Get Default NoData Value for GeoPackage Raster Datatypes

Source: R/gpkg-util.R

Returns a default NoData value for a given raster datatype, following GDAL and terra conventions, and avoiding NaN values which produce a warning when passed as data_null to GDAL. NOTE: at this time (GDAL 3.12) only Byte (INT1U), Int16 (INT2S), UInt16 (INT2U) or Float32 (INT4S) datatypes are supported in the GPKG raster driver.

gpkg_default_nodata(datatype)

Arguments

datatype

character. A raster datatype code in terra format. Supported types are:

  • Signed integers: "INT1S", "INT2S", "INT4S", "INT8S"

  • Unsigned integers: "INT1U", "INT2U", "INT4U", "INT8U"

  • Floats: "FLT4S" (single precision), "FLT8S" (double precision)

Value

numeric. The default NoData value for the given datatype, or NA_real_ if no default is available or the datatype is not recognized.

Details

While NaN is technically a valid value for grids stored in a geopackage, it is generally prefered to use a numeric value, as NaN is not supported by SQLite 3 and is stored in the metadata column as SQL NULL. These defaults are used by gpkg_write() when auto_nodata = TRUE.

For signed integer types, the minimum representable value (e.g., INT32_MIN) is returned, as it is unlikely to occur in valid data. For unsigned integer types, the maximum representable value is returned (e.g., UINT16_MAX), with the exception of INT1U (byte) which returns 255 (following terra convention). For float types, the negative extreme value is returned, as GeoPackage metadata cannot represent NaN.

DatatypeDefault NoData
INT1S-128
INT2S-32768
INT4S-2147483648
INT8S-9223372036854775808
INT1U255
INT2U65534
INT4U4294967295
INT8U18446744073709549568
FLT4S-3.40282346638528860e+38
FLT8S-1.79769313486231571e+308

Note: The INT8U default (18446744073709549568) is UINT64_MAX - 1101 to account for floating-point precision loss when converting to double, following terra's convention. R does not have a native unsigned 64-bit integer type.

See also

gpkg_write() for using these defaults when writing rasters to GeoPackage

Examples

gpkg_default_nodata("FLT4S")
#> [1] -3.402823e+38
gpkg_default_nodata("INT2S")
#> [1] -32768
gpkg_default_nodata("INT2U") 
#> [1] 65535