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Transformation Tool

The Transformation Tool converts coordinates from an assumed local coordinate system into a real-world projected coordinate system. This allows the data to be geo-referenced with other GIS data. The standard use for the Transformation tool is for processing initial visits to a site where the data were collected in an assumaed, local coordinate system, along with some reference such as GPS coordinates.

How do I know if my survey is already projected?

If either of these conditions are true, then your data is projected:

  • The survey is a repeat survey, and:
    • The total station must have successfully reoccupied the established control network.
    • The data are in UTM coordinates (i.e. x,xxx,xxx , xxx,xxx) instead of an assumed coordinate system (i.e 1000, 2000)
  • The survey is generated from RTK GPS or LiDAR (Initial or Repeat).

If the survey is already projected, then proceed to the next Tool. DO NOT USE THE TRANSFORMATION TOOL WITH ALREADY PROJECTED DATA.

Steps - Projecting Initial Visit Survey Data

  1. Add Base Imagery to your Map. The Coordinate Transformation tool is designed to work with aerial imagery as a base image on your map. There are two ways to do this:

    • Strong Internet Connection: Click the small arrow next to the Add Data to Map button and select ‘Add Basemap’. Select ‘Imagery’ and a background image should be added to your Map Window.

    • No (or slow) Internet Connection: Use the “Add Data” button to add a local raster dataset to the map.

      CHaMP laptops have NAIP imagery preloaded in C:\Base\_Imagery. The images are organized by county.

Transformation Tool Window #1

The first page of the transformation tool sets up the projection and coordinate information for the benchmarks you will use to transform the data.

Output Coordinate System:

  1. Specify the Coordinate System
  2. The Transformation input should populate automatically. If not, choose NAD\_1983\_To\_WGS\_1984\_1.

Coordinate Entry:

We strongly recommend loading benchmarks from the .csv to avoid transcription errors. The Benchmarks.csv file is automatically generated by the CHaMP iPads and should be available after you have connected the iPad to the laptop.

  1. You can enter benchmark coordinates manually from field notes, or Load the Benchmarks from the provided csv file.
  2. If you load from the .csv file, a new window will appear after the file is selected.
    1. Check the “Use Benchmark” box next to three of the benchmarks that you will use in the transformation.
    2. Click OK
  3. Make sure the Projected radio button is selected.
  4. Output workspace:
    1. Make sure that the correct Survey GDB (specified by the current project) is set as your Output Workspace.
  5. When all of the information is properly selected, the ‘Select Inputs’ button will become active. Select it to proceed to the next screen.

Transformation Tool Window #2

In this screen you will select the input data to be transformed with the benchmark information that was selected on the previous screen.

  1. Input Data to be Transformed to UTM
    1. Control Points: Control\_Point\_Unprojected should be automatically set.
    2. The tool should find and list all of the Feature Classes in the Unprojected Dataset in the survey Geodatabase. If only one or two feature classes are listed, you may need to close out of the Transformation tool and select Coordinate Transformation from the Topo Processing menu and double check your input data and specifications.
  2. Choose BMs From Control Point File:
    1. Attribute Field: Set to DESCRIPTION.
    2. Select Hinge Point: Choose the Benchmark you are most confident with. The tool will select the elevation and coordinates from this benchmark to project the survey data. You will get a chance to review all projections from benchmarks on the next screen.
    3. In the drop down menus next to each benchmark and select the appropriate code for each benchmark. The benchmark numbers loaded from the csv file appear in the parenthesis for each benchmark.
  3. Choose Rotation Method: Once the benchmark hinge has been selected, the Rotation Method section should become active.
    1. Select one of the Rotation methods. It doesn’t matter which one, as this will be reviewed on the next screen.
  4. When all required information has been filled out for this screen, Proceed to Transformation will become active. Click on Proceed to Transformation to continue to the next screen.

Transformation Tool Window #3

In the final page of the Transformation Tool, you will visually inspect the different transformations and select the best one available.

  1. Review the Transformations:
    1. Cycle through the various Transformations by clicking through the different options. Watch what happens to the survey in the Map Window.
    2. Visually compare each survey to the base imagery and determine which transformation aligns the survey the best with the base imagery.
    3. Check the values listed in the Residual Error columns. Values closer to zero indicate a better fit and are more desirable. Try to pick a transformation with average/overall low values.
  2. When you have found the best Transformation for the data with the best visual alignment with the imagery and best average/overall low residual error, click on the two confirmation checkboxes.
  3. Click on the “Save to File and Exit” if you are finished.
  4. The survey data is now projected and is added to the map. You may now proceed with checking the survey data for errors.

Troubleshooting

See the CHaMP Coordinate Transformation Tool website.

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