[RAT support for rasterio (WIP)] Add raster attribute support to rasterio. The property raster_attributes is added to the DatasetReader object and the RAT is returned as an array of dictionaries, where each dictionary has a row's worth of field names/field values. One array is returned for each band in the dataset #rasterio #rat

_base.pxd

# Add in _raster_attributes object
cdef class DatasetReader:
    cdef public object _crs_wkt
    cdef public object _transform
    cdef public object _block_shapes
    cdef public object _raster_attributes

_base.pyx

    @property
    def raster_attributes(self):
        """Returns the default raster attribute table for each band.
        """
        cdef void *hband = NULL
        cdef void *hRat = NULL
        cdef int i, j, col_count
        cdef const char *s_val

        if self._raster_attributes is None:
            if self._hds == NULL:
                raise ValueError("can't read closed raster file")
            self._raster_attributes = []
            for i in range(self._count):
                hband = _gdal.GDALGetRasterBand(self._hds, i+1)
                if hband == NULL:
                    raise ValueError("Null band")
                hRat = _gdal.GDALGetDefaultRAT(hband)
                if hRat == NULL:
                    raise ValueError("Null raster attribute table")

                col_count = _gdal.GDALRATGetColumnCount(hRat)
                data_types = []
                col_names = []
                for j in range(col_count):
                    data_types.append(_gdal.GDALRATGetTypeOfCol(hRat, j))
                    s_val = _gdal.GDALRATGetNameOfCol(hRat, j)
                    col_names.append(s_val.encode('utf-8'))

                band_rat = []
                for i in range(_gdal.GDALRATGetRowCount(hRat)):
                    row = {}
                    for j in range(col_count):
                        dt, cn = data_types[j], col_names[j]
                        if dt == _gdal.GFT_Integer:
                            row[cn] = _gdal.GDALRATGetValueAsInt(hRat, i, j)
                        elif dt == _gdal.GFT_Real:
                            row[cn] = _gdal.GDALRATGetValueAsDouble(hRat, i, j)
                        elif dt == _gdal.GFT_String:
                            s_val = _gdal.GDALRATGetValueAsString(hRat, i, j)
                            row[cn] = s_val.encode('utf-8')
                    band_rat.append(row)
                self._raster_attributes.append(band_rat)
        return self._raster_attributes

_gdal.pxd

# Add in GDAL RAT functions
ctypedef enum GDALRATFieldType:
    GFT_Integer
    GFT_Real
    GFT_String

void *GDALGetDefaultRAT(void *band)
int GDALRATGetColumnCount(void *hRat)
int GDALRATGetRowCount(void *hRat)
const char *GDALRATGetNameOfCol(void *hRat, int col)
GDALRATFieldType GDALRATGetTypeOfCol(void *hRat, int col)
int GDALRATGetValueAsInt(void *hRat, int row, int col)
double GDALRATGetValueAsDouble(void *hRat, int row, int col)
const char *GDALRATGetValueAsString(void *hRat, int row, int col)