens.  Creating a good patch map is a balance between using enough patches to capture the behavior of your watershed, but using few enough to keep computation times reasonable.  There is no single best way to create patch maps, as the ideal patch map will change depending on both your actual watershed, and the questions are you are asking.  The following are a few methods that RHESSys users have had success with.
+A patch is the smallest spacial level in RHESSys.  This is where the majority of computation happens.  Creating a good patch map is a balance between using enough patches to capture the behavior of your watershed, but using few enough to keep computation times reasonable.  There is no single best way to create patch maps, as the ideal patch map will change depending on both your actual watershed, and the questions you are asking.  The following are a few methods that RHESSys users have had success with.  Users should feel free to append any methods that they like and the problem they were examining to this page.
 A general rule for thinking about your patches, you want them to be homogenius with respect to the property you are interested in, and heterogenius
-with respect to most other inputs.  For example if you are curious about effects of vegetation, it may
+with respect to most other inputs.  For example if you are curious about effects of vegetation, it may be useful to incorporate your vegetation map
 ====DEM Pixels====
-The most straightforward way is to use each DEM pixel as a patch.  This method is nice as it will capture all possible variation within your watershed.  However it is also the most computationally expensive, and will only work for very small watersheds.
+The most straightforward way is to use each DEM pixel as a patch.  This method is nice as it will capture all possible topographic variation within your watershed.  However it is also the most computationally expensive, and will only work for very small watersheds.
 To create this map, you need to convert the DEM to a map of unique integers.  This can be done based on the row and column index of the DEM cell.

@@ Line 10: / Line 10: @@
 First you need to find out how many columns are in your DEM.
-Use the command <code>G> r.info <DEM name></code> to find the number of columns.  Once you know that, yo
+Use the command <code>G> r.info <DEM name></code> to find the number of columns.  Once you know that, you run
 <code>G> r.mapcalc 'patch_map = row()*<number of columns> + col()'</code>

← Older revision		Revision as of 20:53, 29 November 2009
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	alt_bands will be broken up into 30 bands. In order to break these bands up by hillslopes, you will add the two maps together. The catch is to multiply the hillslope map by a large enough number so that each hillslope/alt_band combination is a unique number. Chose a power of ten greater than the number of altitude bands, in this case, 100. Then compute the final patch map as		alt_bands will be broken up into 30 bands. In order to break these bands up by hillslopes, you will add the two maps together. The catch is to multiply the hillslope map by a large enough number so that each hillslope/alt_band combination is a unique number. Chose a power of ten greater than the number of altitude bands, in this case, 100. Then compute the final patch map as

−	<code>G> r.mapcalc '~~patches~~ = hillslope * 100 + alt_bands'</code>	+	<code>G> r.mapcalc 'patch_map = hillslope * 100 + alt_bands'</code>

← Older revision		Revision as of 20:53, 29 November 2009
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	====Altitude/Basin Cuts====		====Altitude/Basin Cuts====
−	This method will allow you to create far fewer patches than DEM pixels or the clumping methods, while still preserving the hydrological soundness of your patches. The idea is to break up the watershed into altitude bands, then intersect these bands with the hillslope map. You can use the	+	This method will allow you to create far fewer patches than DEM pixels or the clumping methods, while still preserving the hydrological soundness of your patches. The idea is to break up the watershed into altitude bands, then intersect these bands with the hillslope map. You can use the hillslope map that
		+	you generated for the hillslope level in your worldfile template using r.watershed, or you can create a higher resolution hillslope.
		+
		+	First, cut the DEM into bands by altitude. For example, if your DEM spans 3000m,
		+
		+	<code>G> r.mapcalc 'alt_bands = int(DEM / 100)'</code>
		+
		+	alt_bands will be broken up into 30 bands. In order to break these bands up by hillslopes, you will add the two maps together. The catch is to multiply the hillslope map by a large enough number so that each hillslope/alt_band combination is a unique number. Chose a power of ten greater than the number of altitude bands, in this case, 100. Then compute the final patch map as
		+
		+	<code>G> r.mapcalc 'patches = hillslope * 100 + alt_bands'</code>

@@ Line 3: / Line 3: @@
 A general rule for thinking about your patches, you want them to be homogenius with respect to the property you are interested in, and heterogenius
 with respect to most other inputs.  For example if you are curious about effects of vegetation, it may
 ====DEM Pixels====
@@ Line 14: / Line 13: @@
 <code>G> r.mapcalc 'patch_map = row()*<number of columns> + col()'</code>
 ====Clumps====
@@ Line 20: / Line 18: @@
 <code>G> r.clump input=<DEM name> output=<patchmap name></code>
 ====Altitude/Basin Cuts====
 This method will allow you to create far fewer patches than DEM pixels or the clumping methods, while still preserving the hydrological soundness of your patches.  The idea is to break up the watershed into altitude bands, then intersect these bands with the hillslope map. You can use the

← Older revision		Revision as of 04:09, 29 November 2009
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−	===DEM Pixels===	+	====DEM Pixels====
−

	===Clumps===		===Clumps===