[GIS] Mosaic To New Raster – Raster Cells Shift

arcgis-desktopmergemosaicraster

I have wind raster datasets for the U.S. that are organized by state and I would like to merge these datasets to get one map of the whole U.S.

I am new to using ArcGIS and through some research I found out that I can do this with the Mosaic To New Raster tool.

The problem that I'm running into is that even though I use the same projection, the raster cells seem to "shift" after having merged them. This can be seen in the pictures I uploaded!

Border of New Hampshire and Maine Original

What seems to be the problem here?
Is the Mosaic To New Raster tool the right choice?
I used "BLEND" as the mosaic operator.

Best Answer

As you can see on your first picture, the two raster aren't completely aligned. There are little white gaps where the two rasters meet. They will have to be resampled to fit together into one big raster and it is the result of this that causes the shift that you see in the second illustration.
The resampling is done when the 'Mosaic To New Raster'-tool runs.

You should be careful with this, as your datasets cover a large area, and they may have varying projections, which can cause problems when mosaicing.

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I recommend creating a mosaic dataset within a file geodatabase. There are many advantages of working with this type of data model. For one, you can modify properties of the dataset once it is created to enhance rendering. You also have much finer control of how these data are served compared to a stand-alone raster dataset created using mosaic to new raster.

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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As whuber mentioned, often statistics found in the raster properties are sometimes approximate or are out-of-date.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.

Best Answer

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