The Moving surface operation is a point interpolation which requires a point map as input and returns a raster map as output. For each output pixel, a polynomial surface is calculated by a moving least squares fit; for each output pixel, the surface will approach the weighted point values of the points which fall within the specified limiting distance (see below). The calculated surface values are assigned to the output pixels.
The weight factors for the input points are calculated by a user-specified weight function. There are two methods: inverse distance and linear decrease. Both methods ensure that points which are close to an output pixel obtain large weights and that points which are farther away from an output pixel obtain small weights. The values of points which are close to an output pixel are thus of greater importance to the output value for that pixel than points which are farther away.
By specifying a limiting distance, you can influence until which distance from any output pixel, points will be taken into account for the calculation a value for that output pixel. For each output pixel, only the values of the points which fall within the limiting distance to this output pixel will be used to calculate a value for that output pixel. Values of points that are farther away from an output pixel than the specified limiting distance, obtain weight zero by the weight calculation, and these values will thus not be used in the output pixel value calculation. This speeds up the calculation and prevents artifacts.
The surfaces in this operation range from a simple plane to complex polynomial surfaces. You can usually select a first or second order surface, as these are the least sensitive to produce artificial extreme values.
For more information on weight calculation methods and surfaces, see Moving surface : algorithm.
Optionally, you can choose to calculate with spherical distances, i.e. distances calculated over the sphere using the projection that is specified in the coordinate system used by the georeference of the output raster map. It is advised to use this spherical distance option for maps that comprise large areas (countries or regions) and for maps that use LatLon coordinates. In more general terms, spherical distance should be used when there are 'large' scale differences within a map as a consequence of projecting the globe-shaped earth surface onto a plane.
When the spherical distance option is not used, distances will be calculated in a plane as Euclidean distances.
Input map requirements:
The input point map should be a value map. Furthermore, when a point map uses a class or ID domain and the map is linked to an attribute table, you can also use such a point map and select a column with a value domain from the map's attribute table.
Domain and georeference of output map:
The output raster map uses the same value domain as the input point map or the attribute column. The value range and precision can be adjusted for the output map. The georeference for the output map has to be selected or created; you can usually select an existing georeference corners.
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