pkextractogr

extract pixel values from raster image using a vector dataset sample

SYNOPSIS

Usage: pkextractogr -i input [-s sample | -rand number | -grid size] -o output

Options: [-ln layer]* [-c class]* [-t threshold]* [-f format] [-ft fieldType] [-b band]* [-r rule]*

Advanced options: [-sband band -eband band]* [-bndnodata band -srcnodata value]* [-tp threshold] [-buf value [-circ]]

Description

The utility 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:

pkextractogr_rules

extraction rule	output features
point	extract a single pixel within the polygon or on each point feature
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)

Options

• use either -short or --long options (both --long=value and --long value are supported)
• short option -h shows basic options only, long option --help shows all options

  short	long	type	default	description
  i	input	std::string		Raster input dataset containing band information
  s	sample	std::string		OGR vector dataset with features to be extracted from input data. Output will contain features with input band information included
  ln	ln	std::string		Layer name(s) in sample (leave empty to select all)
  rand	random	unsigned int		Create simple random sample of points. Provide number of points to generate
  grid	grid	double		Create systematic grid of points. Provide cell grid size (in projected units, e.g,. m)
  o	output	std::string		Output sample dataset
  c	class	int		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	float	100	Probability threshold for selecting samples (randomly). Provide probability in percentage (>0) or absolute (<0). Use a single threshold per vector sample layer
  perc	perc	double	95	Percentile value used for rule percentile
  f	f	std::string	SQLite	Output sample dataset format
  ft	ftype	std::string	Real	Field type (only Real or Integer)
  b	band	int		Band index(es) to extract (0 based). Leave empty to use all bands
  sband	startband	unsigned short		Start band sequence number
  eband	endband	unsigned short		End band sequence number
  r	rule	std::string	centroid	Rule how to report image information per feature (only for vector sample). point (single point or at centroid if polygon), allpoints (within polygon), centroid, mean, stdev, median, proportion, count, min, max, mode, sum, percentile.
  bndnodata	bndnodata	int	0	Band(s) in input image to check if pixel is valid (used for srcnodata)
  srcnodata	srcnodata	double		Invalid value(s) for input image
  tp	thresholdPolygon	float		(absolute) threshold for selecting samples in each polygon
  buf	buffer	short	0	Buffer for calculating statistics for point features (in number of pixels)
  circ	circular	bool	false	Use a circular disc kernel buffer (for vector point sample datasets only, use in combination with buffer option)

  Usage: pkextractogr -i input [-s sample | -rand number | -grid size] -o output -r rule

Examples

Some examples how to use pkextractogr can be found here