Collocation

Introduction

The Collocation Tool allows to collocate spatially overlapping products. Collocating products implies that the pixel values of slave products are resampled into the geographical raster of the master product.

In order to avoid naming conflicts, the Collocation Tool allows to rename both master and slave components such as bands, flag codings and bitmask definitions according to a user defined pattern.

Algorithm

When products are collocated, a new product is created which contains a copy of all components of the master product, i.e. band data, tie-point grids, flag codings, bitmask definitions, and metadata. The components of the slave products are transfered in a different manner:

The band data of the slave products are resampled into the geographical raster of the master product. The user may choose between three different resampling methods: Nearest Neighbour, Bilinear Interpolation, and Cubic Convolution. For flag bands and bands where a valid-pixel expression is defined, the Nearest Neighbour method is used. In order to establish a mapping between the samples in the master and the slave rasters, the geographical position of a master sample is used to find the corresponding sample in the slave raster. If there is no sample for a requested geographical position, the master sample is set to the no-data value which was defined for the slave band. The collocation algorithm requires accurate geopositioning information for both master and slave products. When necessary, accurate geopositioning information may be provided by ground control points.

As for the master product, the tie-point grids, flag codings and bitmask definitions of the slave products are copied. Slave product metadata are not transfered.

User Interfaces

The Collocation Tool can be invoked from the tool menu in the Sentinel Toolbox by selecting Processing->Geometric Operations->Collocation..., or in batch mode by using the command line tool gpt (Graph Processing Tool) which is located in the bin directory. For the latter type gpt Collocate -h for further information.

Selecting the Collocation... command from the Sentinel Toolbox tool menu pops up the following dialog:

Collocation Dialog

Source Products Group

Master: Here the user specifies the master product. The combo box presents a list of all products opened in the Sentinel Toolbox. The user may select one of these or, by clicking on the button next to the combo box, choose a product from the file system.

Slave: Here the user specifies the slave products. The user may select products opened in SNAP or products from the file system.

Target Product Group

Name: Used to specify the name of the target product.

Save to: Used to specify whether the target product should be saved to the file system. The combo box presents a list of file formats.

Open in SNAP: Used to specify whether the target product should be opened in the Sentinel Toolbox. When the target product is not saved, it is opened in the Sentinel Toolbox automatically.

Component Renaming Group

Each product consists of different components, such as bands, flag codings and bitmask definitions. In order to avoid naming conflicts between master and slave product components, the user can specify a renaming pattern.

Rename master components: By checking or unchecking this option the automatic renaming of master product components can be activated or deactivated, respectively. If activated, all components of the master product are renamed according to the pattern given in the text field next to the check box. The expression ${ORIGINAL_NAME} can be used to refer to the original name of the component.

Rename slave components: By checking or unchecking this option the automatic renaming of slave product components can be activated or deactivated, respectively. If activated, all components of the slave products are renamed according to the pattern given in the text field next to the check box. The expression ${ORIGINAL_NAME} or ${SLAVE_NUMBER_ID} can be used to refer to the original name of the component or the id of the slave (0,1,2...) respectively.

Resampling Group

Method: The combo box presents several resampling methods: Nearest Neighbour, Bilinear Interpolation, and Cubic Convolution. When the slave product contains a band where a valid-pixel expression is defined, only the Nearest Neighbour method is presented.