Merging raster TIFF with different values

arcgis-desktopgeotiff-tiffmergemosaicraster

I have 2 rasters (TIFF), 16 bit and with 1 band each. The first one showing 2 classes: (1) disturbance (value 1) and (2) no change (value 0). The second raster has 2 classes too: (1) recovery (value 2) and (2)no change(0).

I tried to merge them using mosaic to new raster in ArcGIS in order to get a raster with 3 values showing no change, disturbance, and recovery(value 0, value 1, and value 2). Instead of getting those 3 values, I get a raster with 2 values either 0 and 1 or 0 and 2.

Could anyone explain what is the problem and how to tackle it?

Best Answer

Mosaic to New Raster doesn't do what you think it does. It is for joining adjacent rasters with the same range of values into one single larger mosaiced raster.

You want to use the Raster Calculator to do a simple sum of your rasters (i.e. Expression = Raster1 + Raster2). This will give you an output with four potential values - 0 (no change, no change), 1 (disturbance, no change), 2 (recovery, no change), and 3 (disturbance, recovery).

Be sure to check you rasters have their cells aligned and are of the same size before you start. If not, check that the cell size environment settings are appropriate or consider changing the resolution of one of your rasters to match the other.

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[GIS] Understanding min and max values with Mosaic to New Raster

As whuber mentioned, often statistics found in the raster properties are sometimes approximate or are out-of-date. They are predetermined properties that can be misleading to the actual raster values.

Calculated your own min / max values from 100% of the actual data using NumPy arrays. See Working with NumPy in ArcGIS, and RasterToNumPyArray (arcpy). E.g.:

import arcpy

inrast = r'C:\data\inRaster.tif'
my_array = arcpy.RasterToNumPyArray(inrast)
print((my_array.min(), my_array.max()))

If you have missing values (NODATA) then a masked array is needed to get the correct stats:

import numpy as np
my_array = arcpy.RasterToNumPyArray(inrast)
my_masked_array = np.ma.masked_equal(my_array, arcpy.Raster(inrast).noDataValue)
print((my_masked_array.min(), my_masked_array.max()))

Also, you don't need ArcGIS to read rasters as NumPy arrays; e.g. GDAL or rasterio can do similar.

[GIS] What method does QGIS Merge Rasters tool use

For merging rasters, QGIS use the script gdal_merge (Python script)

gdal_merge.py raster1.tif raster2.tif raster3.tif -o merged.tif

Merge method is for the QGIS tool under Vector -> Miscellaneous -> Merge merge vector layers, as its name indicates

Best Answer

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[GIS] Understanding min and max values with Mosaic to New Raster

[GIS] What method does QGIS Merge Rasters tool use

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