A simple, interactive GIS tool for transforming assumed total station surveys to real world coordinates - the CHaMP transformation tool

摘要

Increasingly, geoscientists and biologists are monitoring the natural environment with total station and terrestrial laser scanning surveys. Due to the remote nature of many of the sites monitored (e.g., streams, rivers, glaciers, etc.) the surveys are often done in unprojected, Cartesian, local, assumed coordinate systems. However, without the survey data projected in real world coordinates the range of possible analyses is limited and the contextual power of existing imagery, elevation models, and hydrologic layers can not be exploited. This requires a transformation from the local assumed to the real world coordinate systems. We present a simple interactive interface, as an ArcGIS Add-In, that allows a user to transform unprojected total station data into real-world coordinates using three benchmark coordinates, which can be collected from a hand-held GPS. Unlike most transformations built into GIS programs, our tool uses an affine transformation (simple shift and rotate) to preserve the precision and relative accuracy of the total station survey, while leveraging the absolute positional accuracy of the hand-held GPS to place one's data approximately in real world coordinates for GIS overlay purposes. The user can quickly visually inspect between six and twelve transformation options, while comparing the residual error estimates to interactively choose the most reasonable transformation. The tool provides an easy-to-use, cost-effective workflow, which facilitates the sharing and visualization of precise total station survey data in real world coordinates through a webGIS or virtual globes (e.g., Google Earth, NASA Whirlwind). The tool has been tested and was used by 12 crews to transform topographic total station surveys of 364 sites into real world coordinates as part of the Columbian Habitat Monitoring Program (CHaMP).