In the illustration below, the cell centers of the input raster are the gray points. For each output cell, a value needs to be derived from the input raster. Since the output cell values remain the same, nearest neighbor assignment should be used for nominal or ordinal data, where each value represents a class, member, or classification (categorical data such as a land-use, soil, or forest type).Ĭonsider an output raster created from an input raster that is rotated 45° in an operation and thus will be resampled.
The value 2 in the input raster will always be the value 2 in the output raster it will never be 2.2 or 2.3. The nearest neighbor assignment does not change any of the values of cells from the input raster dataset. Once the location of the cell's center on the output raster dataset is located on the input raster, nearest neighbor assignment will determine the location of the closest cell center on the input raster and assign the value of that cell to the cell on the output raster. Nearest neighbor assignment is the resampling technique of choice for discrete (categorical) data since it does not alter the value of the input cells. Thus, the values assigned to the cells of an output raster may differ according to the technique used. Each of these techniques assigns values to the output differently. The three techniques for determining output values are nearest neighbor assignment, bilinear interpolation, and cubic convolution. Therefore, techniques have been developed to determine the output value depending on where the point falls relative to the center of cells of the input raster and the values associated with these cells. It is rare that an output cell center will align exactly with any cell center of the input raster. Once the input location is identified, a value can be assigned to the output location based on the nearby cells in the input. Each cell center coordinate is transformed backward to identify the location of the point on the original input raster. To find the value each cell should receive on the resampled output raster, the center of each cell in the output must be mapped to the original input coordinate system. Five-kilometer cells might be more applicable when studying the effects of global warming over the earth. For example, it is unlikely you will study mouse movement when the cell size is 5 kilometers. When performing analysis, make sure you are asking appropriate questions of the cell size. On execution, the input raster will first be resampled to the coarser resolution, then the tool is applied. In the image below, the cell size that was set in the analysis environment is coarser than the cell size of the input raster to the tool. Specifying a cell size of 50 meters when the input raster datasets have a resolution of 100 meters will create an output raster with a cell size of 50 meters however, the accuracy is still only 100 meters. The result is only as precise as the coarsest input. No new data is created cells are interpolated using nearest neighbor resampling.
Note:Įxercise caution when specifying a cell size finer than that of the input raster datasets. The bilinear and cubic techniques can be applied using the Resample tool as a pre-processing step before combining rasters of different resolutions. A resampling technique is necessary because rarely do the centers of the input cells align with the transformed cell centers of the desired resolution. This is because it is applicable to both discrete and continuous value types, while the other resampling types-bilinear interpolation and cubic convolution-are only applicable to continuous data.
In the default case, the nearest neighbor assignment resampling technique is used. When multiple raster datasets are input into any ArcGIS Spatial Analyst extension tool and their resolutions are different, one or more of the input datasets will be automatically resampled to the coarsest resolution of the input datasets. But when you are processing between multiple datasets, the cell resolution, like the registration, ideally should be the same. Different raster datasets do not need to be stored using the same cell resolution.
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