pkextractogr - extract pixel values from raster image from a
(vector or raster) sample
pkextractogr
-i input [-s sample | -rand number |
-grid size] -o output [options]
pkextractogr extracts pixel values from an input raster
dataset, based on the locations you provide via a sample file.
Alternatively, a random sample or systematic grid of points can also be
extracted. The sample can be a vector file with points or polygons. In the
case of polygons, you can either extract the values for all raster pixels
that are covered by the polygons, or extract a single value for each polygon
such as the centroid, mean, median, etc. As output, a new copy of the vector
file is created with an extra attribute for the extracted pixel value. For
each raster band in the input image, a separate attribute is created. For
instance, if the raster dataset contains three bands, three attributes are
created (b0, b1 and b2).
A typical usage of pkextractogr is to prepare a training
sample for one of the classifiers implemented in pktools.
Overview of the possible extraction rules:
| Extraction rule |
Output features |
| point |
Extract all pixel values covered by the polygon (option -polygon
not set) or extract a pixel on the surface option (-polygon
set). |
| allpoints |
Extract all pixel values covered by the polygon. |
| centroid |
Extract pixel value at the centroid of the polygon. |
| mean |
Extract average of all pixel values within the polygon. |
| stdev |
Extract standard deviation of all pixel values within the polygon. |
| median |
Extract median of all pixel values within the polygon. |
| min |
Extract minimum value of all pixels within the polygon. |
| max |
Extract maximum value of all pixels within the polygon. |
| sum |
Extract sum of the values of all pixels within the polygon. |
| mode |
Extract the mode of classes within the polygon (classes must be set with
the option class). |
| proportion |
Extract proportion of class(es) within the polygon (classes must be set
with the option class). |
| count |
Extract count of class(es) within the polygon (classes must be set with
the option class). |
| percentile |
Extract percentile as defined by option perc (e.g, 95th percentile of
values covered by polygon). |
- -i filename,
--input filename
- Raster input dataset containing band information
- -s sample,
--sample sample
- OGR vector dataset with features to be extracted from input data. Output
will contain features with input band information included. Sample image
can also be GDAL raster dataset.
- -ln layer,
--ln layer
- Layer name(s) in sample (leave empty to select all)
- -rand number,
--random number
- Create simple random sample of points. Provide number of points to
generate
- -grid size,
--grid size
- Create systematic grid of points. Provide cell grid size (in projected
units, e.g,. m)
- -o filename,
--output filename
- Output sample dataset Output sample dataset
- -c class,
--class class
- Class(es) to extract from input sample image. Leave empty to extract all
valid data pixels from sample dataset. Make sure to set classes if rule is
set to mode, proportion or count.
- -t threshold,
--threshold threshold
- Probability threshold for selecting samples (randomly). Provide
probability in percentage (>0) or absolute (<0). Use a single
threshold per vector sample layer. If using raster land cover maps as a
sample dataset, you can provide a threshold value for each class (e.g.
-t 80 -t 60). Use value 100 to select all
pixels for selected class(es)
- -perc
percentile, --perc percentile
- Percentile value used for rule percentile
- -f format, --f
format
- Output sample dataset format
- -ft fieldType,
--ftype fieldType
- Field type (only Real or Integer)
- -lt labelType,
--ltype labelType
- Label type: In16 or String
- -b band, --band
band
- Band index(es) to extract. Leave empty to use all bands
- -sband band,
--startband band
- Start band sequence number
- -eband band,
--endband band
- End band sequence number
- -r rule, --rule
rule
- Rule how to report image information per feature (only for vector sample).
point (value at each point or at centroid if polygon), centroid, mean,
stdev, median, proportion, count, min, max, mode, sum, percentile.
- -bndnodata
band, --bndnodata band
- Band(s) in input image to check if pixel is valid (used for
srcnodata)
- -srcnodata
value, --srcnodata value
- Invalid value(s) for input image
- -tp threshold,
--thresholdPolygon threshold
- (absolute) threshold for selecting samples in each polygon
- -buf value,
--buffer value
- 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)
- -v level,
--verbose level
- Verbose mode if > 0