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FAQ: How is bilinear interpolation calculated?

Question

How is bilinear interpolation calculated?

Answer

Bilinear interpolation identifies the four nearest input cell centers to the location of the center of an output cell on the input grid. The new value for the output cell is a weighted average determined by the value of the four nearest input cell centers and their relative position or weighted distance from the location of the center of the output cell in the input grid.
[O-Image] Bilinear interpolation
Since the values for the output cells are calculated according to the relative position and the value of the input cells, the bilinear interpolation is preferred for data where the location from a known point of phenomenon determines the value assigned to the cell, i.e., continuous surfaces. Elevation, slope, intensity of noise from an airport, and salinity of the groundwater near an estuary are all phenomenon represented as continuous surfaces and are most appropriately resampled using bilinear interpolation.