Pixel Extraction

Introduction

Basically, the Pixel Extraction Tool allows to extract the pixel values given by a user-specified list of geographic coordinates from a given list of data products. However, a number of additional parameters may be passed to the tool, for example the size of the area around the geographic coordinate which is to be considered.

Note that the Pixel Extraction Tool replaces the "Export Pin Pixels"-tool.

The Output Format

The Pixel Extraction Tool generates output in the widely used and very general CSV-format, using tabstops as separators.
It writes a file for each product type it has found within its input products (such as MER_FRS), each starting with a header looking like this:

# BEAM pixel extraction export table # # Window size: 1 # Expression: l1_flags.LAND_OCEAN # Created on: 2010-09-17 14:53:21
The header is followed by the table with the actual data; it might look like the following:

Expression result ProdID CoordID Name Latitude Longitude PixelX PixelY Date(yyyy-MM-dd) Time(HH:mm:ss) radiance_1 radiance_2

true 0 1 pin_1 41.31899 2.1386652 459.0 853.0 2003-08-09 12:14:16 157.6424 163.6796

true 1 1 pin_1 41.31899 2.1386652 459.0 853.0 2005-08-09 18:15:26 234.534 143.423

false 3 2 pin_2 43.3452 12.1232 539.0 533.0 2001-07-05 12:07:86 423.522194 156.625496

In the following table, the entries are explained in detail.

Field	Description
Expression result	True if the value matches the expression, false otherwise. Is omitted when expression is used for filtering.
ProdID	An ID for the product with relevance within the extracted data.
CoordID	An ID for the coordinate with relevance within the extracted data.
Name	The coordinate's name, if available.
Latitude	The coordinate's latitude value.
Longitude	The coordinate's longitude value.
PixelX	The data product's pixel value in x direction corresponding to the latitude value.
PixelY	The data product's pixel value in y direction corresponding to the longitude value.
Date(yyyy-MM-dd)	The data product's sensing date.
Time(HH:mm:ss)	The data product's sensing time.
radiance_1	Exemplarily: the first of the bands considered for value extracting.
radiance_2	Exemplarily: the second of the bands considered for value extracting.

The User Interface

The user interface of the Pixel Extraction Tool mainly consists of the Input/Output-pane and the Parameters-pane, as well as three buttons to start the extraction process, close the dialog, and open this help.

The Input/Output Pane

The Input/Output Pane allows to specify the input products and the output mode.

The Input/Output Pane

Input paths: The list contains the data products already chosen for extraction as well as paths to be searched for data products. Using the plusbutton -Button, data products can be added to the list in multiple ways:

by choosing a product already opened in VISAT
by choosing a product from the file system
by specifying a directory
or by specifying a directory recursively (indicated by '**' in the list)

Output directory: All output is written to the selected directory.

File prefix: The specified file prefix is used to prefix the files which are written.

The Parameters Pane

The Parameters Pane allows to specify several parameters used for the extraction.

The Parameters Pane

Coordinates: The coordinates table shows the user-specified geographic coordinates which are used to extract the values. They consist of a name and their latitude/longitude-values. Initially, the table is filled with the pins of the product currently selected in VISAT. Additional coordinates may be added either by creating new coordinates or by reading them from a pin file.
Additionally to the standard format of a pin file, the coordinates file file can have a 'DateTime' column. The format of the time value follows the ISO8601 pattern: yyyy-MM-dd'T'HH:mm:ss

Allowed time difference: Specifies how big the difference might be between the time at the pixel and the time of the coordinate.

Export: Specifies if bands, tie-point grids and/or masks should be included in the output.

Window size: The window size specifies the number of pixels surrounding the pixels derived from the given geographic coordinates to be exported. That is, when setting the window size to 3, the values for 9 pixels will be extracted. The window size must be odd.

Expression: A band maths expression can be specified to filter the values to output. The "Edit Expression..."-button opens the expression editor, which can be used for easily editing an expression. It is only available if the input product list of the "Input/Output"-pane contains at least one data product; however, in any case an expression may manually be declared.
There are two options of how to use the expression: either the expression is used to filter the values to output, that is, values which do not satisfy the expression are ignored. In the other case, the information if the value met the expression is added to the output.

Sub-scenes: Enables the export of sub-scenes. The scenes contain at least all coordinates (including the specified window) found in one product. Additionally the size of a border can be specified by which the exported scene size extended.

KMZ coordinates: All coordinates considered for the output are collected in one KMZ file. Which can be used to display the coordinates in Google Earth.