GPS Is Not Magic Underground
Satellites cannot see through concrete. Stop forcing crews to lock GPS pins in tunnels. It fails, it blocks work, and it creates false data.
The Locked Door
We had a ticket system for a subway extension project. The developers added a feature: “Geofence Enforcement.” To open a Work Permit, the user had to be within 50 meters of the zone center.
The crew went down the shaft. They walked 200 meters into the tunnel. They tried to open the permit. The app spun. It searched for satellites.
- “Location not found.”
- “You are not on site.”
The crew was standing on the tracks. They were staring at the workface. But the satellites couldn’t see them. The software decided they were not there.
The software refused to open the form. The crew had to climb back up the ladder (30 minutes). Open the form on the surface. Climb back down (30 minutes).
One hour of production lost for six men. That is six hours of wages burned. Because the software thought it knew better than the human.
The Bottleneck: Blind Faith in Satellites
GPS is a miracle. But it is weak. It needs a line of sight to the sky. Concrete blocks it. Steel scatters it.
When you build strict logic on weak signals, you build a bottleneck. You are telling the worker: “The sensor is the truth. You are the liar.”
This creates Friction. It forces the worker to fight the tool. I have seen workers stand in the rain, waving their phones in the air, trying to catch a signal just to click “I am here.” It is humiliating.
The Pipe: Trust, Verify, Override
We need a sturdy pipe. The data must flow, even if the satellite is blind.
We changed the logic to “Soft Validation.”
- Attempt Capture: The app tries to get a GPS fix.
- Fail Gracefully: If the accuracy is poor (>50m) or the signal is missing, do not block the user.
- Manual Override: Allow the user to drop a pin manually on the map, or select their Zone from a list.
- Flag It: Mark the record as “Manual Location.”
Now, the work continues. In the office, we can see the data.
- 90% of records have high-accuracy GPS.
- 10% are manual.
We look at the manual ones. They are all in the tunnel. This makes sense. The data is valid. The truth is preserved.
Do Not Automate Trust
There is a trend to use technology as a leash. Managers want to know exactly where everyone is, every second.
This is not operations. This is surveillance.
If you design software that treats every user like a potential liar, you will get malicious compliance. They will find ways to cheat the system. Or worse, they will stop using it.
Build tools that help them prove their work. Do not build tools that interrogate them. If the GPS says they are in the ocean, but the photo shows the basement, trust the photo. Trust the human.
FAQs
But we need to prevent fraud. They could be at home.
If you do not trust your team to be on site, you have a hiring problem, not a software problem. Do not use software to police adults.
Can't we use Bluetooth beacons?
We can. They are expensive. They run out of batteries. They get stolen. Sometimes the simplest tool is a drop-down menu.
What is GPS Drift?
Signal bounce. In a city canyon or deep pit, the signal reflects off walls. The blue dot jumps like a scared deer.