## DESCRIPTION

The purpose of t.sample is to compute and to show spatio-temporal relations between space time datasets of different type. Several input space time datasets are sampled by a sample space time dataset using temporal topological relations. The types of the input space time datasets and the type of the sample space time dataset can be different.

This module is useful to analyze temporal relationships between space time datasets using temporal topology. The flag -s enables a spatio-temporal topology, so that only spatio-temporal related map layers of space time datasets are considered in the analysis.

## NOTES

The temporal relation start means that the start time of an input map layer is temporally located in an interval of a sample map layer.

The textual output at the command line shows the names of the maps, start and end time as well as the interval length in days and the temporal distance from begin in days.

The default separator is the pipe symbol.

Temporal gaps, if present, in the input and sampling space time datasets will be used in the sampling process. Gaps have no map name, instead None is printed.

## EXAMPLE

In the examples below we create a space time raster dataset A and a space time vector dataset P that have different temporal layouts and number of map layers. The space time vector dataset contains a gap, that will be used in the sampling process.

We use t.sample to inspect the topological relations between the time stamped map layers in A and P.

    # Set an appropriate region
    g.region s=0 n=80 w=0 e=120 b=0 t=50 res=10 res3=10 -p3

    # Generate the raster map layer
    r.mapcalc expression="a1 = rand(0, 550)" -s
    r.mapcalc expression="a2 = rand(0, 450)" -s
    r.mapcalc expression="a3 = rand(0, 320)" -s
    r.mapcalc expression="a4 = rand(0, 510)" -s
    r.mapcalc expression="a5 = rand(0, 300)" -s
    r.mapcalc expression="a6 = rand(0, 650)" -s

    # Generate the vector map layer
    v.random -z output=pnts1 n=20 zmin=0 zmax=100 column=height
    v.random -z output=pnts2 n=20 zmin=0 zmax=100 column=height

    n1=`g.tempfile pid=1 -d`
    n2=`g.tempfile pid=2 -d`

    cat > "${n1}" << EOF
    a1
    a2
    a3
    a4
    a5
    a6
    EOF

    cat > "${n2}" << EOF
    pnts1|2001-01-01|2001-03-01
    pnts2|2001-05-01|2001-07-01
    EOF

    # Register the maps in new space time datasets
    t.create type=strds temporaltype=absolute output=A \
        title="A test with raster input files" descr="A test with raster input files"

    t.create type=stvds temporaltype=absolute output=P \
        title="A test with vector input files" descr="A test with vector input files"

    t.register type=raster -i input=A file="${n1}" start="2001-01-01" increment="1 months"

    # Raster map layer in A
    t.rast.list A

    name|mapset|start_time|end_time
    a1|PERMANENT|2001-01-01 00:00:00|2001-02-01 00:00:00
    a2|PERMANENT|2001-02-01 00:00:00|2001-03-01 00:00:00
    a3|PERMANENT|2001-03-01 00:00:00|2001-04-01 00:00:00
    a4|PERMANENT|2001-04-01 00:00:00|2001-05-01 00:00:00
    a5|PERMANENT|2001-05-01 00:00:00|2001-06-01 00:00:00
    a6|PERMANENT|2001-06-01 00:00:00|2001-07-01 00:00:00

    t.register type=vector input=P file="${n2}"

    # Vector map layer in P
    t.vect.list P

    name|layer|mapset|start_time|end_time
    pnts1|None|PERMANENT|2001-01-01 00:00:00|2001-03-01 00:00:00
    pnts2|None|PERMANENT|2001-05-01 00:00:00|2001-07-01 00:00:00

    # Start time of maps in A located in maps in P
    t.sample method=start input=A samtype=stvds sample=P -c

    P@PERMANENT|A@PERMANENT|start_time|end_time|interval_length|distance_from_begin
    pnts1@PERMANENT|a1@PERMANENT,a2@PERMANENT|2001-01-01 00:00:00|2001-03-01 00:00:00|59.0|0.0
    None|a3@PERMANENT,a4@PERMANENT|2001-03-01 00:00:00|2001-05-01 00:00:00|61.0|59.0
    pnts2@PERMANENT|a5@PERMANENT,a6@PERMANENT|2001-05-01 00:00:00|2001-07-01 00:00:00|61.0|120.0

