# Rasterio windows and masks

Rasterio 0.4 is up on PyPI: https://pypi.python.org/pypi/rasterio/0.4. The new features since the last time I blogged about rasterio are windowed and masked reads and writes. Here's an example that combines both features and demonstrates a good pattern for reading raster data.

import numpy import rasterio with rasterio.open('rasterio/tests/data/RGB.byte.tif') as src: # The following asserts that all bands have the same block/stripe structure. assert len(set(src.block_shapes)) == 1 # As they do, we can iterate over the first band's block windows # and apply to all other bands. for ji, window in src.block_windows(1): # Get data in this window for each band as a Numpy masked array. bands = [ numpy.ma.masked_equal( src.read_band(src.indexes[i]), src.nodatavals[i]) for i in range(src.count)] # Break out after the first block in this example. break # Let's look at the first, blue band. b = bands[0] print(b) print(b.mask) print(b.fill_value) print(b.min(), b.max(), b.mean())

The output:

[[-- -- -- ..., -- -- --] [-- -- -- ..., -- -- --] [-- -- -- ..., -- -- --] ..., [-- -- -- ..., -- -- --] [-- -- -- ..., -- -- --] [-- -- -- ..., -- -- --]] [[ True True True ..., True True True] [ True True True ..., True True True] [ True True True ..., True True True] ..., [ True True True ..., True True True] [ True True True ..., True True True] [ True True True ..., True True True]] 0 (1, 255, 44.434478650699106)

You can see that all four corners of the test image are masked.