r.gdd - GRASS GIS manual

NAME

r.gdd - Makes each output cell value a function of the values assigned to the corresponding cells in the input raster map layers.

KEYWORDS

raster, series

SYNOPSIS

r.gdd

r.gdd --help

r.gdd [-nz] [input=name[,name,...]] [add=name] [file=name] output=name [index=string] [scale=float] [shift=float] [baseline=float] [cutoff=float] [range=lo,hi] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

-n: Propagate NULLs
-z: Don't keep files open
--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:

input=name[,name,...]: Name of input raster map(s)
add=name: Existing map to be added to output
file=name: Input file with raster map names, one per line
output=name [required]: Name for output raster map
index=string: Index to calculate; Options: gdd, winkler, bedd, huglin; Default: gdd; gdd: Growing Degree Days; winkler: Winkler index; bedd: Biologically Effective Degree Days; huglin: Huglin Heliothermal index
scale=float: Scale factor for input; Default: 1.0
shift=float: Shift factor for input; Default: 0.0
baseline=float: Baseline temperature; Default: 10
cutoff=float: Cutoff temperature; Default: 30
range=lo,hi: Ignore values outside this range

DESCRIPTION
NOTES
EXAMPLES
SEE ALSO
AUTHOR

DESCRIPTION

r.gdd calculates (accumulated) growing degree days (GDDs), Winkler indices, Biologically Effective Degree Days (BEDD), and Huglin indices from several input maps with temperature data for different times of the day.

GDDs are calculated as

    gdd = average - baseline

The Winkler index is calculated as

    wi = average - baseline

usually accumulated for the period April 1^st to October 31^st (northern hemisphere) or the period October 1^st to April 30^th (southern hemisphere).

BEDDs are calculated as

    bedd = average - baseline

with an optional upper cutoff applied to the average. Vine development kinetics for example reach a plateau at an average daily temperature of 19°C.

The Huglin heliothermal index is calculated as

    hi = (average + max) / 2 - baseline

usually accumulated for the period April 1^st to September 30^th (northern hemisphere) or the period September 1^st to April 30^th (southern hemisphere).

Any averages above the cutoff value are set to cutoff, and any average values below the baseline value are set to baseline. Negative results are set to 0 (zero).

The shift and scale values are applied directly to the input values. The baseline, cutoff, and range options are applied to the shifted and scaled values.

If an existing map is provided with the add option, the values of this map are added to the output, thus accumulating the selected index.

NOTES

The scale and shift parameters are used to transform input values with

    new = old * scale + shift

With the -n flag, any cell for which any of the corresponding input cells are NULL is automatically set to NULL (NULL propagation) and the index is not calculated.

Without the -n flag, all non-NULL cells are used to calculate the selected index.

If the range= option is given, any values which fall outside that range will be treated as if they were NULL. Note that the range is applied to the scaled and shifted input data. The range parameter can be set to low,high thresholds: values outside of this range are treated as NULL (i.e., they will be ignored by most aggregates, or will cause the result to be NULL if -n is given). The low,high thresholds are floating point, so use -inf or inf for a single threshold (e.g., range=0,inf to ignore negative values, or range=-inf,-200.4 to ignore values above -200.4).

The number of raster maps to be processed is given by the limit of the operating system. For example, both the hard and soft limits are typically 1024. The soft limit can be changed with e.g. ulimit -n 1500 (UNIX-based operating systems) but not higher than the hard limit. If it is too low, you can as superuser add an entry in

/etc/security/limits.conf
# <domain>      <type>  <item>         <value>
your_username  hard    nofile          1500

This would raise the hard limit to 1500 file. Be warned that more files open need more RAM.

Use the file option to analyze large amount of raster maps without hitting open files limit and the size limit of command line arguments. The computation is slower than the input option method. For every sinlge row in the output map(s) all input maps are opened and closed. The amount of RAM will rise linear with the number of specified input maps. The input and file options are mutually exclusive. Input is a text file with a new line separated list of raster map names.

EXAMPLES

Example with MODIS Land Surface Temperature, transforming values from Kelvin * 50 to degrees Celsius:

r.gdd in=MOD11A1.Day,MOD11A1.Night,MYD11A1.Day,MYD11A1.Night out=MCD11A1.GDD \
      scale=0.02 shift=-273.15 baseline=10 cutoff=30

AUTHOR

Markus Metz (based on r.series)

SOURCE CODE

Available at: r.gdd source code (history)