    # P contains A
    t.sample method=contain input=A samtype=stvds sample=P -c

    P@PERMANENT|A@PERMANENT|start_time|end_time|interval_length|distance_from_begin
    pnts1@PERMANENT|a1@PERMANENT,a2@PERMANENT|2001-01-01 00:00:00|2001-03-01 00:00:00|59.0|0.0
    None|a3@PERMANENT,a4@PERMANENT|2001-03-01 00:00:00|2001-05-01 00:00:00|61.0|59.0
    pnts2@PERMANENT|a5@PERMANENT,a6@PERMANENT|2001-05-01 00:00:00|2001-07-01 00:00:00|61.0|120.0

    # A during P
    t.sample method=during intype=stvds input=P samtype=strds sample=A -c

    A@PERMANENT|P@PERMANENT|start_time|end_time|interval_length|distance_from_begin
    a1@PERMANENT|pnts1@PERMANENT|2001-01-01 00:00:00|2001-02-01 00:00:00|31.0|0.0
    a2@PERMANENT|pnts1@PERMANENT|2001-02-01 00:00:00|2001-03-01 00:00:00|28.0|31.0
    a3@PERMANENT|None|2001-03-01 00:00:00|2001-04-01 00:00:00|31.0|59.0
    a4@PERMANENT|None|2001-04-01 00:00:00|2001-05-01 00:00:00|30.0|90.0
    a5@PERMANENT|pnts2@PERMANENT|2001-05-01 00:00:00|2001-06-01 00:00:00|31.0|120.0
    a6@PERMANENT|pnts2@PERMANENT|2001-06-01 00:00:00|2001-07-01 00:00:00|30.0|151.0

    # No Overlapping
    t.sample method=overlap input=A samtype=stvds sample=P -cs

    P@PERMANENT|A@PERMANENT|start_time|end_time|interval_length|distance_from_begin
    pnts1@PERMANENT|None|2001-01-01 00:00:00|2001-03-01 00:00:00|59.0|0.0
    None|None|2001-03-01 00:00:00|2001-05-01 00:00:00|61.0|59.0
    pnts2@PERMANENT|None|2001-05-01 00:00:00|2001-07-01 00:00:00|61.0|120.0

    t.sample method=precedes input=A samtype=stvds sample=P -c

    P@PERMANENT|A@PERMANENT|start_time|end_time|interval_length|distance_from_begin
    pnts1@PERMANENT|a3@PERMANENT|2001-01-01 00:00:00|2001-03-01 00:00:00|59.0|0.0
    None|a5@PERMANENT|2001-03-01 00:00:00|2001-05-01 00:00:00|61.0|59.0
    pnts2@PERMANENT|None|2001-05-01 00:00:00|2001-07-01 00:00:00|61.0|120.0

    t.sample method=follows  input=A samtype=stvds sample=P -c

    P@PERMANENT|A@PERMANENT|start_time|end_time|interval_length|distance_from_begin
    pnts1@PERMANENT|None|2001-01-01 00:00:00|2001-03-01 00:00:00|59.0|0.0
    None|a2@PERMANENT|2001-03-01 00:00:00|2001-05-01 00:00:00|61.0|59.0
    pnts2@PERMANENT|a4@PERMANENT|2001-05-01 00:00:00|2001-07-01 00:00:00|61.0|120.0

    t.sample method=precedes,follows input=A samtype=stvds sample=P -c

    P@PERMANENT|A@PERMANENT|start_time|end_time|interval_length|distance_from_begin
    pnts1@PERMANENT|a3@PERMANENT|2001-01-01 00:00:00|2001-03-01 00:00:00|59.0|0.0
    None|a5@PERMANENT,a2@PERMANENT|2001-03-01 00:00:00|2001-05-01 00:00:00|61.0|59.0
    pnts2@PERMANENT|a4@PERMANENT|2001-05-01 00:00:00|2001-07-01 00:00:00|61.0|120.0

## SEE ALSO

t.create, t.info

## AUTHOR

Sören Gebbert, Thünen Institute of Climate-Smart Agriculture