Journal of Surveying Engineering

There are many procedures for adjusting data and detecting the presence of blunders in a set of observations. Most such procedures involve examining the adjustment results for residuals whose magnitude is in some sense “large.” In data snooping, each residual is divided by its own standard deviation, resulting in a statistic whose distribution is known. Thus blunder detection becomes a statistical hypothesis testing problem. In iterated data snooping, only the observation with the largest normalized residual is deleted at each iteration. The residuals may be either from a conventional least‐squares LS adjustment or from an “$L_1$ norm” adjustment that seeks to minimize the sum of absolute values of residuals. Iterated data snooping with the LS residuals is at least as effective as any other method of detecting blunders. We show by example that it can produce much better results than the $L_1$ norm adjustment. Both forms of data snooping are superior to the many empirical or approximate methods that are still widely used.

In traditional underground surveying operations, where a bearing is transferred through a single shaft, only one azimuth of the underground traverse is involved. The use of gyroscopic measuring equipment, however, allows the direct determination of the azimuth of other sides of traverse. Measurement of an extra gyroscopic azimuth allows not only checking the observations of the azimuths and the angles between them, but also reduces the breakthrough error. Determination of the optimal location of an extra gyroscopic azimuth in straight traverse with the sides of the same length assures minimal influence of errors of measurements in the traverse on the value of the lateral component of the breakthrough. In this paper the problem of optimal location for an extra gyroscopic azimuth in straight tunnel construction, in which there is a straight traverse with the sides of the same length, is solved. Analysis of the accuracy effects as well as numerical examples indicate definite advantages in application of optimal technology as compared with measuring extra gyroscopic azimuths in other places. In this work it is also stated that the optimal location of an extra gyroscopic azimuth in straight traverses having sides of the same length is in the third part of the traverse, independent of the accuracy of measurement.

On‐the‐fly resolution of carrier phase ambiguities, which is the key to centimeter‐level accuracy in differential kinematic GPS positioning, is investigated using a high‐precision, single‐frequency, 10‐channel, C/A code receiver. The major characteristic of this C/A code receiver is its narrow correlation spacing, which improves code‐measuring accuracy to 10 cm and reduces code multipath interference. The high accuracy of the code enables the user to reduce the search area containing the correct integer‐ambiguity solution. The principles of the least‐squares search procedure used herein to obtain the correct ambiguity solution are described. Kinematic test results for land are presented for the cases of a benign multipath environment and a comparatively high multipath environment. For the benign multipath case, the correct ambiguities are found within 1–3 min, with a high success rate, under a relatively good six‐satellite geometry (GDOP ≈ 3) and a short monitor‐remote separation (<5 km). In the presence of carrier phase multipath caused by nearby trees, however, the success rate decreases to less than 50% and the correct ambiguity solutions are found only after a significantly longer observation period.

This paper deals with the modeling and solution of an optimal direction observation scheme in two‐dimensional triangulation or triangulateration networks under a given precision criterion matrix of the estimated coordinates. The difficulty in setting up appropriate criterion matrices for the orientation unknowns is overcome by eliminating the orientation unknowns from the adjustment model and equating the variance‐covariance matrix of the estimated coordinates with the given criterion matrix of coordinates. Based on the analysis of the given optimization examples, a two‐step optimization procedure is proposed, which may result in a most economic survey campaign. That is, the optimal solution of individual observational weights for all the possible directions in the network should be explored first, to delete those directions that obtained zero or close to zero optimal weights and therefore have insignificant contribution to the network accuracy. The solution of an optimal group weight for each station in the network is then sought for only those directions that obtained significant individual weights. The obtained optimal group weights of directions are used as a guideline in the choice of instrumentation and operational procedures.