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gvSIG-Desktop 1.9 Alpha. Manual de usuario.
Cálculo de Bandas
Descripción de la calculadora de bandas
Band calculator allows you to perform mathematical operations between band values of the same image or from different images maintaining some spatial constraints (always on original values). The result of this operation is a one-band raster image.
To open the Calculator tool, you have to use the remote sensing toolbar by selecting “Raster process” from the left button and “Raster calculator” from the right button.
- the elements tree: allows to add different elements to the operation just browsing and double click over the selected element.
- expression frame: expression used for the operation
- table of variables: will contain the relation between variables and bands
- calculator keyboard: allow to insert numerical values as well as basic operators in the expression.
Realizar un cálculo
To perform a calculation among bands, you have to introduce an expression in the expression frame and link one band of the raster layers loaded in the TOC to one of the variables listed in the expression.
Write the expression in the expression frame. To do that, you can use all the elements of the calculator.
The decision tree contains the raster layer bands, functions, operators and constants that can be used to compose the expression. Make double click on the chosen element to introduce it in the expression (in the position where the cursor is located). For the bands, you will introduce a varaible that will be automatically associated to the band in the variables table.
Use the keyboard of the calculator to introduce numbers, operators, parenthesis and decimal separator in the expression.
In the variables table you can establish the association between the variables present in the expression and the bands of the raster layer. To link one band to one variable, or to change a link, select the table and double click over the desired band in the decision tree.
Check the box “Allow different dimensions” if you want that the bands having different dimensions, position or pixel size will be part of the calculation. This option involve the use of interpolation to obtain a result.
The result of a calculation is a one band raster layer, of type double, that contain the result of the expression for the pixels presents in ALL the input bands and the “no-data” value for the others.
Opciones de salida
In this window you can select the options for the generation of the calculus result.
Name of the layer (1): Introduce the name of the raster layer that will be loaded in the window as calculus result.
Destination of the result (2): Select if you prefer to save the result as a file or to keep in memory. In the first case you will be asked for the path and the name of the file as the calculation will start. If you choose to keep in memory, you can save it later trough the option “Save as” by clicking with the right mouse button over the corresponding layer in the TOC.
Extension of the resulting raster (3). You can choose the extension and the cell size from the following possibilities:
1. Adjust to the input data: The extension of the resulting raster layer will be the union of the single band extensions presents in the calculation. The resulting cell size will be the smaller one amongst the bands presents in the calculation.
2. User defined: Use this option to introduce in the frame Parameters (4) maximum and minimum X and Y values and the output cell size.
3. Use other layer extension: The extension of the resulting layer will assume the ones of the selected raster layer.
Salvar y cargar expresiones
Click the button Save of the main control panel of the band calculator to save the expression shown in the Expression frame. A dialog window will appear to input the path and the name of the output file.
Click the button Load of the main control panel of the band calculator to an expression previously saved. The expression has to be saved as .exp
