[Geotiff] Re: Geotiff

Sun Mar 5 03:37:56 EST 2006

Robert and Thomas,

I was out travelling this week, but I finally had an opportunity to sit down
and check and answer messages - which I noticed the similarities in both of
yours. Georeferenced raster imagery [primarily Geotiff] in Photoshop is
actually my primary focus in what I do, so hopefully I can help elaborate or
point-out more options that you might find more comfortable.

I saw that Frank mentioned in another message that the FAQ has been updated
to include for what one can do as the work-around to strip the Geotiff
metadata from the Geotiff files, and then to 'restuff' those tags into any
.tif image that's been edited in a raster program that does not support the
Geotiff format. To elaborate on, or to possibly include options you might be
more comfortable with, I'll outline this as best I can in the following, so
that you can explore what might be best for your needs.:

1) The listgeo and geotifcp utilities, which are command-line programs run
from the shell (DOS shell on Windows OS platforms). Those utilities are
linked from the main Geotiff utilities page here:
http://www.remotesensing.org/geotiff/geotiff.html The commands needed for
both utilities are located on the FAQ page for Geotiff as well if you need
it as a reference.

1a) There is a GUI that was contributed by Geosage that allows a user to do
the same thing as Frank outlined in the FAQ, if it's more comfortable or
productive working in a visual point-and-click environment you're more
familiar with. (I tend to lean or prefer this way as well). Unfortunately,
you won't be able to batch as it handles one file at a time.

1b) If you're familiar with DOS scripting, you can find ways of automating
listgeo and geotifcp by creating DOS .bat (batch) files to increase
simplicity or consistency of use, or to allow for batching directories
easily. This can be executed in several ways, and if you're familiar with
the several options in Windows setting up .bat scripts and your Windows
environment you might wish to explore this as well.

1c) You can extent most platforms with languages such as PERL or VBScript,
to create automations to handle several optional tasks and automations.

2) Avenza has released the only *available* plugin to Photoshop that allows
users to work with many geographic imagery formats [including Geotiff],
preserving the metadata or allowing for other options of export, etc. PS CS2
is required - other Photoshop plugin compatible programs or older versions
are not supported at this time (ie: PaintShop Pro, GIMP, etc). This tool may
be more to your liking, as it allows for the ability to crop the imagery and
to create mosaics, recalculating the coordinates among other things - as an
actual geographic imagery production tool. Unfortunately, GI cannot be
automated using Actions or Scripts, but that is more of an Adobe SDK issue
as opposed to what Avenza is capable of including. It's still an incredibly
useful tool for what it sounds like you're looking to accomplish, if you're
simply editing limited amounts of geographic raster imagery and would simply
like the added benefit of being able to easily work with the Geotiff format
and the tools that add value in those programs. It can handle larger amounts
of data if you have a machine that can handle larger file sizes as well. You
can find the plugin at Avenza's web site here.: http://www.avenza.com/

Notes:

Note also, that if you import the image in any way to one of these programs,
resizing or resampling/rescaling is generally not a good thing to do. If
you're exporting an image for print, a Geotiff is not necessary of course -
but if you wish for your imagery to view properly in a GIS application or
program, this could lead to several known issues. Retaining the resolution
is suggested when working in and out of any raster program such as Photoshop
(including the use of the Geographic Imager plugin).

I also can't stress enough to familiarize yourself with the Geotiff metadata
keys and what they represent. It's critical in nearly all instances that the
metadata reflects accurately what the image being presented or stored
actually is. In the case of resampling/rescaling, if the resolution is
different from what's actually in the file - and regardless if the
percentage of the scale is half or 200% of the original image, the metadata
will probably have to be edited manually to reflect this. That also can't
guarantee whether the pixels have scaled accurately or correctly, which
might lead to discrepencies or display issues among other potential problems
that can be created. I generally don't recommend that this take place in one
of these programs but rather that is the time to allow a geographic program
to take care of those edits for you.

I hope this has been of some help to you both, and potentially others
reading. It may seem like a number of things to familiarize with and absorb,
but once you've gotten started with the basics and understanding the caveats
and work-arounds associated [currently (I hope they're not forever in the
distant future)], you'll be able to explore several other options with
Geotiff and 'mainstream' raster programs that might add value to your needs
or workflow.

Take care, and good luck,
Daniel Denk

On 2/28/06, Frank Warmerdam <warmerdam at pobox.com> wrote:
>
> Robert Lines wrote:
> > I have been working with geotiffs for a little while.  I am trying to
> > draw borders on land and label them in Geotiff format.  Is there a way
> > to draw on geotiffs or take off the georeferened tags edit the tiff and
> > place the tags back on.  Thank you in advance
>
> Robert,
>
> I don't have any suggestions for the first (editing a geotiff without
> disturbing the tags).  But you can save the tags to a text file, edit
> the image, and then reapply them using the libgeotiff listgeo and
> geotifcp utilities.
>
> I have written an FAQ entry about this since it is a common question.
>
>   http://geotiff.maptools.org/faq.html#preserve_metadata
>
> Best regards,
> --
>
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam,
> warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | Geospatial Programmer for Rent
>
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>
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