Exercise: A spatial model of a catchment - Revision history

Wiki-Ajolma at 17:29, 28 May 2006

2006-05-28T17:29:58Z

Wiki-Ajolma at 17:25, 28 May 2006

2006-05-28T17:25:43Z

Wiki-Ajolma at 17:21, 28 May 2006

2006-05-28T17:21:37Z

Wiki-Ajolma at 17:11, 28 May 2006

2006-05-28T17:11:29Z

Wiki-Ajolma at 17:11, 28 May 2006

2006-05-28T17:11:09Z

Wiki-Ajolma at 17:10, 28 May 2006

2006-05-28T17:10:41Z

Wiki-Ajolma at 17:10, 28 May 2006

2006-05-28T17:10:10Z

New page

Note 1: this exercise is designed to be used with libral and Gtk2::Ex::Geo tools.
Note 2: the tools have to be currently the CVS versions

Required data: a land cover raster and a DEM

["http://map.hut.fi/PerlForGeoinformatics/", More information about the tools]

Steps of the exercise:

# open land cover raster

# zoom to probable catchment area (rather too large than too small!)

# clip a piece of the land cover, name it "lc" (*)

# make a 'lakes' raster by saying $lakes = $lc == 43 (or whatever the land cover code for water is) [TODO: add instructions for removing streams from the lakes raster]

# give unique id's for all lakes: $lakes->number_areas

# open a DEM raster

# clip a similar piece(***) of the dem, name it 'dem'

# compute pitless flow direction grid: say(**) $fdg = $dem->filldepressions (*4)

# fix the FDG so that each lake has one and only one outlet, say: $fdg->kill_extra_outlets($lakes)

# compute upslope area grid, say: $uag = $fdg->uag

# search for the catchment (lake) outlet cell and compute a catchment raster: $c = $fdg->catchment(<coordinates>)

# compute a streams raster from the $uag: $s = $uag > x

# remove very short streams: $s->prune($fdg, $lakes, <coordinates>, $l)

# give unique id's for each stream segment: $s->number_streams($fdg, <coordinates>);

# compute a subcatchments raster and topology information: ($sc, $topo) = $s->subcatchments($fdg, $lakes, <coordinates>)

# save the subcatchment structure as an OGR vector layer: $sc->save_catchment_structure($topo, $s, $lakes, $ogr_datasource, $layer)

footnotes:

(*) the clipped piece is automatically a plain libral raster, it may (and should) be saved by saying(**) $lc-save('lc'); later the saved raster may be opened in the usual way, but it needs to be "librated" by clipping to <self>

(**) "say", means write to the combo box, i.e. the command line interface

(***) in the clip dialog, select a raster to make a raster that is overlayable to it

(*4) this can be checked by saying: p($self,$fdg->contents), which computes the contents (number of cells having different values) and prints it

@@ Line 1: / Line 1: @@
 Note 1: this exercise is designed to be used with libral and Gtk2::Ex::Geo tools.
-Note 2: the tools have to be currently the CVS versions
+Note 2: the tools have to be currently the CVS versions.
-Required data: a land cover raster and a DEM
+Required data: a land cover raster and a DEM.
-Results: the hydrological structure (lakes, subcatchments, stream sections, and their topological structure) of a catchment as a vector layer
+Results: the hydrological structure (lakes, subcatchments, stream sections, and their topological structure) of a catchment as a vector layer.
 Students should follow the outline below and do the same procedure for a catchment of their own selection. Each step may involve explanations by the teacher.

← Older revision		Revision as of 17:21, 28 May 2006
Line 3:		Line 3:

	Required data: a land cover raster and a DEM		Required data: a land cover raster and a DEM
		+	Results: the hydrological structure (lakes, subcatchments, stream sections, and their topological structure) of a catchment as a vector layer
		+
		+	Students should follow the outline below and do the same procedure for a catchment of their own selection. Each step may involve explanations by the teacher.

	[http://map.hut.fi/PerlForGeoinformatics/ More information about the tools]		[http://map.hut.fi/PerlForGeoinformatics/ More information about the tools]

@@ Line 4: / Line 4: @@
 Required data: a land cover raster and a DEM
-[http://map.hut.fi/PerlForGeoinformatics/, More information about the tools]
+[http://map.hut.fi/PerlForGeoinformatics/ More information about the tools]
 Steps of the exercise:

@@ Line 27: / Line 27: @@
 # compute a subcatchments raster and topology information: ($sc, $topo) = $s->subcatchments($fdg, $lakes, <coordinates>)
 # save the subcatchment structure as an OGR vector layer: $sc->save_catchment_structure($topo, $s, $lakes, $ogr_datasource, $layer)
 footnotes:

@@ Line 9: / Line 9: @@
 # open land cover raster
 # zoom to probable catchment area (rather too large than too small!)
 # clip a piece of the land cover, name it "lc" (*)
 # make a 'lakes' raster by saying $lakes = $lc == 43 (or whatever the land cover code for water is) [TODO: add instructions for removing streams from the lakes raster]
 # give unique id's for all lakes: $lakes->number_areas
 # open a DEM raster
 # clip a similar piece(***) of the dem, name it 'dem'
 # compute pitless flow direction grid: say(**) $fdg = $dem->filldepressions (*4)
 # fix the FDG so that each lake has one and only one outlet, say: $fdg->kill_extra_outlets($lakes)
 # compute upslope area grid, say: $uag = $fdg->uag
 # search for the catchment (lake) outlet cell and compute a catchment raster: $c = $fdg->catchment(<coordinates>)
 # compute a streams raster from the $uag: $s = $uag > x
 # remove very short streams: $s->prune($fdg, $lakes, <coordinates>, $l)
 # give unique id's for each stream segment: $s->number_streams($fdg, <coordinates>);
 # compute a subcatchments raster and topology information: ($sc, $topo) = $s->subcatchments($fdg, $lakes, <coordinates>)
 # save the subcatchment structure as an OGR vector layer: $sc->save_catchment_structure($topo, $s, $lakes, $ogr_datasource, $layer)