SaLIS Vol. 61, no. 3

September 2001

 

Mobile Mapping Technology: Ten Years Later (Part Two)

 

Dorota A. Grejner-Brzezinska

 

During the last decade of the twentieth century the concept of Mobile Mapping Systems (MMS) has been established and evolved from rather simple land-based systems to more sophisticated, real-time multi-tasking and multi-sensor systems, operational in land and airborne environments. Mobile Mapping technology has made a remarkable progress, notably expanding its use in remote sensing, surveying and mapping. New systems are being developed and built for specialized applications. Part One of this paper (published in Surveying and Land Information Systems 61(2), pp. 75-91) focused on the evolution of the MMS concept, with special emphasis on the advancements in imaging and navigation components and on the benefits that the technology brought to the mapping and GIS community. In addition, fundamentals of GPS/INS integration as a tool for direct platform orientation (DPO) were presented. In Part Two, the notion of direct georeferencing is explained and compared to the traditional image geo-registration technique. Moreover, the significance of multi-sensor system calibration and its impact on the positioning accuracy are presented. The paper concludes with examples of currently attainable navigation performance and future perspectives of MMS technology.

 

 

Airborne GPS Photogrammetry in  Low-Altitude Applications Part Two

 

Peter Kuntu-Mensah and Raymond J. Hintz

 

The use of GPS to determine camera exposure positions has been shown to drastically reduce and possibly eliminate the number of ground control points required in a photogrammetric aerial triangulation. This notwithstanding, the application of airborne GPS in low-altitude photogrammetry has been virtually non-existent. The research described in this paper suggests that airborne GPS can provide measurement accuracies suitable for engineering design and similar applications.

 

Transformation of Datasets  in a Linear-based Map Conflation Framework

 

Yerahmiel Doytsher, Sagi Filin and Eti Ezra

 

Overlapping datasets originating from different sources tend to have positional discrepancies between similar objects. The underlying process that generates these discrepancies is usually unknown and is non-homogenous in nature. The non-homogeneity suggests that registration of the datasets should be performed using local transformations; the type of local transformations is, however, an open question. Usually, a local rubber-sheeting transformation that utilizes nodes as counterpart features is applied to solve these discrepancies. However, point-based transformation is adequate only for simple cases. This paper presents a local transformation algorithm based on counterpart linear features. The transformation is more general in essence and suitable to a wide range of cases, especially for transformation of spatial geographic data. The line-based transformation is presented here as part of a linear-based map conflation algorithm, a framework under which this transformation is most likely to be encountered in geographic information systems (GIS). Nevertheless it can also be applied separately as part of different applications.

 

 

Using GPS to Detect Vertical Movement  Along a Leveling Line in Imperial Valley, California

 

Wesley Parks

 

A GPS survey designed to precisely estimate ellipsoidal height was conducted in 1997 on benchmarks of a precise leveling line in Imperial Valley, California, a line actively leveled to monitor ground subsidence related to geothermal fluid withdrawal. The survey duplicated a 1995 survey. Data were analyzed to estimate differences in ellipsoidal height between adjacent benchmarks. GPS-derived height differences for 1997 were compared to 1995 differences. Discrepancies were analyzed to identify leveling sections in which vertical movement might have occurred. Three such sections were identified.

 

 

Boundary Retracement Based on Maps, Plats, and Surveys

 

Andrew C. Kellie

 

This paper examines the importance attached by the courts to maps, plats, and surveys used in the description of land. The general rules regarding maps, plats, and surveys in boundary retracement are examined and specific cases that have come before the courts are reviewed in an attempt to understand how the courts have applied the general principles in actual litigation. In general, a call for a map, plat, or survey is considered inferior to the intent, but superior to a call for monuments, although exceptions to this ordering certainly exist. Interpretation of conflicting elements within or on the plat itself relies upon the rules of construction normally used with written instruments. Finally, boundaries shown on a plat as abutting roads, streams, or the sea are treated just as written descriptions of these features. The boundaries of the property owner in such cases depend on the graphical description of these features on the plat or map involved.

 

 

Locally Produced Geodetic Control and Cadastral Framework Data in the United States

 

David Tulloch

 

A recent national survey provides a nationwide description of framework data. The National Framework Survey was conducted by the National States Geographic Information Council and the Federal Geographic Data Committee. This paper presents findings from that survey about locally produced geodetic control and cadastral framework data. Included are specifics about spatial accuracy, completeness, and different data production activities. While the survey results provide evidence of the substantial work being done on these framework themes, they also illustrate the difficulties that remain before achieving the state goal of a national spatial data infrastructure. The results suggest that data about geodetic control, cadastral reference and publicly owned land framework are being produced widely, but with some differences of quality and content. Ultimately these findings raise a question as to future strategies for the development of an NSDI. In particular, the survey highlights the inevitable conflict of using locally produced data as a fundamental element within a much larger network of data.

 

 

Surveying Notes

 

Superstar Surveying: Hollywood Heroes and Movietone Measurements!!

John F. Brock

 

 

Letter to the Editor

 

Comments on “The National Map―USGS and ACSM,” by Gunther Greulich