DFDX filter

The DFDX filter is a standard linear filter which works in a 1 by 5 environment. It calculates the first derivative in x-direction (df/dx) per pixel. The values in the matrix are:

Gain factor = 1/12 = 0.0833333

When using the DFDX filter on a DEM:

• positive values in the output map mean that the terrain goes up from left to right (West to East);
• negative values in the output map mean the terrain goes down.

Tip:

To find the real first derivative (per meter), the output values have to be divided by the pixel size of the map. You can use the MapCalc expression:

See also:

Filter types : linear filters

Filter types: gradient or derivative filters (technical information)

Filters : user-defined linear filters