Band Maths Expression Editor

The Band Maths Expression Editor

VISAT's expression editor provides a convenient way to construct maths expressions with C syntax from various data sources, such as bands, tie-point grids and flag values. You can combine these data sources by a number of comparison, arithmetic, logical and binary operators or use them as arguments for mathematical functions.

Product:

Selects the current input product providing source bands, tie-point grids and flags. This selector is only shown if there is more than one compatible product.
If there is more than one input product available the references to bands and tie-points need to be prepended by a dollar and the reference number of the corresponding product separated by a dot.
The reference number of a product is the number in square brackets at the beginning of the product name. An expression pointing to a band called band_1 would than e.g. be $2.band_1.

Data Sources:

The list of available data sources provided by the selected input product. Click on a data source to move it into the expression text field.

Show bands checkbox
Checks whether or not the bands of a product are shown in the list of available data sources. References to bands in an expression always evaluate to geo-physical, scaled (calibrated) sample values.
If you are more interested in the raw sample values rather than the geo-physical sample values, use the syntax band.raw, where band is the name of any band.

Show masks checkbox
Checks whether or not the masks of a product are shown in the list of available data sources.

Show tie-point grids checkbox
Checks whether or not the tie-point grids of a product are shown in the list of available data sources.

Show single Flags checkbox
Checks whether or not the flags of a product are shown in the list of available data sources.

Expression:

The expression text field. You can also directly edit the expression here.

	Select All Button	Selects the entire text in the expression text field.
	Clear Button	Clears the entire text in the expression text field.
	Undo Button	Undoes multiple last edits in the expression text field.
	History Back Button	Lets you go back through history of expressions.
	History Forward Button	Lets you go forward through history of expressions.

OK Button

Accepts the expression.

Supported Operators and Functions

Important note: The operators listed here are enumerated in decreasing operator precendence (or increasing operator priority). If not otherwise stated, binary operators always bind (and evaluate) from left to right, so that A - B - C - D is equivalent to ((A - B) - C) - D.

This operator returns a value depending on a given boolean expression X.

These operators are provided to be used in conjunction with a data product's quality flags. The arguments must always be boolean.

These operators return boolean values true or false. You can use the conditional operator to convert the boolean return value into a real number, for example (radiance_13 <= 0) ? 0 : 10*sqrt(radiance_13)