About the research
This research involved two studies: one to determine the local geoid to obtain mean sea level elevations from a global positioning system (GPS) to an accuracy of ±2 cm, and the other to determine the location of roadside features such as mile posts and stop signs for safety studies, geographic information systems (GIS), and maintenance applications, from video imageries collected by a van traveling at traffic speed. Four phases of local geoid determinations were conducted for nine stations in Story County. The variation fluctuated with time and the mean of all three had standard errors of less than ±2 cm. It was noted that the variations in local geoid may be due to motion of the axis of rotation of the earth. A need for a fixed-height antenna for all stations was indicated. It was also found that two sessions of observation can be used to detect blunders. It is recommended that the variation of local geoid over a long period of time, about 4?18 years, be studied so as to determine the validity of the moving average. A video logging van capture imageries at three test sites: Grand Avenue, an urban site; EDM baseline, a rural site; and US30 in Nevada, a freeway, at 55 mph. Evaluation of the data showed that the roadside feature location can be determined with relative accuracy better than 10 cm and absolute accuracy of ±2 m, depending on the global positioning system. The method developed was used to determine the state plane coordinates of mileposts and anchor points located along a 14-mile portion of US 30 from Ames to Nevada, Iowa. This information can be used in GIS and maintenance applications, as well as in safety studies. It is recommended that the Iowa Department of Transportation update the video logging van with a kinematic carrier phase GPS and conduct research with automatic data capture and by creating virtual roads.