TASSEL

Description

TASSEL calculates the tasseled-cap transformation for the sensor and bands you specify.

Parameters

tassel(fili, visirchn, filo, datatype, scaloffs, scalfact, ftype, foptions)

Name	Type	Caption	Length	Value range
FILI *	str	Name of input file	1 -
VISIRCHN	List[int]	Required bands to calculate tasseled cap	0 - 6
FILO *	str	Name of the output file	1 -
DATATYPE	str	Output raster type	0 - 3	8U | 16S | 16U | 32R Default: 16S
SCALOFFS	List[float]	Scaling offset	0 - 3
SCALFACT	List[float]	Scaling factor	0 - 3
FTYPE	str	Format of output file	0 - 4	Default: PIX
FOPTIONS	str	Options for output format	0 -

* Required parameter

Parameter descriptions

FILI

The name of the input PCIDSK file.

The file must contain the specific bands necessary to calculate the tasseled-cap transformation. The number of bands in the file must range from three through six (Blue/Green/Red/NIR/SWIR1.6/SWIR2.2).

VISIRCHN

The bands required to calculate the tasseled-cap transformation.

You must specify each required band for each sensor in a specific order to ensure that the tasseled cap is computed correctly.

If you do not specify a value, the required bands are determined based on the metadata of the input file. The file metadata must have the necessary band information.

For example, consider a Landsat-8 sensor with the following band designations:

In such a case, enter the value as 3,4,2,1,5,6.

If a required band for a sensor is missing, the tasseled-cap transformation cannot be calculated.

If you do not specify a value, the band information is read from the metadata of the input file and based on wavelength.

FILO

The name of the output file to which to write the processed data.

The output file must not exist. The output file will be created based on the type specified for FTYPE and the options specified for FOPTIONS. The file will have the three output channels: brightness, greenness, and wetness. The type of output channel will be that specified for DATATYPE and have the same geocoding information and metadata as the input file.

DATATYPE

The data type of the output channel to create. When the output is written to existing channels, this parameter is ignored.

When the number of output channels is greater than one, the specified data type is used for each output channel.

The default value is 16S.

This parameter is optional.

SCALOFFS

Specifies the scaling offset used for converting the computed values to Digital Numbers (DNs) for storage in the output image.

A separate scaling offset for each output channel may be provided as a comma-separated list. (Brightness, Greenness, Wetness)

The target pixel-value range, after scaling, is as shown in the following table.

This parameter is optional.

If the scaling offset is specified, the scaling factor parameter must be specified as well.

These parameters are used jointly to convert the computed values to DNs as follows:

                            DN = Reflectance * Scaling factor + Scaling offset
               

Note: the radiometric gain and bias values stored in channel metadata are mutually related to the scaling factor and scaling offset values as follows:

                            Gain = Gain = 1 / Scaling factor
                            Bias = -Scaling offset / Scaling factor

                            Scaling factor = 1 / Gain
                            Scaling offset = -Bias / Gain
              

The default scaling offset and factor values for brightness, greenness, and wetness are as shown in the following table.

This parameter is optional.

SCALFACT

Specifies the scaling factor for converting the computed tasseled-cap values to Digital Numbers (DNs) for storage in the output image.

A separate scaling factor for each output channel may be provided as a comma-separated list. (Brightness, Greenness, Wetness).

If the Scaling factor is specified, the Scaling offset must be specified as well.

This parameter is optional.

Please refer to the Scaling offset parameter for more details, and for the list of data type-dependent default values.

FTYPE

The format of the output file.

The default value is PIX.

FOPTIONS

The options specific to the format to apply when creating the output file. With each, the default of no options is allowed (empty string).

Typically, the available options for a format include a compression scheme, format subtype, or other information.

Details

To calculate the tasseled-cap transformation, the input file must contain the specific bands necessary. The number of bands in the file must range from three through six (Blue/Green/Red/NIR/SWIR1.6/SWIR2.2). You must also specify the necessary bands (channels) in the correct order.

The output will always be three channels: brightness, greenness, and wetness.

The tasseled-cap transformation for brightness is written to the first output channel, greenness to the second channel, and wetness to the third channel of the output file.

Example

In the following example, a tasseled-cap transformation is applied to Landsat-8 data with linear scaling.

from pci.tassel import tassel

fili = 'AtcorCorr_landsat8.pix'
visirchn = []
filo = 'Tassel_landsat8.pix'
ftype = ''
foptions =''
scaloffs = []
scalfact = []
datatype= '16S'

tassel(fili, visirchn, filo, datatype, scaloffs, scalfact, ftype, foptions)