aggregate raster using the most frequent value

Question

Does anyone have an idea how I could aggregate my raster so that in the output the most frequent value is used, as shown on the picture?

Answer 1

Here's an approach in R using the raster package:

x <-  c(
 1, 1, 1, 1, 1, 2, 4, 6, 7, 
 1, 3, 3, 2, 5, 6, 6, 7, 8, 
 1, 1, 3, 2, 2, 2, 4, 5, 6, 
 1, 2, 2, 2, 2, 4, 4, 6, 6, 
 1,NA, 1, 2, 2, 2, 4, 5, 6, 
 1,NA, 1, 2, 2, 3, 4, 5, 6, 
 1, 1, 1, 1, 1, 2, 3, 4, 5, 
 0, 0, 1, 1, 1, 2, 4, 4, 5, 
 0, 1, 1, 1, 1, 2, 3, 4, 4
 )

## build the raster object
library(raster)
r <- raster(matrix(x, ncol = 9, byrow = TRUE))

## aggregate by a factor of 3, with "modal"
m <- aggregate(r, fact = 3, fun = modal, na.rm = TRUE)

plot(m, addfun = function() text(m))

Answer 2

You're probably looking for something called "Majority Filter".

ArcGIS

You can use majority filtering also in the context of resampling a raster. In ArcGIS you will find the tool RESAMPLE in the Data Management Toolbox (check documentation).

Use this tool with "resampling_type" MAJORITY. Using this you can alter cell size for the target raster. The code in arcpy reads as follows:

arcpy.Resample_management("image.tif", "resample.tif", "10", "MAJORITY")

QGIS

For QGIS there are other options provided by the processing toolbox and SAGA/GRASS functions. Follow this link for further details.