Remote Sensing Tools

In Part 1 and Part 2 of this series, we explored the common use and options for a set of utilities to handle Geotiff metadata tags. This allowed us to be able to output and store that data in text format for later retrieval, so that we could then be able to install it into an image edited and exported out of Photoshop®.

What can we do then, when we wish to export a Geotiff .tif file from an actual Remote Sensing or GIS program that supports Geotiff prior to importing and editing in Photoshop? How can we ensure we’ll retain the metadata tags, allowing us to load the images we edit in Photoshop back into a GIS program?

We have two options in this case, provided we have a program that supports the export of Geotiff .tif images, and their associated metadata:

• Export from a GIS program, specifying the tags you would like to output to text files — in addition to the Geotiff file you’re exporting.
• Export a Geotiff file, and then use the listgeo and geotifcp utilities as mentioned in the previous parts of this tutorial.

Let’s look at the first option, as we’ve already covered the second. In this example, I’ll be using Global Mapper, which is an incredibly powerful GIS and mapping program that readily supports a wide range of geospatial formats and functions. It’s also priced in a range that makes it quite accessible for both the professional and the hobbyist.

Prerequisites

Once again, if you require a sample Geotiff image, you may download the example I’ve provided here:
Sample Geotiff (~350 KB download, .zip format)

Exporting from Global Mapper

Exporting a Geotiff from Global Mapper is rather simple. The following will walk a user through loading and exporting a Geotiff file, prior to being imported and edited in Photoshop:

1. To open, go to File → Open Data File(s) or [Ctrl+O], browse to where your image is stored and load it.
   (Or, click the Folder icon in the toolbar.)
2. To export, go to File → Export Raster and Elevation Data → Export GeoTIFF…
3. In the GeoTIFF Options tab, make sure you check the following options:
   (See the reference image for a visual example.)
   • 24-bit RGB (Full Color, Large Storage Required)
   • Generate TFW File
   • Generate PRJ File
4. Click OK, and save your image at the prompt.

That’s it! You should now have an exported Geotiff .tif file with both an ESRI type coordinates file, known as a TIFF World File (TFW), and a standard Projections (PRJ) file. Both of these files are text, so you can also view them in any text editor, such as Notepad.

Now — if you were to edit and save your Geotiff .tif image in a program such as Photoshop, you simply ensure that the text files have the same filename as the image saved — and Global Mapper and most other GIS programs will automatically associate those metadata text files with the image.

The second option, which was briefly mentioned, is to export Geotiff files out of your GIS program and utilize the listgeo and geotifcp utilities before and after editing in Photoshop. Either option will work, and it only depends on which method you wish to use.

Caveats

The same principle applies in this case, as in the previous tutorials. Resizing or cropping geospatial images in Photoshop isn’t recommended. This can lead to a number of problems associated. However, if you have a GIS editor such as Global Mapper, you can make these changes to your imagery either before or after editing in Photoshop without any concerns.

Advantages

One advantage to working with a GIS program and Photoshop within a work-flow, greatly depends on whether or not your program supports exporting imagery with any amount of overlap. Global Mapper, for example, allows a user to export an entire map into tiles with optional overlap — allowing for more flexibility in editing between those tiles in Photoshop.

Having the ability to export Geotiff files with overlap enables a user to edit extremely large datasets and maps in Photoshop — and then import those edited image tiles back into a GIS viewer or editing program. One of the reasons this is so powerful as an option is because the majority, if any, of the GIS programs available today lack the flexibility and the tools of a powerful image editor such as Photoshop.

One other great advantage that GIS programs offer, is the ability to load various other geospatial formats — which you can then export as Geotiff .tif files to be edited in Photoshop.

More to come…

In the next and final tutorial, Geotiff & Photoshop, Part 4, we’ll introduce the use of a plugin that’s specifically designed to add GIS capabilities to the Photoshop environment. This plugin is also available for Mac users, and allows for a standard interface familiarity that Photoshop users may be more comfortable with.

For more information on the GIS editing program mentioned in this part of the series, you can visit the developer’s page at the following Web site address:
http://www.globalmapper.com/

For More Information

For information on other GIS programs that offer similar functions and support for Geotiff, simply conduct a search with your favorite search engine. There are a number of Open Source and commercial software products available, and for nearly every OS environment. Or, you can visit the following Web site prepared by Ned Horning and staff at the American Museum of Natural History’s Center for Biodiversity and Conservation Biodiversity Informatics Facility, which lists a well rounded set of powerful GIS capable programs:
Open Source GIS and Remote Sensing Software

The CBC has also prepared a great introductory tutorial on how to load Landsat TM and ETM+ .tif images into Photoshop here:
Viewing Landsat TM images with Adobe Photoshop