DESCRIPTION
Determine the functional nearest-neighbor distance analysis.
r.pi.fnn is a patch based ecological/functional nearest
neighbour analysis module. It computes distance based on a friction
map. This module is related to r.pi.enn but more adequate if
the ecological connectivity should be analysed.
NOTES
The calculation of the ecolgogical nearest neighbour is based on a raster
with start patches. The actual map can be categorical or continuous but
the value defined in keyval will be the basis for the patches
to calculate the methods defined below. These patches will also be in
the output map.
The calculation of the ecolgogical nearest neighbour is based on a costmap
(* and 1-infinite) - this map can be binary or continous - high values
are considered to have high cost issues and the shortest path is the
one with the lowest amount of costs. "null" values can not be traversed,
hence these values have to be bypassed. "0" values are not accepted and
will result in "0" distance.
e.g. if a binary map(1 and 2) is used, the the path with the
lowest amount of "1" is chosen
The number is the amount of nearest neighbours to be taken and
the calculated distances are processed as assigned in statmethod
Operations which r.pi.fnn can perform are:
- Distance
- The Distance to Nearest computes the nearest edge-to-edge
distance between patches. Counting from the focus patch.
- path Distance
- The Distance to Nearest computes the nearest edge-to-edge
distance between patches. Unlike Distance the distance is
computed based on subsequent NN not from the focus patch onwards. The
1th NN is the first patch with the minimal edge-to-edge distance from
the focus patch, while 2th NN is the patch with the minimal edge-to-edge
distance from the 1th NN patch and so on.
- Area
- The Area computes the size of the nearest edge-to-edge
distance patch. It is based on Distance not on path Distance.
- Perimeter
- The Perimeter computes the Perimeter of the nearest
edge-to-edge distance patch. It is based on Distance not on
path Distance.
- SHAPE
- The SHAPE computes the SHAPE Index of the nearest edge-to-edge
distance patch. It is based on Distance not on path Distance.
The statsmethod operators determine calculation is done on the
distance. Average, Variance,Stddev and
value can be used.
- Average
- The Average computes the average value defined in
Operations to perform .
- Variance
- The Variance computes the variance defined in
Operations to perform .
- Stand. Dev.
- The Stand. Dev. computes the stddev value defined in
Operations to perform .
- Value
- The patch Distance computes the nearest edge-to-edge distance
between two patches. The output of value is the actual value.
E.g. NN==5 of area gives the size of the 5th NN while
Average gives the average of the area of 1-5th NN.
The input options are either one NN: 1 or several NN separated
by ,: 1,2,5,8 or a range of NN: 1-6.
Merging these options is possible as well: 1-5,8,9,13,15-19,22 etc.
EXAMPLE
An example for the North Carolina sample dataset:
Computing the functional or ecological distance to the first to nth
nearest neighrbours using a cost matrix:
r.mapcalc "cost_raster = if(landclass96==5,1,if(landclass96 == 1, 10, if (landclass96==3,2, if(landclass96==4,1,if(landclass96==6,100)))))"
r.pi.fnn input=landclass96 keyval=5 costmap=cost_raster output=fnn1 method=distance number=10 statmethod=average
SEE ALSO
r.pi.enn,
r.pi.index,
r.pi
AUTHORS
Programming: Elshad Shirinov
Scientific concept: Dr. Martin Wegmann
Department of Remote Sensing
Remote Sensing and Biodiversity Unit
University of Wuerzburg, Germany
Port to GRASS GIS 7: Markus Metz
Last changed: $Date$