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 you to collect field data during the base RINEX data collection, saving the time usually required to set a known base position.

Overview of Field Data Collection

1. Set up 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 field data collection (minimum 2 hours)
4. Capture the field data

Correcting the Data

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

Step 1: Create CSV File with Base Coordinates

1. Download the RINEX data file from the base station
2. Submit to OPUS or another post-processing service
3. Create a new Excel or CSV file with the following headers:

Name,Latitude,Longitude,Altitude

4. Insert the approximate base position into the first row
5. Insert the post-processed coordinate into the second row

Example CSV:

Name	Latitude	Longitude	Altitude
Approximate	45.00000000	-122.00000000	25.000
Processed	45.00001234	-122.00001234	25.123

Step 2: Add CSV File to ArcGIS Pro Map

1. Create a new ArcGIS Pro project

2. Click on the Map tab

3. Click the down arrow below the Add Data button

4. Select XY Point Data

5. Set the Input Table to the CSV file generated in Step 1

6. The X Field and Y Field should automatically be selected as Longitude and Latitude

7. Set the coordinate system to GCS_NAD_1983_2011

   :::note This is correct for the majority of data collection in the United States. :::

8. Click Run

Step 3: Add Field Data to the Map

1. Click on the Map tab
2. Click the Add Data button
3. Select your GIS dataset captured in the field using the base station (the rover data)
4. Add it to the map

Step 4: Shift the Data

There are multiple ways to shift data in ArcGIS Pro. We'll 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

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.

Visual Reference

The screenshot below shows:

• Red points - Survey points captured with approximate base position (NAD83_2011)
• Green points - Survey points after adjustment (NAD83_2011_Adjusted)
• Red triangle - The approximate base coordinate (BaseCoordinates_XYTableToPoint)

After the shift operation, all red points will align with their corresponding green positions.

Tips for Best Results

Tip	Description
RINEX duration	Collect at least 2 hours of RINEX data for reliable post-processing
Note coordinates	Always record the approximate coordinates used before starting data collection
Same session	All data collected in the same session will have the same offset
Backup data	Save a copy of your original data before performing the shift

Alternative Methods

While the Move tool is the simplest approach, you can also correct data using:

• Spatial Adjustment tools - For more complex transformations
• Calculate Geometry - Apply coordinate offsets mathematically
• Python scripting - Batch process multiple datasets

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