## IntroductionThe key to transforming any data from one coordinate system to
another coordinate system is having some coordinate values for the same
points (typically 2-5) in BOTH coordinate systems. In our case, we want
to transform survey data in un-projected assumed Cartesian coordinate
space to real world projected coordinates (NAD 83 UTM Zone 12 N), and we have
three benchmarks to do it. The benchmarks were surveyed in with both a total station (very precise: +/- 5 mm) in an assumed coordinate system, and in real world coordinates with a very inaccurate hand held GPS (+/- 5 m). However, using the GPS coordinates as a basis for a simple affine
transformation (i.e. a shift, rotate and datum adjustment), these
coordinates will be good enough for GIS overlay purposes. The cartoon
below illustrates conceptually the process of shifting and rotating the
total station survey data using the GPS coordinates of the same points.
In the example below, BM3 is used as the point around which the
transformation is based (click on image for larger view). You will use
the CHaMP Transformation Tool to help you. ## Download & Look at GPS DataDownload ## Install CHaMP ToolbarInstall CHaMP Transformation Tool Add-In (download here; installation instructions here). Make sure you do not have ArcGIS running when you install the Add-in and download the correct version (10.0/10.1). ## Get Map Document Ready to GoStart a new empty ArcMap Document and get oriented. ## Apply CTT to Unprojected DataYou can follow the CTT example here (using your data instead) to transform the unprojected data into projected coordinates using the CTT. Choose the best transformation parameters based on a combination of visual inspection and minimization of residual errors. Alternatively, the video below shows you how to do the same thing, but with the same data you're working with. Remember to take a measurement between CP1 and CP3 to verify that the intrinsic accuracy of the data hasn't been destroyed in the transformation. Make note of your residuals for your submission. |

Assignments > Labs (4930/6920/6915) > Lab 02 - Coordinate Data, Projections & Transformations >