title: Access column with in another column header
body: <p>I opened a .mat file in python. I can see that there is one main column named 'CloudData' within the CloudData there are two columns 'Points' and 'RGB'. I can access the Points columns by using:</p>
  
  <pre><code>points_data=(data['CloudData']['Points'][0:1])
  </code></pre>
  
  <p>where data is the name of the file read in python using scipy.io. But when i try to read the data values, which is inside RGB as below:</p>
  
  <pre><code>channel_data=(data['RGB']['data_values']) 
  </code></pre>
  
  <p>I get the error complaining:
  KeyError: 'RGB'</p>
  
  <p>Is there any consideration to be taken after opening .mat file in python?
  Actually in the Matlab, the variable data_values is displayed with CloudData.RGB.data_values as title on the variable viewer window.</p>
  
  <p>For the first step, i want to read the values inside the RGB header, which is inside CloudData. </p>