Cost surfaces - Revision history

Neteler at 10:01, 4 December 2018

2018-12-04T10:01:13Z

← Older revision		Revision as of 10:01, 4 December 2018
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	'''''Q:''' I have a friction map, a start polygon and an end polygon and would like to find the '''least cost path''', meaning not a corridor but a '''thin line'''. The {{cmd\|r.drain~~\|version=70~~}} manual says: "If the input surface (a raster map layer) is a cumulative cost map generated by the {{cmd\|r.walk}} or {{cmd\|r.cost}} modules, the -d flag and a movement direction surface "indir" must be specified." I assume it's a kind of flow direction or aspect, but what is the physical meaning, and how can I calculate it?''		'''''Q:''' I have a friction map, a start polygon and an end polygon and would like to find the '''least cost path''', meaning not a corridor but a '''thin line'''. The {{cmd\|r.drain}} manual says: "If the input surface (a raster map layer) is a cumulative cost map generated by the {{cmd\|r.walk}} or {{cmd\|r.cost}} modules, the -d flag and a movement direction surface "indir" must be specified." I assume it's a kind of flow direction or aspect, but what is the physical meaning, and how can I calculate it?''

	'''A:''' The physical meaning is movement direction in degrees CCW from East, similar to e.g. flow direction output of {{cmd\|r.watershed}}. The direction map is an optional output of {{cmd\|r.cost}} and {{cmd\|r.walk}}, and should be used with the indir option for {{cmd\|r.drain}}.		'''A:''' The physical meaning is movement direction in degrees CCW from East, similar to e.g. flow direction output of {{cmd\|r.watershed}}. The direction map is an optional output of {{cmd\|r.cost}} and {{cmd\|r.walk}}, and should be used with the indir option for {{cmd\|r.drain}}.

Neteler: ref added

2016-10-25T13:03:59Z

ref added

← Older revision		Revision as of 13:03, 25 October 2016
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	r.drain -d input=dare_cost indir=dare_dir output=macon2dare vector_output=macon2dare start_coordinates=234250,147750		r.drain -d input=dare_cost indir=dare_dir output=macon2dare vector_output=macon2dare start_coordinates=234250,147750

			=== See also ===

			Application of r.walk:
			* Yang, M., van Coillie, F., Liu, M., De Wulf, R., Hens, L., & Ou, X. (2014). A GIS Approach to Estimating Tourists' Off-road Use in a Mountainous Protected Area of Northwest Yunnan, China. Mountain Research and Development, 34(2), 107-117. http://www.bioone.org/doi/full/10.1659/MRD-JOURNAL-D-13-00041.1


	[[Category: FAQ]]		[[Category: FAQ]]

⚠️Madi at 17:24, 8 January 2013

2013-01-08T17:24:31Z

@@ Line 10: / Line 10: @@
 # use the second polygon as a MASK and get the coordinates of the cell with the lowest cost
 # use these coordinates as start coordinates for r.drain, together with the movement direction map and the cumulative cost map produced by r.drain
 [[Category: FAQ]]

Neteler: new

2012-12-28T16:13:13Z

new

New page

'''''Q:''' I have a friction map, a start polygon and an end polygon and would like to find the '''least cost path''', meaning not a corridor but a '''thin line'''. The {{cmd|r.drain|version=70}} manual says: "If the input surface (a raster map layer) is a cumulative cost map generated by the {{cmd|r.walk}} or {{cmd|r.cost}} modules, the -d flag and a movement direction surface "indir" must be specified." I assume it's a kind of flow direction or aspect, but what is the physical meaning, and how can I calculate it?''

'''A:''' The physical meaning is movement direction in degrees CCW from East, similar to e.g. flow direction output of {{cmd|r.watershed}}. The direction map is an optional output of {{cmd|r.cost}} and {{cmd|r.walk}}, and should be used with the indir option for {{cmd|r.drain}}.

The workflow would thus be:

# convert the first polygon to a raster map
# use all cells of the first polygon as start points for r.walk, include the friction map
# convert the second polygon to a raster map
# use the second polygon as a MASK and get the coordinates of the cell with the lowest cost
# use these coordinates as start coordinates for r.drain, together with the movement direction map and the cumulative cost map produced by r.drain

[[Category: FAQ]]