DESCRIPTION

t.rast.what.aggr samples a space time raster dataset at points from a vector map and returns aggregated values either printing them to stdout or updating the attribute table. A single date for the aggregation can be provided with the option date or alteratively, different dates for each point in the vector map can be passed through the option date_column. Either date or date_column must be provided. The aggregation is done by default backwards in time starting from the date provided and with the granularity set. Alternatively, the data can be aggregated forward in time by using the a flag. By default, the output is printed to stdout. To write the output into the attribute table of the vector map, u flag must be set and the target column should be created beforehand (See v.db.addcolumn). Alternatively, c flag creates the columns using the name of the space time raster dataset (strds) and the method(s) as column name(s).

NOTES

For method=mode the module requires scipy library to be installed.

EXAMPLES

Average NDVI for the previous 2 months starting from 2015-05-01 (i.e.: date="2015-05-01") for all points in the vector map. 
t.rast.what.aggr input=GR_GSOM_stations strds=ndvi_16_5600m \
 date=2015-05-01 granularity="2 months"

1|2015-05-01|4480.0
2|2015-05-01|5852.66666667
3|2015-05-01|5683.33333333
4|2015-05-01|4985.0
Average, minimum and maximum NDVI for the previous 2 months starting from 2015-05-01 (i.e.: date="2015-05-01") for all points in the vector map. 
t.rast.what.aggr input=GR_GSOM_stations strds=ndvi_16_5600m \
 date=2015-05-01 granularity="2 months" method=average,minimum,maximum

1|2015-05-01|4480.0|4371.0|4545.0
2|2015-05-01|5852.66666667|5618.0|6249.0
3|2015-05-01|5683.33333333|5530.0|5955.0
4|2015-05-01|4985.0|4820.0|5169.0
Average NDVI for the previous 2 months, starting from different dates for each point in the vector map (i.e.: providing date_column). 
t.rast.what.aggr input=GR_GSOM_stations strds=ndvi_16_5600m \
 granularity="2 months" date_column=fechas 

1|2015-01-01|*
2|2015-02-01|5254.0
3|2015-03-01|6023.66666667
4|2015-04-01|4399.66666667
Minimum and maximum NDVI for the previous 2 months, starting from different dates for each point in the vector map (i.e.: providing date_column). 
t.rast.what.aggr input=GR_GSOM_stations strds=ndvi_16_5600m \
 date_column=fechas granularity="2 months" \
 method=minimum,maximum
 
1|2015-01-01|*|*
2|2015-02-01|5254.0|5254.0
3|2015-03-01|5944.0|6119.0
4|2015-04-01|3786.0|4820.0
Minimum and maximum NDVI for the 2 months after (i.e.: set -a flag) the date provided in date_column. Note that in this example the first point gets populated. 
t.rast.what.aggr -a input=GR_GSOM_stations date_column=fechas \
 granularity="2 months" strds=ndvi_16_5600m method=minimum,maximum

1|2015-01-01|3497.0|4280.0
2|2015-02-01|4801.0|6249.0
3|2015-03-01|5530.0|5955.0
4|2015-04-01|5169.0|6390.0
Minimum and maximum NDVI for the previous 2 months, starting from different dates for each point in the vector map (i.e.: providing date_column) and write the output into the vector atrribute's table. 
# create columns
v.db.addcolumn map=GR_GSOM_stations column="ndvi_min double precision"
v.db.addcolumn map=GR_GSOM_stations column="ndvi_max double precision"

# write the aggregated values to the attribute table
t.rast.what.aggr -u input=GR_GSOM_stations strds=ndvi_16_5600m \
 date_column=fechas granularity="2 months" columns=ndvi_min,ndvi_max \
 method=minimum,maximum
 
# check the result
v.db.select map=GR_GSOM_stations

cat|station|name|long|lat|fechas|ndvi_min|ndvi_max
1|GRE00105244|LAMIA|22.4|38.9|2015-01-01||
2|GRE00105246|TANAGRA|23.53|38.32|2015-02-01|5254|5254
3|GRE00105240|CHIOS|26.13|38.33|2015-03-01|5944|6119
4|GRE00105242|FLORINA|21.4|40.78|2015-04-01|3786|4820
Automatically create the columns and populate them with the aggregated values. 
t.rast.what.aggr -u -c input=GR_GSOM_stations date_column=fechas \
 granularity="2 months" strds=ndvi_16_5600m method=minimum,maximum

v.db.select map=GR_GSOM_stations
cat|station|name|long|lat|fechas|ndvi_mean|ndvi_max|ndvi_16_5600m_minimum|ndvi_16_5600m_maximum
1|GRE00105244|LAMIA|22.4|38.9|2015-01-01||||
2|GRE00105246|TANAGRA|23.53|38.32|2015-02-01|5254|5254|5254|5254
3|GRE00105240|CHIOS|26.13|38.33|2015-03-01|5944|6119|5944|6119
4|GRE00105242|FLORINA|21.4|40.78|2015-04-01|3786|4820|3786|4820

SEE ALSO

r.what, t.rast.what, t.rast.aggregate

GRASS GIS Wiki: temporal data processing

AUTHOR

Luca Delucchi

Last changed: $Date$