## NAME

t.rast.what - Sample a space time raster dataset at specific vector point coordinates and write the output to stdout using different layouts

## KEYWORDS

temporal, sampling, raster, time

## SYNOPSIS

t.rast.what
t.rast.what --help
t.rast.what [-niv] [points=name] [coordinates=east,north] strds=name [output=name] [where=sql_query] [null_value=string] [separator=character] [order=string[,string,...]] [layout=string] [nprocs=integer] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

### Flags:

-n
  Output header row
-i
  Use stdin as input and ignore coordinates and point option
-v
  Show the category for vector points map
--overwrite
  Allow output files to overwrite existing files
--help
  Print usage summary
--verbose
  Verbose module output
--quiet
  Quiet module output
--ui
  Force launching GUI dialog

### Parameters:

points=name
  Name of input vector map
  Or data source for direct OGR access
coordinates=east,north
  Comma separated list of coordinates
strds=name [required]
  Name of the input space time raster dataset
output=name
  Name for the output file or "-" in case stdout should be used
  Default: -
where=sql_query
  WHERE conditions of SQL statement without 'where' keyword used in the temporal GIS framework
  Example: start_time > '2001-01-01 12:30:00'
null_value=string
  String representing NULL value
separator=character
  Field separator
  Special characters: pipe, comma, space, tab, newline
  Default: pipe
order=string[,string,...]
  Sort the maps by category
  Options: id, name, creator, mapset, creation_time, modification_time, start_time, end_time, north, south, west, east, min, max
  Default: start_time
layout=string
  The layout of the output. One point per row (row), one point per column (col), all timsteps in one row (timerow)
  Options: row, col, timerow
  Default: row
nprocs=integer
  Number of r.what processes to run in parallel
  Default: 1

## DESCRIPTION

t.rast.what is designed to sample space time raster datasets at specific point coordinates using r.what internally. The output of r.what is transformed to different output layouts. The output layouts can be specified using the layout option.

Three layouts can be specified:

- row - Row order, one vector sample point value per row
- col - Column order, create a column for each vector sample point of a single time step/raster layer
- timerow - Time order, create a column for each time step, this order is the original r.what output, except that the column names are the timestamps

Please have a look at the example to see the supported layouts.

This module is designed to run several instances of r.what to sample subsets of a space time raster dataset in parallel. Several intermediate text files will be created that are merged into a single file at the end of the processing.

Coordinates can be provided as vector map using the points option or as comma separated coordinate list with the coordinates option.

An output file can be specified using the output option. Stdout will be used if no output is specified or if the output option is set to "-".

## EXAMPLES

### Data preparation

In the following examples we sample a space time raster dataset that contains 4 raster map layers. First we create the STRDS that will be sampled with t.rast.what.

    g.region s=0 n=80 w=0 e=120 b=0 t=50 res=10

    # Generate data
    r.mapcalc expression="a_1 = 1" -s
    r.mapcalc expression="a_2 = 2" -s
    r.mapcalc expression="a_3 = 3" -s
    r.mapcalc expression="a_4 = 4" -s

    t.create type=strds output=A title="A test" descr="A test"

    t.register -i type=raster input=A maps=a_1,a_2,a_3,a_4 \
        start='1990-01-01' increment="1 month"

### Example 1

The first approach uses text coordinates as input and stdout as output, the layout is one coordinate(point per column:

    t.rast.what strds=A coordinates="115,36,79,45" layout=col -n

    start|end|115.0000000000;36.0000000000|79.0000000000;45.0000000000
    1990-01-01 00:00:00|1990-02-01 00:00:00|1|1
    1990-02-01 00:00:00|1990-03-01 00:00:00|2|2
    1990-03-01 00:00:00|1990-04-01 00:00:00|3|3
    1990-04-01 00:00:00|1990-05-01 00:00:00|4|4

### Example 2

A vector map layer can be used as input to sample the STRDS. All three available layouts are demonstrated using the vector map for sampling.

    # First create the vector map layer based on random points
    v.random output=points n=3 seed=1

    # Row layout using a text file as output
    t.rast.what strds=A points=points output=result.txt layout=row -n

    cat result.txt

    115.0043586274|36.3593955783|1990-01-01 00:00:00|1990-02-01 00:00:00|1
    115.0043586274|36.3593955783|1990-02-01 00:00:00|1990-03-01 00:00:00|2
    115.0043586274|36.3593955783|1990-03-01 00:00:00|1990-04-01 00:00:00|3
    115.0043586274|36.3593955783|1990-04-01 00:00:00|1990-05-01 00:00:00|4
    79.6816763826|45.2391522853|1990-01-01 00:00:00|1990-02-01 00:00:00|1
    79.6816763826|45.2391522853|1990-02-01 00:00:00|1990-03-01 00:00:00|2
    79.6816763826|45.2391522853|1990-03-01 00:00:00|1990-04-01 00:00:00|3
    79.6816763826|45.2391522853|1990-04-01 00:00:00|1990-05-01 00:00:00|4
    97.4892579600|79.2347263950|1990-01-01 00:00:00|1990-02-01 00:00:00|1
    97.4892579600|79.2347263950|1990-02-01 00:00:00|1990-03-01 00:00:00|2
    97.4892579600|79.2347263950|1990-03-01 00:00:00|1990-04-01 00:00:00|3
    97.4892579600|79.2347263950|1990-04-01 00:00:00|1990-05-01 00:00:00|4

    # Column layout order using stdout as output
    t.rast.what strds=A points=points layout=col -n

    start|end|115.0043586274;36.3593955783|79.6816763826;45.2391522853|97.4892579600;79.2347263950
    1990-01-01 00:00:00|1990-02-01 00:00:00|1|1|1
    1990-02-01 00:00:00|1990-03-01 00:00:00|2|2|2
    1990-03-01 00:00:00|1990-04-01 00:00:00|3|3|3
    1990-04-01 00:00:00|1990-05-01 00:00:00|4|4|4

    # Timerow layout, one time series per row
    # using the where statement to select a subset of the STRDS
    # and stdout as output
    t.rast.what strds=A points=points \
        where="start_time >= '1990-03-01'" layout=timerow -n

    x|y|1990-03-01 00:00:00;1990-04-01 00:00:00|1990-04-01 00:00:00;1990-05-01 00:00:00
    115.004358627375|36.3593955782903|3|4
    79.681676382576|45.2391522852909|3|4
    97.4892579600048|79.2347263950131|3|4

## SEE ALSO

g.region, r.mask r.neighbors, r.what, t.info, t.rast.aggregate.ds, t.rast.extract, v.what.strds

## AUTHOR

Sören Gebbert, Thünen Institute of Climate-Smart Agriculture

## SOURCE CODE

Available at: t.rast.what source code (history)

Latest change: Mon Nov 18 20:15:32 2019 in commit: 1a1d107e4f6e1b846f9841c2c6fabf015c5f720d

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