Thanks, Niles, for you respond.
Now it is clear that TIFFGetField() still returns a number
of null
terminated strings, not a flag (true/false). Wish to see
your explanation
somewhere in libgeotiff manual or at least in GeoTIFF FAQ.
Low level commands are used to handle georeference in LIDAR
data (LAS 1.1) exchanging geoTIFF info in binary form. Dont
need to parse
tags, just throwing from geoTIFF and back as is.
Happy programming!
gok
-----Original Message-----
From: Niles Ritter [mailto:ritter earthlink.net]
Sent: Saturday, February 03, 2007 1:39 PM
To: Gennady Khokhorin
Cc: Phil Harvey; tifflists.maptools.org; geotifflists.maptools.org
Subject: Re: [Geotiff] RE: [Tiff] Re: get
tifftag_geoasciiparams string
In the TIFF spec it indicates that an ASCII tag can,
theoretically,
contain multiple values, each separated by a NULL
terminator. This
has proven to be a problem in practice, and so no one really
uses
multi-valued ASCII tags as described in the TIFF spec.
The TIFFGetField should return the number of
null-terminated
strings, and not the length. For most TIFF tags on the
planet,
you should therefore get either 1 or 0.
To avoid null-termination miseries, the GeoTIFF spec stores
its strings in a single ASCII tag, with '|' pipe-delimiters
(tacitly assuming that the data itself contains no pipes).
So,
calling TIFFGetField directly on a GeoTIFF image should
give
you back a value of 1, and store the string in &data. It
is
up to you to parse out the separate pipe-delimited values.
Not sure why you want to use the lower-level libtiff to
roll-your-own GeoTIFF, but best of luck, in any case. The
first thing you will find is that you will, at least, need
to use the "xtiff" tiff-extender code in the
libgeotiff
source so that the libtiff image-tag parsing code will
recognize the "unknown" GeoTIFF tags.
--Niles.
On Fri, 2007-02-02 at 10:36 -0900, Gennady Khokhorin wrote:
> Thanks, Phil, for respond.
> I agree: docs are pure. I have the same manual.txt for
libgeotiff.
>
> Still can not find any reference for return from
TIFFGetField(tif, TIFFTAG_GEOASCIIPARAMS, &data)
> command. The other two return number of elements as a
parameter:
> TIFFGetField(tif, TIFFTAG_GEOKEYDIRECTORY, &size,
&data);
> TIFFGetField(tif, TIFFTAG_GEODOUBLEPARAMS, &size,
&data);
>
> TIFFGetField() description in
tiff-3.8.2htmlmanTIFFGetField.3tiff.html shows
> in "Autoregistered tags" sample that ascii
tag should be handled the same way. But
> real code is different.
>
> I want to use TIFF approach to handle tags (shorts,
doubles, ascii) as an arrays
> rather then GTIFFKeySet/GTIFFKeyGet for each tag.
Thanks to gdal it handles geoTiff
> great.
>
> Any help, please!
>
> Gennady
>
> -----Original Message-----
> From: tiff-bounceslists.maptools.org
> [mailto:tiff-bounceslists.maptools.org]On
Behalf Of Phil Harvey
> Sent: Thursday, February 01, 2007 3:08 PM
> To: tifflists.maptools.org
> Subject: [Tiff] Re: get tifftag_geoasciiparams string
>
>
> Sorry, I meant to give you this reference so you can
download the
> GeoTiff library, which I believe includes
documentation:
>
>
ftp://ftp.remotesensing.org/geotiff/libgeotiff/libgeotiff-1.
2.3.tar.gz
>
> - Phil
>
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