Array written by GDAL with Python script has numbers read as "nan" by QGIS?

Question

I would like to write an array to a geotiff with Python script using the GDAL module. When I try to do something simple like copying an existing GeoTiff via reading it to an array, then, writing to a new array, QGIS reads the integer value 1 as "nan". I have verified that the actual values that QGIS presents as "nan" are the integer value 1 in the GeoTiff. Is there some additional information that I need to write to the GeoTiff file so that QGIS will read my integer values of 1 as 1? My code is copied below:

import os
import gdal
os.chdir(r'C:\Users\pipi\Documents\Rogaine\Tarlo\gpx')

in_ds = gdal.Open('0011aa0011aa.tif')
in_band = in_ds.GetRasterBand(1)
noData = in_band.GetNoDataValue()
if noData:
    pass
else:
    noData = 0

cols = in_band.XSize
rows = in_band.YSize

# Creates an output file with the same dimensions and data type.
out_ds = gdal.GetDriverByName('GTiff').Create(
'master.tif', cols, rows, 1, gdal.GDT_Byte)
out_ds.SetProjection(in_ds.GetProjection())
out_ds.SetGeoTransform(in_ds.GetGeoTransform())
out_band = out_ds.GetRasterBand(1)

data = in_band.ReadAsArray()
out_band.WriteArray(data)
out_band.SetNoDataValue(noData)

del out_ds

Answer 1

There is no fault in the data or python script. QGIS's default for opening a raster dataset looks for a minimum and maximum value to provide band rendering. However, this dataset contains a single value. Within QGIS's layer properties style menu by setting both the Min and Max values of the dataset to the single dataset value and selecting "No enhancement" one can obtain a plot with a suitable legend.

Answer 2

Please try to set array nan's to your no data value before writing to band.

import numpy
...
data = in_band.ReadAsArray()

data[data==numpy.nan] = noData

out_band.WriteArray(data)
...

If the first dataset do not have a no data value set, set it first.