i.hyper.specresamp

Spectral resampling of hyperspectral imagery.

Command linePython (grass.tools)Python (grass.script)

i.hyper.specresamp [-iv] input=name [reference=name] output=name [method=string] [wavelengths=string] [fwhm=string] [--overwrite] [--verbose] [--quiet] [--qq] [--ui]

Example:

i.hyper.specresamp input=name output=name

grass.tools.Tools.i_hyper_specresamp(input, reference=None, output, method="gaussian", wavelengths=None, fwhm=None, flags=None, overwrite=None, verbose=None, quiet=None, superquiet=None)

Example:

tools = Tools()
tools.i_hyper_specresamp(input="name", output="name")

This grass.tools API is experimental in version 8.5 and expected to be stable in version 8.6.

grass.script.run_command("i.hyper.specresamp", input, reference=None, output, method="gaussian", wavelengths=None, fwhm=None, flags=None, overwrite=None, verbose=None, quiet=None, superquiet=None)

Example:

gs.run_command("i.hyper.specresamp", input="name", output="name")

Parameters

Command linePython (grass.tools)Python (grass.script)

input=name [required]
    Input hyperspectral 3D raster map
reference=name
    Reference 3D raster map (reads target wavelengths from its metadata)
output=name [required]
    Output resampled 3D raster map
method=string
    Resampling method
    Allowed values: gaussian, linear, nearest
    Default: gaussian
wavelengths=string
    Output wavelength ranges (e.g. 400-700,700-2500) or explicit comma-separated values
fwhm=string
    FWHM (nm) per range for Gaussian (e.g. 8.3,11.5). Also sets band spacing within range.
-i
    Print resampling plan and exit (info mode)
-v
    Use only valid bands from input metadata
--overwrite
    Allow output files to overwrite existing files
--help
    Print usage summary
--verbose
    Verbose module output
--quiet
    Quiet module output
--qq
    Very quiet module output
--ui
    Force launching GUI dialog

input : str, required
    Input hyperspectral 3D raster map
    Used as: input, raster_3d, name
reference : str, optional
    Reference 3D raster map (reads target wavelengths from its metadata)
    Used as: input, raster_3d, name
output : str, required
    Output resampled 3D raster map
    Used as: output, raster_3d, name
method : str, optional
    Resampling method
    Allowed values: gaussian, linear, nearest
    Default: gaussian
wavelengths : str, optional
    Output wavelength ranges (e.g. 400-700,700-2500) or explicit comma-separated values
fwhm : str, optional
    FWHM (nm) per range for Gaussian (e.g. 8.3,11.5). Also sets band spacing within range.
flags : str, optional
    Allowed values: i, v
    i
        Print resampling plan and exit (info mode)
    v
        Use only valid bands from input metadata
overwrite : bool, optional
    Allow output files to overwrite existing files
    Default: None
verbose : bool, optional
    Verbose module output
    Default: None
quiet : bool, optional
    Quiet module output
    Default: None
superquiet : bool, optional
    Very quiet module output
    Default: None

Returns:

result : grass.tools.support.ToolResult | None
If the tool produces text as standard output, a ToolResult object will be returned. Otherwise, None will be returned.

Raises:

grass.tools.ToolError: When the tool ended with an error.

input : str, required
    Input hyperspectral 3D raster map
    Used as: input, raster_3d, name
reference : str, optional
    Reference 3D raster map (reads target wavelengths from its metadata)
    Used as: input, raster_3d, name
output : str, required
    Output resampled 3D raster map
    Used as: output, raster_3d, name
method : str, optional
    Resampling method
    Allowed values: gaussian, linear, nearest
    Default: gaussian
wavelengths : str, optional
    Output wavelength ranges (e.g. 400-700,700-2500) or explicit comma-separated values
fwhm : str, optional
    FWHM (nm) per range for Gaussian (e.g. 8.3,11.5). Also sets band spacing within range.
flags : str, optional
    Allowed values: i, v
    i
        Print resampling plan and exit (info mode)
    v
        Use only valid bands from input metadata
overwrite : bool, optional
    Allow output files to overwrite existing files
    Default: None
verbose : bool, optional
    Verbose module output
    Default: None
quiet : bool, optional
    Quiet module output
    Default: None
superquiet : bool, optional
    Very quiet module output
    Default: None

DESCRIPTION

i.hyper.specresamp performs spectral resampling of a hyperspectral 3D raster map (raster_3d). The module takes a hyperspectral cube imported with i.hyper.import and produces a new 3D raster whose spectral bands are arranged on a user-defined wavelength grid.

This is useful when harmonizing data from different sensors with different spectral sampling, or when simulating a multispectral sensor from hyperspectral data.

METHODS

Three resampling methods are available:

Gaussian convolution (default)

Each output band is computed as a weighted average of input bands based on a Gaussian spectral response function (SRF) centered on the target wavelength. The width of the Gaussian is controlled by the FWHM parameter (Schlapfer et al. 1999). This approach is physically motivated and best suited for sensor simulation or when spectral response fidelity is important.

Linear interpolation

A fast method where each output band is linearly interpolated between the two nearest input bands. This produces a smooth spectral curve and is appropriate when speed is preferred over exact response function matching.

Nearest neighbour

Each output band takes the value of the input band whose center wavelength is closest to the target. Useful for quick band thinning or band selection without any spectral mixing.

NOTES

No extrapolation: Output wavelengths are strictly limited to the spectral range of the input raster. Any target wavelength outside the input range is silently omitted. To resample to a wider spectral range, ensure the input raster covers the desired output range.

For example, when resampling EnMAP (418.4-2445.3 nm) to PRISMA (407.0-2497.1 nm), PRISMA bands below 418.4 nm or above 2445.3 nm will be omitted from the output.

When using the -v flag, bands marked as invalid in the input metadata (e.g., strong water vapor absorption or sensor artifacts) are excluded from the resampling.
The -i flag prints a resampling plan showing input/output band counts, spectral ranges, method, and FWHM parameters without executing the resampling.

EXAMPLES

Resample PRISMA to EnMAP spectral configuration using a reference raster

i.hyper.specresamp input=prisma@PERMANENT reference=enmap@PERMANENT \
    output=prisma_enmap_gauss method=gaussian -v

Resample using custom uniform wavelength ranges

i.hyper.specresamp input=prisma output=prisma_resampled \
    wavelengths=400-700,700-2500 fwhm=8.3,11.5 method=gaussian

This generates bands on a uniform grid with step = FWHM per range (e.g., 400-700 nm with 8.3 nm spacing, 700-2500 nm with 11.5 nm spacing). These FWHM values are typical of the EnMAP sensor (VNIR ~8.3 nm, SWIR ~11.5 nm).

Print resampling plan without executing

i.hyper.specresamp input=prisma reference=enmap -i -v

Example: Linear interpolation

i.hyper.specresamp input=prisma reference=enmap \
    output=prisma_enmap_linear method=linear

Example: Nearest neighbour

i.hyper.specresamp input=prisma reference=enmap \
    output=prisma_enmap_near method=nearest

SOURCE CODE

Available at: i.hyper.specresamp source code (history)
Latest change: Wednesday Sep 16 14:49:52 2026 in commit 9b0a4cb