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2005.03.03 19:27 "Re: LibTIFF question", by Frank Warmerdam
On Thu, 3 Mar 2005 13:19:50 -0600 (CST), Bob Friesenhahn wrote: > Is there any way to quench the "unknown tag" errors if the application > plans to handle them? It would be nice if there was a way for the > application to tell libtiff in advance that it is going to handle > certain tags. Bob, Certainly. Predefine the tags with TIFFMergeFieldInfo. The tricky part is that each TIFF file instance carries a list of tag definitions and you need to pre-define them as part of the open process before tags start to get processed. This works by installing a tag extender that will be invoked for each TIFF file opened. The GeoTIFF library does this with the bulk of the code of interest being found in libgeotiff/xtiff.c which I am appending for people to review. I wrote up some of this in the Libtiff docs at: http://www.remotesensing.org/libtiff/addingtags.html This is a subtopic of the "Modifying the TIFF Library" page on the web site. I would agree that the TIFFGetField() man page needs to be updated to reflect how it behaves for tags that have not been predefined. Best regards, -- ---------------------------------------+-------------------------------------- I set the clouds in motion - turn up | Frank Warmerdam, warmerdam@pobox.com light and sound - activate the windows | http://pobox.com/~warmerdam and watch the world go round - Rush | Geospatial Programmer for Rent Attachment xtiff.c /* * xtiff.c * * Extended TIFF Directory GEO Tag Support. * * You may use this file as a template to add your own * extended tags to the library. Only the parts of the code * marked with "XXX" require modification. * * Author: Niles D. Ritter * * Revisions: * 18 Sep 1995 -- Deprecated Integraph Matrix tag with new one. * Backward compatible support provided. --NDR. */ #include "xtiffio.h" #include <stdio.h> #include "cpl_serv.h" /* Tiff info structure. * * Entry format: * { TAGNUMBER, ReadCount, WriteCount, DataType, FIELDNUM, * OkToChange, PassDirCountOnSet, AsciiName } * * For ReadCount, WriteCount, -1 = unknown. */ static const TIFFFieldInfo xtiffFieldInfo[] = { /* XXX Insert Your tags here */ { TIFFTAG_GEOPIXELSCALE, -1,-1, TIFF_DOUBLE, FIELD_CUSTOM, TRUE, TRUE, "GeoPixelScale" }, { TIFFTAG_INTERGRAPH_MATRIX,-1,-1, TIFF_DOUBLE, FIELD_CUSTOM, TRUE, TRUE, "Intergraph TransformationMatrix" }, { TIFFTAG_GEOTRANSMATRIX, -1,-1, TIFF_DOUBLE, FIELD_CUSTOM, TRUE, TRUE, "GeoTransformationMatrix" }, { TIFFTAG_GEOTIEPOINTS, -1,-1, TIFF_DOUBLE, FIELD_CUSTOM, TRUE, TRUE, "GeoTiePoints" }, { TIFFTAG_GEOKEYDIRECTORY,-1,-1, TIFF_SHORT, FIELD_CUSTOM, TRUE, TRUE, "GeoKeyDirectory" }, { TIFFTAG_GEODOUBLEPARAMS, -1,-1, TIFF_DOUBLE, FIELD_CUSTOM, TRUE, TRUE, "GeoDoubleParams" }, { TIFFTAG_GEOASCIIPARAMS, -1,-1, TIFF_ASCII, FIELD_CUSTOM, TRUE, FALSE, "GeoASCIIParams" }, #ifdef JPL_TAG_SUPPORT { TIFFTAG_JPL_CARTO_IFD, 1, 1, TIFF_LONG, FIELD_CUSTOM, TRUE, TRUE, "JPL Carto IFD offset" }, /** Don't use this! **/ #endif }; #define N(a) (sizeof (a) / sizeof (a[0])) static void _XTIFFLocalDefaultDirectory(TIFF *tif) { /* Install the extended Tag field info */ TIFFMergeFieldInfo(tif, xtiffFieldInfo, N(xtiffFieldInfo)); } /********************************************************************** * Nothing below this line should need to be changed. **********************************************************************/ static TIFFExtendProc _ParentExtender; /* * This is the callback procedure, and is * called by the DefaultDirectory method * every time a new TIFF directory is opened. */ static void _XTIFFDefaultDirectory(TIFF *tif) { /* set up our own defaults */ _XTIFFLocalDefaultDirectory(tif); /* Since an XTIFF client module may have overridden * the default directory method, we call it now to * allow it to set up the rest of its own methods. */ if (_ParentExtender) (*_ParentExtender)(tif); } /* * XTIFF Initializer -- sets up the callback * procedure for the TIFF module. */ static void _XTIFFInitialize(void) { static int first_time=1; if (! first_time) return; /* Been there. Done that. */ first_time = 0; /* Grab the inherited method and install */ _ParentExtender = TIFFSetTagExtender(_XTIFFDefaultDirectory); } /** * GeoTIFF compatible TIFF file open function. * * @param name The filename of a TIFF file to open. * @param mode The open mode ("r", "w" or "a"). * * @return a TIFF * for the file, or NULL if the open failed. * This function is used to open GeoTIFF files instead of TIFFOpen() from libtiff. Internally it calls TIFFOpen(), but sets up some extra hooks so that GeoTIFF tags can be extracted from the file. If XTIFFOpen() isn't used, GTIFNew() won't work properly. Files opened with XTIFFOpen() should be closed with XTIFFClose(). The name of the file to be opened should be passed as <b>name</b>, and an opening mode ("r", "w" or "a") acceptable to TIFFOpen() should be passed as the <b>mode</b>.<p> If XTIFFOpen() fails it will return NULL. Otherwise, normal TIFFOpen() error reporting steps will have already taken place.<p> */ TIFF* XTIFFOpen(const char* name, const char* mode) { TIFF *tif; /* Set up the callback */ _XTIFFInitialize(); /* Open the file; the callback will set everything up */ tif = TIFFOpen(name, mode); if (!tif) return tif; return tif; } TIFF* XTIFFFdOpen(int fd, const char* name, const char* mode) { TIFF *tif; /* Set up the callback */ _XTIFFInitialize(); /* Open the file; the callback will set everything up */ tif = TIFFFdOpen(fd, name, mode); if (!tif) return tif; return tif; } TIFF* XTIFFClientOpen(const char* name, const char* mode, thandle_t thehandle, TIFFReadWriteProc RWProc, TIFFReadWriteProc RWProc2, TIFFSeekProc SProc, TIFFCloseProc CProc, TIFFSizeProc SzProc, TIFFMapFileProc MFProvc, TIFFUnmapFileProc UMFProc ) { TIFF *tif; /* Set up the callback */ _XTIFFInitialize(); /* Open the file; the callback will set everything up */ tif = TIFFClientOpen(name, mode, thehandle, RWProc, RWProc2, SProc, CProc, SzProc, MFProvc, UMFProc); if (!tif) return tif; return tif; } /** * Close a file opened with XTIFFOpen(). * * @param tif The file handle returned by XTIFFOpen(). * * If a GTIF structure was created with GTIFNew() * for this file, it should be freed with GTIFFree() * <i>before</i> calling XTIFFClose(). */ void XTIFFClose(TIFF *tif) { TIFFClose(tif); }