assessType: Standardize type and determine associated no data value.

In ethanplunkett/rasterPrep: Package to prepare raster datasets for analysis or viewing

Standardize type and determine associated no data value.

Description

assessType standardize the storage type before passing it to GDAL and to determines the no data value to use for the storage type. It accepts type strings as used by gdal_translate and gdal_warp: "Byte", "Int16", "UInt16", "Int32", "UInt32", "Float32", "Float64"; or as used by terra::writeRaster(), standardizes them to work with gdal and returns the type, a logical indicating if it's a signed byte, and a no data value appropriate for that type.

Usage

assessType(type)

Arguments

type	A data type designation as used by gdalwarp and gdal_translate -ot arguments, or as used by the terra::writeRaster datatype argument.

Details

There is no universally accepted no data value for each type; every geoTIFF file can have it's own no data value. rasterPrep uses the highest possible value for unsigned integers, and lowest for signed integers. For floating point numbers it uses values close to the lowest possible. These follow the defaults used by the deprecated raster package, and for integers are consistent with terra::writeRaster() documentation.

SignedBytes are special case in GDAL and are written as bytes with an additional flag that indicates they are signed. I'm not sure how widely this is supported in other software. Although it is included here it is not currently supported by other rasterPrep functions.

Default No Data Values used in rasterPrep:

gdal	terra	No Data Value	Formula
SignedByte	INT1S	-1.280000e+02	-2^7
Byte	INT1U	2.550000e+02	2^8 -1
Int16	INT2S	-3.276700e+04	-2^15+1
UInt16	INT2U	6.553500e+04	2^16 - 1
Int32	INT4S	-2.147484e+09	-2^31+1
UInt32	INT4U	4.294967e+09	2^32-1
Float32	FLT4S	-3.400000e+38	-3.4E+38
Float64	FLT8S	-1.700000e+308	-1.7E+308

Value

assessType returns a list with:

type

(character) indicating the data type in the format used by gdal

isSignedByte

(logical) indicating if it should be written as a signed byte

noDataValue

(numeric) the value that will be used to represent no data in a raster of this type.

ethanplunkett/rasterPrep documentation built on Sept. 17, 2024, 1:05 p.m.