I am trying to create a mosaic dataset that keeps the properties of the original rasters. However, when I try to use arcpy's MosaicToNewRaster, the nodata type of -999999.0 is not carried over. I would like to keep this default.

As a Minimum Reproducible Example, I am using the first three rasters on this page: https://rockyweb.usgs.gov/vdelivery/Datasets/Staged/Elevation/OPR/Projects/CO_NorthwestCO_2020_D20/CO_NWCO_1_2020/TIFF/

import arcpy
import os

directory_tiff = 'myPathToDownloadedTiffs'
string_raster_mosaic = 'Mosaic_Test.tif'

arcpy.env.workspace = directory_tiff
list_opr_tiles = arcpy.ListRasters()

rasInfo = arcpy.Raster(list_opr_tiles[0]).getRasterInfo()

pixel_types = {
    "U1": "1_BIT",
    "U2": "2_BIT",
    "U4": "4_BIT",
    "S8": "8_BIT_UNSIGNED",
    "U8": "8_BIT_SIGNED",
    "S16": "16_BIT_UNSIGNED",
    "U16": "16_BIT_SIGNED",
    "S32": "32_BIT_UNSIGNED",
    "U32": "32_BIT_SIGNED",
    "F32": "32_BIT_FLOAT",
    "F64": "64_BIT"

string_pixel_type = pixel_types[rasInfo.getPixelType()]

arcpy.MosaicToNewRaster_management(input_rasters = list_opr_tiles, output_location = directory_tiff, raster_dataset_name_with_extension = string_raster_mosaic, pixel_type = string_pixel_type, number_of_bands = 1)

The code above produces a mosaic, and recognizes nodata correctly, but the nodata value in properties changes to 3.4e+38.

I then tried adding an additional step to try to assign a no-data with SetRasterProperties. That changes the nodata property value to -999999.0, but changes actual no data values to 3.4e+38.

How can I use mosaic to new raster to create a mosaic honoring the original no data of -999999.0? I am trying to avoid copying the first raster and mosaicking the others to that copy because I have 7k+ rasters and may have to break up the tiles into groups to create sub-mosaics before combining those into a final mosaic.

  • 1
    Alternative method is to use osgeo.gdal.BuildVRT. The osgeo.gdal package is included in the base ArcGIS Pro python environment.
    – user2856
    Commented Jan 26 at 4:51
  • The mosaic tool honours nodata environment settings, try setting that?
    – Hornbydd
    Commented Jan 26 at 15:29
  • Thank you @Hornbydd. I did try arcpy.env.nodata = 'NONE' right before MosaicToNewRaster and the nodata value is still converted to 3.4e+38.
    – ENIAC-6
    Commented Jan 26 at 16:07

1 Answer 1


Thanks to user2856's comment, using gdal from my cloned arcgispro-py3 environment worked (code from: https://www.youtube.com/watch?v=sBBMKbAj8XE).

from osgeo import gdal
import glob, os

directory_tiff = 'myPathToDownloadedTiffs'
demList = glob.glob('*.tif')
vrt = gdal.BuildVRT('merged.vrt', demList)
gdal.Translate('mergedDEM2.tif', vrt)
vrt = None

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