Journal of Surveying Engineering

An attempt to investigate the potential capabilities and accuracy of the PC-based stereovision system in quantification of pavement rut depth was performed. This process was demonstrated using three rutted sections of flexible pavement. Selected highway pavement sections were chosen, using representative criteria that assured randomness in the studied parameters, for semiautomatic rut depth quantification. Surface measurements were represented by two-dimensional and three-dimensional plots, as well as contour maps for the rutted areas. Results obtained by this technique were compared with those obtained by the manual conventional method using a straightedge to check accuracy. Comparison with the manual (conventional) method showed that stereovision using dual charged-coupled device cameras mounted on a stand on a moving vehicle has a consistent potential accuracy of about one pixel (i.e., about 1.5 cm) on average in measuring the rut depth for the three sections. This result was compatible with the human operator's ability to point to the conjugate image points, which has a potential accuracy of about one to two pixels. Advantages of using the stereovision technique to quantify rut depth include remoteness, safety, and real-time potential due to the use of digital images.

This paper discusses different techniques (analytical, manual, and automatic digital) of extracting digital terrain models (DTMs) and their error evaluation. DTMs are mainly used for orthorectification of images, topographic mapping, and engineering design and modeling. Prior to using DTMs for various applications, it is prudent to analyze errors of the extracted DTMs to ensure that they meet the required accuracy standards. DTM data, for about 500 points for a 20 × 50 m grid, were collected using different modes (static, fast static, stop-and-go kinematic) of global positioning system (GPS) surveys on a study area of approximately 0.7 km × 1.0 km in Lavonia, Georgia. Two stereo models at a scale of 1:3,000 have been used to capture DTM and planimetric data on the same study area using three different digital and one analytical photogrammetric systems. These data are compared and analyzed for their compliances with required accuracy standards for orthorectification as well as engineering/topographic mapping. Comparison of analytical and digital photogrammetric systems is made to evaluate accuracy of different systems. Also, a comparison of analytical versus automatic DTM collection was made in four pilot areas using different grid sizes for automatic DTM collection.

The Southeastern Wisconsin Regional Planning Commission (SEWRPC) has, over the past 30 years, established and promoted use of elevations referenced to the National Geodetic Vertical Datum of 1929 (NGVD29). Through international agreement, cooperation, and participation the vertical datums for the entire North American continent were recomputed, readjusted, and published as the North American Vertical Datum of 1988 (NAVD88). This paper summarizes a report prepared to describe differences between those vertical datums throughout the seven-county region served by SEWRPC. The report also includes a brief discussion of the International Great Lakes Datums (IGLD) and describes how IGLD 1985 is related to NAVD88. Conclusions published in the report are that within the seven-county SEWRPC region: (1) third-order datum differences can be interpolated from an isohypsometric map available from SEWRPC; (2) second-order datum differences can be obtained using VERTCON, an interpolation program available from the National Geodetic Survey, Silver Spring, Md; and (3) datum differences at first-order benchmarks should be determined on the basis of field surveys using first-order equipment and observational techniques.