Hi,
I need to add some attributes from a soil polygon layer to a catchment
polygon layer using area weighting. In other words, the contribution
of the soil layer needs to be weighted by the amount with which its
polygons overlap the catchment polygons.
For example, suppose I want to weight soil infiltration rates. 30% of
a catchment polygon overlaps with soil type 1 and 70% overlaps with
soil type 2. Now I want a new attribute in the catchment polygon that
takes 30% of the infiltration rate of soil type 1 and adds it to 70%
of the infiltration rate of soil type 2.
How can I do this in GRASS?
Thanks
Hanlie
On 11/03/2010 04:55 PM, Hanlie Pretorius wrote:
Hi,
I need to add some attributes from a soil polygon layer to a catchment
polygon layer using area weighting. In other words, the contribution
of the soil layer needs to be weighted by the amount with which its
polygons overlap the catchment polygons.
For example, suppose I want to weight soil infiltration rates. 30% of
a catchment polygon overlaps with soil type 1 and 70% overlaps with
soil type 2. Now I want a new attribute in the catchment polygon that
takes 30% of the infiltration rate of soil type 1 and adds it to 70%
of the infiltration rate of soil type 2.
How can I do this in GRASS?
The most straight forward way is using v.rast.stats. This module adds to a vector attribute table the univariate statistics from a raster. So you'll first convert the soil map to raster, then run v.rast.stats using the catchment polygons as the vector and the soil infiltration as the raster.
Thanks
Hanlie
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Micha Silver
Arava Development Co. +972-52-3665918
http://surfaces.co.il
2010/11/3, Micha Silver <micha@arava.co.il>:
On 11/03/2010 04:55 PM, Hanlie Pretorius wrote:
Hi,
I need to add some attributes from a soil polygon layer to a catchment
polygon layer using area weighting. In other words, the contribution
of the soil layer needs to be weighted by the amount with which its
polygons overlap the catchment polygons.
For example, suppose I want to weight soil infiltration rates. 30% of
a catchment polygon overlaps with soil type 1 and 70% overlaps with
soil type 2. Now I want a new attribute in the catchment polygon that
takes 30% of the infiltration rate of soil type 1 and adds it to 70%
of the infiltration rate of soil type 2.
How can I do this in GRASS?
The most straight forward way is using v.rast.stats. This module adds to
a vector attribute table the univariate statistics from a raster. So
you'll first convert the soil map to raster, then run v.rast.stats using
the catchment polygons as the vector and the soil infiltration as the
raster.
Thanks, this worked.
Is there a reason (other than no one has had time to do it) that a
similar function doesn't exist for two vector layers?
On 04/11/2010 10:56, Hanlie Pretorius wrote:
2010/11/3, Micha Silver<micha@arava.co.il>:
On 11/03/2010 04:55 PM, Hanlie Pretorius wrote:
Hi,
I need to add some attributes from a soil polygon layer to a catchment
polygon layer using area weighting. In other words, the contribution
of the soil layer needs to be weighted by the amount with which its
polygons overlap the catchment polygons.
For example, suppose I want to weight soil infiltration rates. 30% of
a catchment polygon overlaps with soil type 1 and 70% overlaps with
soil type 2. Now I want a new attribute in the catchment polygon that
takes 30% of the infiltration rate of soil type 1 and adds it to 70%
of the infiltration rate of soil type 2.
How can I do this in GRASS?
The most straight forward way is using v.rast.stats. This module adds to
a vector attribute table the univariate statistics from a raster. So
you'll first convert the soil map to raster, then run v.rast.stats using
the catchment polygons as the vector and the soil infiltration as the
raster.
Thanks, this worked.
Is there a reason (other than no one has had time to do it) that a
similar function doesn't exist for two vector layers?
The general case is that some value varies continuously over a region - suppose, for example, that your soil infiltration was some continuously changing value and not discrete polygons. Averaging (or other stats) over the raster cell values is the way to get statistics from one spatial phenomenon into another.
This mail was received via Mail-SeCure System.
--
Micha Silver
http://www.surfaces.co.il/
Arava Development Co. +972-52-3665918