ERROR ANALYSIS IN SURVEY AND PHOTO GRAMMETRIC PROJECTS

Abstract

The observations, as the recorded values of field measurements, are generally not ready for use without having been processed and analysed. Error analysis of field observa-tions has been a subject of investigation for a long time so as to find out the effect of the errors finally on the comput-ed quantities. The conventional method is limited only to the deter-mination of most probable values and the standard errors of observations. With the availability of digital computing faci-lities, the techniques of analysis have now been extended beyond these and investigations have been done. Having deter-mined the realistic values of observations and their variances and covariances, the reliability of the observations, validity of procedures and assumptions and the confidence one can lay on end results, can be determined by the present error analysis technique. The procedure is divided into three stages : (i)\ Pre analysis - to find out adjusted values (ii) Post analysis - to find error ellipse and confidence region parameters / (iii) Statistical tests - For validity of assumptions and the mathematical model. This error analysis technique has been utilized in this dissertation to investigate the behaviour of errors in common engineering projects involving field surveys and photogrammetric approach. Investigations have been carried out for two specific cases Viz. traversing, a common field survey problem of establishing control points for engineering surveys and photogrammetric generation of control data employ-ing terrestial photogrammetry. For both cases, mathematically generated error free data has been used first and thereafter the error is introduced randomly in the data to examine the error analysis technique. The results obtained include most probable values of observations, their variances and covariances, error ellipsoid and confidence region parameters alongwith statistical tests on variance factor for both sets of data for both problems. 'On the basis of results, it has been concluded that the modern error analysis procedure is both effective and more complete in analysing error behaviour and that the same should be applied in all types of field surveys. Statistical tests on variance factor show that the assumed variance factor is acceptable at the level of signi-ficance a = 0.05.