Resample

Functionality

The Resample operation resamples a raster map from the map's current georeference to another target georeference. The coordinate of each output pixel is used to calculate a new value from close-by pixel values in the input map. Three resampling methods are available: nearest neighbour, bilinear interpolation, and bicubic interpolation.

In raster operations (e.g. MapCalc, Cross), all input raster maps must have the same georeference. Thus, prior to such operations, use Resample:

Tip:

It is not advisable to use Resample to make a raster map with any georeference use a georeference 3D; use the Apply 3D operation instead.

  

For more information on georeference types or on creating georeferences, refer to ILWIS objects : georeferences or How to create a georeference. For more information on editing a georef tiepoints, a georef direct linear or a georef orthophoto, refer to Tiepoint editor.

Resampling methods:

To resample an image, select an input image which has a georeference (usually a georeference tiepoints), select a resampling method (nearest neighbour, bilinear, bicubic), type an output map name and select the target georeference (usually a georeference corners).

For more information, see Resample : algorithm.

  

Fig. 1: Nearest neighbour resampling. Input pixels are represented by dashed black lines, coordinates of input pixels by black dots; output pixels are represented by red solid lines, coordinates of output pixels by red plus signs. The grey arrows indicate how output values are determined.

As you can see in Figure 1, some values of the input map may be used twice in the output map, while other input values may not be used at all.

  

Fig. 2: Bilinear resampling. Input pixels are represented by dashed black lines, coordinates of input pixels by black dots; output pixels are represented by solid red lines, coordinates of output pixels by red plus signs. The grey arrows indicate how output values are determined.

Input map requirements:

The input map needs to have a georeference; this is usually a georef tiepoints, a georef direct linear or a georef orthophoto.

Furthermore:

The operation can also be applied on all raster maps in a map list.

Domain and georeference of output map:

The output map uses the same domain as the input map. If the input map has a value domain, the value range and precision can be adjusted for the output map.

The target georeference for the output map has to be selected or created. You can usually select an existing georeference corners.

When the operation is performed on an input map list, you will obtain an output map list. When the output map list is opened, the output raster maps will be (defined and) calculated.

See also: