What is a DOQQ?

Okay, if you have come to this web page, you probably are confused by the terms DOQQ, DRG, GIS, etc. This web page will help you get started with using DOQQ imagery. To use imagery, a viewer compatible with the image format is required to view the image or in some cases the imagery can be viewed using Geographical Information System (GIS) software. In most cases, the general public will use a viewer compatible with the image format.

The acronym DOQQ stands for Digital Orthophoto Quarter Quadrangle. In simpler terms, it is a color photograph of a section of Louisiana made from an airplane; however, the film recorded infrared light instead of the normal light that our eyes use. Each photograph covers an area that is approximately four (4) miles across the top by over four and a half (4.5) miles on the side. The photographs are detailed in that each pixel or block of light on the photograph represents one (1) meter or about three (3) feet square on the ground. The photographs are digital in that they have been scanned to create electronic files that are somewhat like the images you see on the web but not exactly. An image on the web is small - usually 3 Kilobytes (Kb) to 100Kb in size. In contrast, each DOQQ is normally 150 Megabytes (Mb) in size, which is approximately 1,500 times larger than most web images. To make the DOQQs manageable and downloadable, the DOQQs have been compressed into MultiResolution Seamless Image Database (MrSid) image format. These MrSid files allow the DOQQs to be compressed from 150Mb to about 3Mb - about 50 times smaller, making the images available through standard modem Internet connections.

Secondly, these MrSID files are georeferenced, that is, they fit on the earth's surface so that you can measure distances and positions using GIS software. With GIS software, you can read coordinates - latitudes and longitudes - from the images. You can measure distances along features such as roads and buildings on the photographs. You can even combine the photographs with other digital maps to print scaled maps.

Therefore, to view these DOQQ images, several steps are provided below on what Internet downloaded software will be required.

In order to use the DOQQs once you have downloaded files from this site, you will need two pieces of software. Download these software applications before you download any DOQQs.

Downloading Winzip

First, you will need the Winzip software from Nico Mak, Inc. to unzip or unpackage the files. A trial copy of Winzip can be downloaded from the Winzip site. Ordering information is available for fully registered copies of Winzip. To visit the Winzip site and download the trial copy of Winzip, click on the Winzip logo to right.

Downloading the MrSid Viewer (Needed for DOQQ 1998 images)

Second, if you do not have a GIS such as Intergraph Geomedia or ESRI ArcView that can display the MrSid files, you will need a viewer. LizardTech, the maker of MrSid, also has a free stand alone viewer that you can download and install.

• To download the Lizardtech viewer for Windows, click here.
  
• To visit the Lizardtech web site for other MrSid tools including viewers for nonWindows operating systems, click here.