title: rasterio transform and affine
body: <p>Im trying to do some basic image filtering. Ive included a snippet verbatim from the rasterio cookbook (I removed .astype() from the median filter output). The issue is that my input and output rasters should have the same extent but dont. The transform and affine are different for the input and output. Is this the expected behavior? Do I need to do something to the affine and transform to get the output to be the same as the input?</p>
  
  <p>Python 2.7.11 |Anaconda 4.0.0 (64-bit)| (default, Feb 16 2016, 09:58:36) [MSC v.1500 64 bit (AMD64)] on win32</p>
  
  <p>rasterio==0.36.0</p>
  
  <pre><code>import rasterio
  from scipy.signal import medfilt
  
  path = "map.tif"
  output = "map2.tif"
  
  with rasterio.open(path) as src:
      array = src.read()
      profile = src.profile
  
  # apply a 5x5 median filter to each band
  filtered = medfilt(array, (1, 5, 5))
  
  # Write to tif, using the same profile as the source
  with rasterio.open(output, 'w', **profile) as dst:
      dst.write(filtered)
  
      print profile
      print dst.profile
  
  &gt;&gt;&gt; {'count': 1, 'crs': CRS({'init': u'epsg:3857'}), 'interleave': 'band', 'dtype': 'float64', 'affine': Affine(100.0, 0.0, -13250000.0, 0.0, 100.0, 3980000.0), 'driver': u'GTiff', 'transform': (-13250000.0, 100.0, 0.0, 3980000.0, 0.0, 100.0), 'height': 1700, 'width': 1700, 'tiled': False, 'nodata': None}
  &gt;&gt;&gt; {'count': 1, 'crs': CRS({'init': u'epsg:3857'}), u'interleave': 'band', 'dtype': 'float64', 'affine': Affine(-13250000.0, 100.0, 0.0, 3980000.0, 0.0, 100.0), 'driver': u'GTiff', 'transform': (0.0, -13250000.0, 100.0, 100.0, 3980000.0, 0.0), 'height': 1700, 'width': 1700, u'tiled': False, 'nodata': None}
  </code></pre>