A process to graphically demonstrate distance errors associated with local ground-based coordinate systems

This paper describes an empirical process for graphically illustrating, on any project, and using any particular distance accuracy specification, boundaries where significant errors could be introduced in derived ground distances as a result of using local ground-based coordinate systems. The process involves selecting three-dimensional points across the project site, replacing their heights with combined scale factor corrections, and creating contours to represent potential distance errors. The resultant contour map shows potential distance errors in parts per million, which, for comparison with accuracy specifications and practical deliberations, are considered millimetres per kilometre. The effectiveness will depend on the spacing of the selected points and the topography of the project site, but on most projects today closely spaced three dimensional points are readily available. The benefits were demonstrated on an example site, with the conclusion that the process is robust and effective, and will have applications on many large scale civil construction sites, residential estate developments, and other surveys where local ground-based coordinate systems may be used