Journal of Surveying Engineering

The azimuth of a line is a 2-dimensional (2D) phenomenon whose meaning is determined by its circumstance. With the advent of global positioning system (GPS) surveying and making spatial data computations in a 3D environment, it is convenient to compute azimuth as the arctan(Δe/Δn) where Δe and Δn represent local geodetic horizon components of a 3D vector (GPS baseline) defined by ΔX/ΔY/ΔZ geocentric coordinate differences. This paper describes the geometrical characteristics of such an azimuth, proposes it to be called the 3D azimuth, and shows how the 3D azimuth is related to a geodetic azimuth.

Coordinate transformation is the process of determining and applying the relationship between two sets of coordinates. It answers the following question: “I know the coordinates of a point on one data source, what are the coordinate values for this point on another data source?” In most cases, points do not have homogeneous accuracies; thus, they must be weighted according to their relative values. An important objective of this procedure is to keep it as simple as possible so that it can be easily adopted by professional land surveyors or geographic information system (GIS) technical staff. Another important objective of the coordinate transformation process is to make it statistically sound. A weighted least squares is probably one of the better solutions for the transformation problem. Weighted least squares-based coordinate transformation has many applications in surveying practice. One application is to compute NAD83 coordinate values for points with known coordinate values in another plane coordinate system such as NAD27, UTM or NAD83 (19xx), where “xx” is the year in which the adjustment was computed. Another application is to combine maps from different sources or to register a map to an orthophoto when building a GIS. A third example of an application is to sort out evidence in boundary surveys.

The global positioning system (GPS), satellite altimetry, tide records, differential leveling, and a geoid model have been used to study the height system of Taiwan, Republic of China. Using the International GPS Service (IGS) orbit, the geocentric coordinates in International Terrestrial Reference Frame (ITRF) and the mean sea levels at six key tide stations around Taiwan were determined by GPS, and this result will contribute data to the permanent service of mean sea level. It is found by detailed field work and calibration that the vertical datum of Taiwan is defined to be the mean sea level of Keelung located at northern Taiwan. The vertical datum undergoes a secular rise at 1.28 mm/year which must be considered in defining future benchmark heights. It is shown that a good geoid model can be of many uses such as GPS leveling, detecting systematic errors in a leveling net and changes of benchmark heights. The relative sea surface topography (SST) values at tide stations were determined from satellite altimetry and GPS data, and their standard errors are mostly below 10 cm. The SST values are recommended to be used as weighted constraints in the adjustment of a leveling net. A preliminary connection of Taiwan's vertical datum to other regional datums has been examined by computing a global SST at a 600-km wavelength using the EGM96 geopotential model and TOPEX/POSEIDON altimetry.

This paper presents a new approach combining photogrammetry with geodesy for solving the problem of monitoring deformations of a descending gas pipe of a large iron-smelting blast furnace. Owing to the limitation of access available in the area, the monitoring could not be conducted by using geodesy or photogrammetry independently. In the new approach, photogrammetry is used for gaining a single image of the gas pipe, and geodesy is employed for determining the scale of the image. In addition, for designing a concrete support to prevent the gas pipe from breaking down, an approach for determining the coordinates of the central axis of the gas pipe is introduced.