Integrating Control Points into NAIP in Support of Absolute Horizontal Accuracy

U.S. Department of Agriculture, Farm Services Agency Aerial Photography Field Office

The National Agriculture Imagery Program (NAIP) acquires aerial imagery during the agricultural growing seasons in the continental United States. A primary goal of the NAIP program is to make digital orthophotography available to governmental agencies and the public within a year of acquisition.

Absolute accuracy is determined by using a set of control points. These control points need to be identifiable on 1 meter NAIP imagery so a corre-sponding point can be placed on the image where the control point should be located. The distance between the control point and the corresponding point can then be measured and used to determine absolute accuracy. The absolute accuracy specification for NAIP requires 95 percent of well-defined points to be within 6 meters of true ground.

Every year a control point is used in the NAIP inspection it is given a quality rating on a scale of 1 to 5, with 1 an excellent point, easily identifiable with quality support information, and 5 a very poor point, very hard to identify with no support information.

Now that the database has good national coverage, this information will be very useful when trying to obtain more control points either by purchasing or partnering with other agencies. It provides the U.S. Department of Agriculture with focus areas that have points but are hard to work with or lack quality compared to points in other areas.

Courtesy of U.S. Department of Agriculture, Farm Services Agency Aerial Photography Field Office, 2010.

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