The **-d** option
^^^^^^^^^^^^^^^^^

**Syntax**

**-di**\|\ **o**\ *nodata*\ [**+c**\ *col*]
    Substitute specific values with NaN.

**Description**

The **-d** option allows user-coded missing data values to be translated to official NaN values in GMT. Within GMT,
any missing values are represented by the IEEE NaN value. However, user data may occasionally denote missing data with
an unlikely value (e.g., -99999). Since GMT cannot guess this special missing data value, you can use the **-d**
option to have such values replaced with NaNs. Similarly, the **-d** option can replace all NaNs with the chosen
*nodata* value should the GMT output need to conform to such a requirement.

For input only, use **-di**\ *nodata* to examine all input columns after the first two. If any item equals *nodata*,
the value is interpreted as a missing data item and is substituted with the value NaN.

For output only, use **-do**\ *nodata* to examine all output columns. If any item equals NaN, the NaN value is
substituted with the chosen missing data value *nodata*.

Use the **+c** modifier to override the starting column used for the examinations [2 for input, 0 for output].