title: GDAL ReadAsArray() returns just nan values when trying to read ENVI file
body: <p>I am trying to read an ENVI file as an array using GDAL and Python</p>
  
  <p>Image info are following:</p>
  
  <pre><code>Driver: ENVI/ENVI .hdr Labelled
  Files: IMG-VV-ALPSRP248213250-P1.1__D_pwr_geo_sigma
       IMG-VV-ALPSRP248213250-P1.1__D_pwr_geo_sigma.hdr
  Size is 1659, 2775
  Coordinate System is:
  PROJCS["UTM Zone 16, Northern Hemisphere",
      GEOGCS["WGS 84",
          DATUM["WGS_1984",
          SPHEROID["WGS 84",6378137,298.257223563,
              AUTHORITY["EPSG","7030"]],
          TOWGS84[0,0,0,0,0,0,0],
          AUTHORITY["EPSG","6326"]],
      PRIMEM["Greenwich",0,
          AUTHORITY["EPSG","8901"]],
      UNIT["degree",0.0174532925199433,
          AUTHORITY["EPSG","9108"]],
      AUTHORITY["EPSG","4326"]],
  PROJECTION["Transverse_Mercator"],
  PARAMETER["latitude_of_origin",0],
  PARAMETER["central_meridian",-87],
  PARAMETER["scale_factor",0.9996],
  PARAMETER["false_easting",500000],
  PARAMETER["false_northing",0],
  UNIT["Meter",1]]
  Origin = (332125.000000000000000,2017650.000000000000000)
  Pixel Size = (25.000000000000000,-25.000000000000000)
  Image Structure Metadata:
    INTERLEAVE=PIXEL
  Corner Coordinates:
  Upper Left  (  332125.000, 2017650.000) ( 88d35'16.06"W, 18d14'29.96"N)
  Lower Left  (  332125.000, 1948275.000) ( 88d34'55.98"W, 17d36'53.41"N)
  Upper Right (  373600.000, 2017650.000) ( 88d11'44.12"W, 18d14'40.22"N)
  Lower Right (  373600.000, 1948275.000) ( 88d11'29.00"W, 17d37' 3.30"N)
  Center      (  352862.500, 1982962.500) ( 88d23'21.23"W, 17d55'47.10"N)
  Band 1 Block=1659x1 Type=Float32, ColorInterp=Undefined
  </code></pre>
  
  <p>My code is the following:</p>
  
  <pre><code>driver = gdal.GetDriverByName('ENVI')
  driver.Register()
  
  #Mind the suffix (It is an ENVI file)    
  file = 'C:/img.1__A_pwr_geo_sigma
  
  raster = gdal.Open(file,gdal.GA_ReadOnly)
  
  raster_array = raster.ReadAsArray()
  
  print raster_array
  </code></pre>
  
  <p>Output:</p>
  
  <p><code>&gt;&gt;&gt;array([[ nan,  nan,  nan, ...,  nan,  nan,  nan],
         [ nan,  nan,  nan, ...,  nan,  nan,  nan],
         [ nan,  nan,  nan, ...,  nan,  nan,  nan],
         ..., 
         [ nan,  nan,  nan, ...,  nan,  nan,  nan],
         [ nan,  nan,  nan, ...,  nan,  nan,  nan],
         [ nan,  nan,  nan, ...,  nan,  nan,  nan]], dtype=float32)</code></p>
  
  <p>All values within the array are NaN although I know that there are floating point 32 bit values within the image (Checked with ENVI software)</p>
  
  <p>What am I doing wrong here? Or is there a problem with the suffix?</p>
  
  <p>I have also tried translating the ENVI format to Geotiff using gdal_translate but also the GeoTiff produces the same array.</p>