A significant change took place at the start of 2023 that could impact your survey work, both in the office and the field. The new rule states:
The United States will retire the use of the US Survey Foot and unilaterally adopt the International Foot as the standard of survey measurement.
US Survey Foot is Retiring, US Will Use International Foot
Up until now, only five states have utilized the International Foot. The US Foot is a ratio and doesn’t offer an exact conversion like the International Foot. From a geodetic perspective, this new standard is expected to enhance accuracy. The International Foot is 2 feet per million feet longer than the US Foot, allowing for a focus on coordinates rather than job size.
Let’s explore how the International Foot can affect your survey work and how to smoothly transition to the new standard, both in the field and the office, by following best practices.
Understanding the Impact
When working with state plane coordinates, the coordinates of our work often range between 2-4 million feet. Changing the unit type can result in a 2-foot shift per million feet in both north and east grid directions without affecting elevations.
Consider a job started with a US Survey Feet point at N1,000,000 E1,000,000.
Now, when the units are changed to the International Foot, the entire job experiences a 2-foot shift in the coordinates.
It’s crucial to have best practices in place to ensure a smooth transition and prevent rework, given the significant impact of unit changes on your jobsite.
Best Practices for a Seamless Transition
- Clearly State Units: Include unit information in the early pages of job plans for easy identification.
- Consistent Unit Use: Ensure all parties involved use the same units. If everyone sticks with US Feet, you can localize and continue.
- Verification Control Points: Have control points on the job during model building. These points act as a definitive test for the correct units.
Best Practices Moving Forward
In the Office:
- Verify units using control points before sending the job to the field.
- If changing units, export all job files after the shift.
- Add a suffix indicating the unit type to the job file for clarity.
- Send emails confirming project units during the model-building process.
- Understand how your software handles unit shifts.
In the Field:
- Know your units and avoid changing them between data collectors and machines.
- Calibrate the job with the units used by everyone.
- Check in at a known point for verification at the start of each day.
If you have any uncertainties regarding the new survey measurement standard or 3D modeling for machine control, feel free to reach out to TOPS for assistance.