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