id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
30489	Django RasterField deserialization bug with pixeltype flags	Ivor Bosloper	nobody	"After inserting some raster data with raster2pgsql into a Django model table with a RasterField column, I get a `list index out of range` when querying the table with a Django Queryset. 

{{{
...
File ""django/contrib/gis/db/models/fields.py"" in from_db_value
  360.         return connection.ops.parse_raster(value)
File ""django/contrib/gis/db/backends/postgis/operations.py"" in parse_raster
  369.         return from_pgraster(value)
File ""django/contrib/gis/db/backends/postgis/pgraster.py"" in from_pgraster
  57.         pixeltype = POSTGIS_TO_GDAL[pixeltype]
}}}

It turns out the `pixeltype` value used is 39 while the `POSTGIS_TO_GDAL` list is only 16 elements long. The database field contains valid data but can not be deserialized with Django. 

**Steps for reproduction:**

{{{
# Django model
class RasterModel(models.Model):
    rast = models.RasterField(srid=4326)

# raw sql, single pixel raster with nodata bit set
insert into app_rastermodel values(1, REPLACE('01 0000 0100 0000000000000000 0000000000000000 0000000000000000 0000000000000000 0000000000000000 0000000000000000 E6100000 0100 0100 6 2 03 03', ' ', '')::raster);

# query generating Exception
RasterModel.objects.get(pk=1)
}}}


**Analysis**: if we look at the [https://trac.osgeo.org/postgis/wiki/WKTRaster/RFC/RFC1_V0SerialFormat Raster specification], the pixeltype is a byte of which the 4 highest bits are flags and the lowest 4 bits are the real pixeltype, but the Django deserialization code only considers one bit-flag:

{{{
# django/contrib/gis/db/backends/postgis/pgraster.py
def from_pgraster(data):
        ...
        # Subtract nodata byte from band nodata value if it exists
        has_nodata = pixeltype >= 64
        if has_nodata:
            pixeltype -= 64
       ...
}}}

I have created (my first django) patch and hope somebody can assist me in getting it correct and merged."	Bug	new	GIS	2.2	Normal		RasterField		Unreviewed	1	0	0	0	0	0