20.2 Subtraction

This connection function performs a subtraction of the values within two or more files.NODATA values will be declared as NODATA values in the output file.

difference = minuend − subtrahend − subtrand  − ...− subtrahend .
                                1         2                 n

If only one subtrahend exists relative values can be calculated as a relative difference between the minuend and the subtrahend according to the formula

relativedifference = minuend-−-subtrahend

20.2.1 The Subtraction Settings Dialog

Figure 61Subtraction Properties Dialog

Select the minuend. All other files are automatically declared as subtrahends. Optionally selecte relative values. This option is only available if only one subtrahend exists.

NODATA values in the minuend file will result in the division by zero which would normally return an error. You can select from three different options for how to treat the cases of division by zero. The three options are:

  • Set NoDataValue: the output value will be NODATA
  • Set By Maximal Precision: the output value will be the smallest value above zero according to the specified precision values
  • Set Dummy Value: a dummy value will be assigned that can be specified in the value window