Changes between Version 1 and Version 4 of Ticket #30489


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Timestamp:
May 19, 2019, 2:42:47 PM (6 years ago)
Author:
Ivor Bosloper
Comment:

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  • Ticket #30489

    • Property Triage Stage Unreviewed → Accepted

  • Ticket #30489 – Description

    v1 v4  
    2828
    2929
    30 **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:
     30**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. Quoting the specification:
     31
     32{{{
     33 Pixel type and storage flag
     34 ---------------------------
     35
     36 Pixel type specifies type of pixel values in a band.
     37 Storage flag specifies whether the band data is stored
     38 as part of the datum or is to be found on the server's
     39 filesytem.
     40
     41 There are currently 11 supported pixel value types, so 4
     42 bits are enough to account for all. We'll reserve
     43 the upper 4 bits for generic flags and define upmost as
     44 storage flag:
     45 
     46 #define BANDTYPE_FLAGS_MASK 0xF0
     47 #define BANDTYPE_PIXTYPE_MASK 0x0F
     48
     49 #define BANDTYPE_FLAG_OFFDB     (1<<7)
     50 #define BANDTYPE_FLAG_HASNODATA (1<<6)
     51 #define BANDTYPE_FLAG_ISNODATA  (1<<5)
     52 #define BANDTYPE_FLAG_RESERVED3 (1<<4)
     53}}}
     54
     55However, Django deserialization code only considers a single flag (`BANDTYPE_FLAG_HASNODATA`, bit 6, value 64):
    3156
    3257{{{
    … …  
    4166}}}
    4267
    43 The erroneous pixeltype 39 in my example actually had the `BANDTYPE_FLAG_ISNODATA` (32) bit set which indicates all rastervalues are nodata.
     68The erroneous pixeltype 39 in my example actually had the `BANDTYPE_FLAG_ISNODATA` (bit 5, value 32) bit set which indicates all rastervalues are nodata.
    4469
    4570I have created (my first django) patch and hope somebody can assist me in getting it correct and merged.
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