Re: [Libexif-devel] Problem editing GPS tags

[Lucía D. R. <ld...@gr...>]

Thank for your answer!!

I've tried doing what exif_entry_initialize() does but I get a compiler
error at:
     exifentry->data = exif_entry_alloc (exifentry, exifentry->size);
because that is a private function on exif-entry.c. So I've tried doing
what that function does, that is:
exifentry->data = exif_mem_alloc (exifentry->priv->mem, exifentry->size);
but this also fails, because the compiler doesn't know
exifentry->priv->mem (error: invalid use of incomplete type
‘ExifEntryPrivate {aka struct _ExifEntryPrivate}’).
And I could find where that is to give some reference to the compiler.

That's why I tried the write.exif.c bit:
buf = exif_mem_alloc(mem, exifentry->size);
 assert(buf != NULL);
/* Fill in the entry */
 exifentry->data = (unsigned char *)buf;
But the firs line results in segmentation fault, so that doesn't work
either.

So I really don't know what to do to make it work like it is supposed to,
that why I asked if is true that it works :))

Thanks again,

Lucía




2014-06-04 21:07 GMT+02:00 Dan Fandrich <da...@co...>:

> On Wed, Jun 04, 2014 at 04:33:51PM +0200, Lucía Díaz Rodríguez wrote:
> > I'm trying to add Exif information to a JPEG file. I've tried the exif
> command
> > line tool (v0.6.21) and the libexif API (v0.6.21-1).
> > Everything works fine until I get to the GPS information (Latitude,
> > LatitudeRef, Longitude and LongitudeRef). I'm able to read it if it
> already
> > exits but i'm not able to create or modify it.
> >
> > Using the exif command line tool (in Mint 16 64bits and also in Ubuntu
> 12.04
> > 32-bits), like so:
> >       exif -c --ifd=GPS --tag=0x0001 --set-value="N" foto-exif.mjpg
> > I get this error:
> >       Setting a value for this tag is unsupported!
> > (Same result using --tag=GPSLatitudeRef).
>
> That's a limitation in the command-line program that flows from missing
> tags in
> the library. There's no good reason for the tags to be missing, except that
> it's really a convenience function that most programs don't actually need.
> It would be possible to add command-line options to exif to support
> arbitrary
> tag data; I'm happy to review patches!
>
> > Using the libexif API, when I try: exif_entry_initialize (exifentry,
> tag), the
> > tag is not listed in the switch cases so default it's used and the entry
> gets
> > FORMAT_UNDEFINED and components=0, which doesn't allocate any memory for
> the
> > associated data.
> > Even if I try to initialize the entry myself (like in the write-exif.c
> example)
> > I'm not able to do so for the data field (I get a segmentation fault on
> > exif_mem_alloc(mem, exifentry->size)).
>
> That should work fine, except that write-exif.c relies on
> exif_entry_initialize
> to create the empty tag, so it's not a complete solution. Take a look at
> the code
> in exif_entry_initialize itself to figure out the rest.
>
> > Now, I've found a bug report from 2005 (https://bugs.debian.org/cgi-bin/
> > bugreport.cgi?bug=309127) mentioning the GPS tags editing. In its
> response it's
> > stated that editing this sort of tags it's possible since exif 0.6.15.
> > Has anything changed since then? If not, would you be so kind as to
> explain to
> > me what am I doing wrong? I've already tried all I could think of and got
> > nowhere.
>
> I don't recall what changes were made since then that would affect this,
> but
> libexif got more strict in a number of ways since then. I don't think any
> existing (working) functionality was removed.
>
> >>> Dan
>
>
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