EXIF 2.31 Enhancement for LibTiff and some other bugfixes

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EXIF 2.31 Enhancement for LibTiff and some other bugfixes

Dear all

LibTiff version 4.0.7 is enhanced with EXIF- and GPS- tags according to EXIF 2.31 specification. (http://www.cipa.jp/std/documents/e/DC-008-Translation-2016-E.pdf)

The patches and files are provided in the BugList as enhancement:    (http://bugzilla.maptools.org/show_bug.cgi?id=2703)
Furthermore, additional enhancements and corrections are included:1) Data type of GPS_IFD and EXIF_IFD tags are corrected from TIFF_IFD8 to TIFF_LONG as of    EXIF 2.31 specification.     See also http://bugzilla.maptools.org/show_bug.cgi?id=25392) Writing and reading of rational values in custom fields is enhanced resulting in nearly    double precision - standard LibTiff only has float precision. This feature can be enabled    with #define RATIONAL2DOUBLE in tiffiop.h.   However, if RATIONAL2DOUBLE is defined, parameter type for reading and writing TIFF_RATIONAL    parameters using TIFFSetField() and TIFFGetField() have to be adapted to 'double' as defined    in tif_dirinfo.c. The function IsRational2Double() indicates, if the library was compiled with this option.See also Rationals with true DOUBLE precision for CUSTOM defined tags (http://bugzilla.maptools.org/show_bug.cgi?id=2542)Attention:3) The "#define IGNORE 0" in tif_dirread.c collides with the GPS tag "VersionID=0"
   and prevents the tag to be read. Therefore, the #define should be redefined
   for example to "#define IGNORE 65534 //(-2)"4) FILESOURCE and SCENETYPE are defined as TIFF_UNDEFINED.
   However, TiffLib does not read TIFF_UNDEFINED with field_readcount==1!
   Therefore, they should be defined as TIFF_BYTE.Complete changed files regarding to LibTiff version 4.0.7 are attached:   tiffiop.h; tif_dirwrite.c; tif_dirinfo.c; tif_dirread.c; tif_dir.c; tiff.h; tiffio.h; tif_dir.hFurthermore a patch file against version 4.0.7 is attached too:    TiffLib-4.0.7_EXIF-231_.patchTwo example files for writing/reading EXIF and GPS tags are provided within the "test" directory.  Because EXIF sub-directory functionality in LibTiff misuses the mechanism of multipage TIFF writing,damaged or incomplete directory-trunks are generated easily without intention.- custom_dir_EXIF_231.c- custom_dir_MultiPage_EXIF.cThey give some hints, how to read / write tags with the different types.This information is provided in the BugList as enhancement:    (http://bugzilla.maptools.org/show_bug.cgi?id=2703)For application of custom directories refer to:"Custom and EXIF directory read/write", by Frank Warmerdam http://www.asmail.be/msg0055058657.html and"Creating private IFD", by  http://www.asmail.be/msg0055095680.htmlRegardsSu

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