  >>> from liblas import srs
  >>> import liblas
  >>> s = srs.SRS()
  >>> s.proj4
  ''
  >>> s.proj4 = '+proj=utm +zone=15 +ellps=WGS84 +datum=WGS84 +units=m +no_defs'

  >>> def test_srs():
  ...     if not liblas.HAVE_GDAL: 
  ...         return s.proj4 == '+proj=tmerc +lat_0=0.000000000 +lon_0=-93.000000000 +k=0.999600 +x_0=500000.000 +y_0=0.000 +ellps=WGS84 +units=m '
  ...     if liblas.HAVE_GDAL:
  ...         return s.proj4 == '+proj=utm +zone=15 +ellps=WGS84 +datum=WGS84 +units=m +no_defs '
  ...     return False
  
  >>> test_srs()
  True