Using the Image Catalog Extension

Let's say you have a whole county's worth of DOQ or DRG on a CD or on a hard drive.  You want to be able to zoom in to a few sections of land, scroll around the county, and have the proper TIF image, or images, displayed as a base layer wherever you roam.  One way to accomplish this is to add, as themes, all of the images (DOQ, DOQQ, or DRG) you could possibly want, check them all on to display, and then no matter where you zoomed, the right image, or images, would be displayed.  The disadvantage to this method is that you clutter up the themes list and also add to an excessively long display time.  The solution is to use an Image Catalog, which simply stores the X and Y bounding coordinates of all your desired images, and then calculates the proper image, or images, to display based on the X and Y bounding coordinates of your ArcView display screen.

Image catalogues have been used for quite some time in the ArcInfo world and more recently in the ArcView world but it had always been a manual process in ArcView (automated by Arc commands in ArcInfo) to prepare the database.  The old process in ArcView involved creating a new table with five fields, the first field being the full pathname to the image, and the next fields being the image's minimum and maximum extents for both the X and Y axis's.

This training will walk through the steps involved with using the Image Catalog extension to automate the development of the image reference table.  This extension works well on digital orthoimagery and DRG's.

Step 1 - Obtain the Extension from the ESRI ArcScripts Server

Go to the following ESRI site:

http://gis.esri.com/arcscripts/details.cfm?CFGRIDKEY=912102994

Download the zipped file and extract to the appropriate "ext32" directory on your computer.  On my system, this is located at C:\ESRI\AV_GIS30\ARCVIEW\EXT32.

Step 2 - Load the Extension

Under File/Extensions, click on the "crop2" extension, then click OK.  Click on Make Default if you always want this extension loaded.

Step 3 - Verify the extension has been loaded

There should now be a new icon on the toolbar for Views.  For those of you with graphics awareness deficit disorder, it's a picture of a cat (get it? - catalog - cat!?).

Step 4 - Create an Image Catalog

Select the Image Catalog icon (left click).

Remember that the images must be in a supported image format (tif, jpg, bmp, rs, ras, sun, bsq, bil, bip, lan, gis, img, rlc, sid).

Select the files that you want to add to an image catalog.  In this example, we will add the first five 250K DRG's in this list.

Select OK.  After a few seconds, the database will be made and the following messages will be displayed.  (Actually, the message is a little off.  It adds the image catalog to the View, not to a theme.)

Select Yes.

Step 5 - View images stored in the new Image Catalog

Click on the ImgCat1 theme.  If you are zoomed out to the extent of the ImgCat1 theme, all of the 5 selected DRG will be displayed.  Try zooming in to a smaller area.  As you pan around in the View, the appropriate DRG, or combination of DRG's, will be displayed.  The same process will work for DOQ or other georeferenced imagery.

Step 6 - View images stored in an existing Image Catalog

If there is an existing Image Catalog you wish to view, add it by selecting to add a new theme, switching the Data Source Type to Image Data Source, and then select the appropriate imgcat file.  In other words, you add the image catalog, and not the individual images.

Step 7 - Creating an Image Catalog for a CD

The Image Catalog .dbf file is stored in the directory where the images reside.  This is usually pretty convenient until you want to make an Image Catalog based on data contained on a CD that you do not have write permissions for.  Below is an image of the database format for the Image Catalog.

To create an Image Catalog for CD data, I offer the following steps which have worked for me:

1. Copy the data from the CD to the hard disk of the computer in a temporary directory
2. Use the Image Catalog Extension to create an Image Catalog in that temporary directory
3. Delete the images from the temporary directory but leave the Image Catalog .dbf file
4. Edit the .dbf file in Excel and change the first column IMAGE data to reflect the pathname to the CD
             For instance, c:\data\drg\250k\ashton.tif would become e:\ashton.tif (E is my CD drive)
5. Save the .dbf in a standard data directory (like a C:\DATA directory) and name it something unique
             In this case I would name it 250kimgcatCD.dbf so that I know its a Image Catalog file for the CD containing 250K DRG's
6. Now, any time I want to view 250K DRG, I can just add that 250kimgcatCD.dbf to my view
7. If I click on 250kimgcatCD.dbf and I get an error message, then I know I forgot to put the CD in!
    
   ENJOY!

< Back to ArcView Training