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Track: Database Design and Automation
Gary Smith
Green Mountain GeoGraphics, Ltd.
PO Box 2171
S. Burlington, VT 05407
Telephone: 802-878-6746
Fax: 802-878-0161
E-mail: gsmith@zoo.uvm.edu
Harry Roush
Review Criteria and Methodology for Digital Orthophotos Using ArcView
Defining Issue: The use of digital orthophotography as the base for both new and existing geographically referenced information continues to expand. While the addition of imagery can significantly enhance a GIS database, care must be given to ensure that the quality of the imagery meets a defined standard. Arriving at a definable standard that is both repeatable and acceptable to all concerned is very important. It is also required if the quality of the associated database that will be built from this orthophotography is to remain high. GIS Solution: In the review of ortho imagery, ArcView GIS becomes much more than a viewing tool. With the addition of the Spatial Data Analyst, display and incorporation of the associated data elevation model (DEM) is possible. From each image, an inexpensive print can be generated that can accurately pinpoint any defects, errors, or anomalies. Methodology: At the heart of a GIS is a database built on representation of reality. As such, features are presented as a
point, line, polygon, or grid. Adding an image to the background of a display serves to add credibility to a database by developing a closer tie to reality. This confidence level leads to a quick acceptance and use of the image to capture additional information for use within the database. While the image may appear correct, experience has shown that a careful review of imagery is necessary. It is important that issues of map accuracy standards be understood in conjunction with pixel size. Understanding DEM collection procedures is very important in the design of spatial accuracy tests that can be applied across the area being imaged. The intent of this paper is to share the experience of the State of Vermont as the State's orthophoto program has shifted from analog products to today's digital imagery over the past three years. This review process continues to evolve, and with the addition of ArcView Version 3 software's capabilities and the use of the Spatial Data Analyst, a consistent methodology has
been established. This comes from the experience of reviewing more than 500 images covering more than a million acres of the State. Software: This application makes extensive use of ArcView, the Spatial Data Analyst, and ArcInfo to build the new framework and assess image quality and accuracy.
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