Pktools - Open Source Geospatial Tools: Applications in Earth Observation - page 176

-geo|--geo
Use geo coordinates (set to 0 to use image coordinates) (default: 1).
-down|--down
Down sampling factor (for raster sample datasets only). Can be used to create
grid points (default: 1).
-buf|--buffer
Buffer for calculating statistics for point features.
-circ|--circular
Use a circular disc kernel buffer (for vector point sample datasets only, use in
combination with buffer option) (default: false).

An overview of the possible extraction rules is given in Table 12.1 . For point
features, some exraction rules require a buffer, which size is set via option -buf (e.g.
mean).
The first example prepares a training set for the classifiers implemented in pktools.
In this example, the training is based on a sample of points, written in a Spatialite file. 4
The raster from which to extract the points is a multiband dataset that is composed
of 145 bands. The first band contains a digital surface model derived from LiDAR.
The remaining bands correspond to a hyperspectral image with 144 spectral bands
obtained from the compact airborne spectrographic imager (CASI). The resulting
vector file will thus contain a copy of all attributes from the sample vector file as well
as an attribute for each of the 145 bands. A subset of the training data for different
classes of grass is shown in Fig. 12.2 a. The mean and standard deviation of the

Table 12.1 Rules for extracting raster pixel values with pkextract based on a vector sample
Extraction rule Result

Extract all pixel values covered by the polygon (option -polygon not set)
or extract a pixel on the surface option ( -polygon is set)

point

centroid Extract pixel value at the centroid of the polygon

Extract average of all pixel values within the polygon

mean

Extract standard deviation of all pixel values within the polygon

stdev

median Extract median of all pixel values within the polygon

Extract minimum value of all pixels within the polygon

minimum

Extract maximum value of all pixels within the polygon

maximum

sum Extract sum of the values of all pixels within the polygon

Extract the mode of classes within the polygon (classes must be set with
the option -c|-class )

mode

proportion Extract proportion of class(es) within the polygon (classes must be set with

the option -c|-class )

4 2013_IEEE_GRSS_DF_Contest_Samples_TR_26915.sqlite