Rasterio windows and masks

Sean Gillies

2013-12-21 00:00

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.