Correcting Features Captured with an Approximate Base Position - ArcGIS Pro

The approximate base position workflow is useful for capturing data quickly in a location with no known positions. It allows the user the ability to collect field data during the base RINEX data collection saving the time usually required to set a known base position.

Overview of the field data collection

1. Setup the the base station at the data collection site.
2. Set an approximate position using the FastRTK web interface and note the coordinate used.
3. Start RINEX data collection and let it run for the duration of the field data collection and no less than 2 hours.
4. Capture the field data.

The resulting data has the precision of RTK but is not accurate to the datum. In other words the data is shifted by an unknown direction and distance. Usually ~2 meters in any direction. All points will be shifted by the same direction and distance. 

Correcting the data

The data needs to be shifted in the direction and distance between the approximate coordinate and the post processed coordinate.

Create CSV file with the approximate and post processed base coordinates

1. Download the RINEX data file from the base station and submit to OPUS or another post processing service.
2. Create a new Excel or CSV file with the headers Name,Latitude,Longitude,Altitude.
3. Insert the approximate base position into the first row of the file.
4. Insert the post processed coordinate into the second row of the file.

Add CSV file to an ArcGIS Pro Map

1. Create a new ArcGIS Pro project.
2. Click on the Map tab then click the down arrow below the Add Data button.
3. Select XY Point Data.
4. Set the Input Table to the CSV file generated in the previous instructions.
5. The X Field and Y Field should automatically be selected as Longitude and Latitude.
6. Set the coordinate system to GCS_NAD_1983_2011. This is correct for the majority of data collection in the United States.
7. Click Run.

Add Field Data to the Map

1. Click on the Map tab then click the Add Data button.
2. Select your GIS dataset which was captured in the field using the base station. The rover data.
3. Add it to the map.

Shift the Data

There are multiple ways to shift data in ArcGIS Pro. We are going to use the Move tool.

1. Using the Select tool in the Map tab under the Selection section, click and drag a selection box around all of the points to be shifted.
2. Add the approximate base coordinate point to the selection by holding the shift key and selecting it the same way.
3. Zoom into the 2 base coordinates.
4. Click and drag the approximate base point and snap it to the post processed base point.

All of the selected points will be shifted in the same direction and distance. The data is now corrected and accurate to the NAD 1983 (2011) datum.