Over the past couple of weeks Blacktown resident Dave Lewis began noticing odd symbols popping up on roads throughout the county.

Most of the time the markings were L-shaped but an occasional V-shaped version would occasionally arise. All of the symbols were painted on the roads with bright white paint that could readily be seen.

On closer inspection Lewis noticed beneath the markings were small numbers painted in red.

As the owner of Blacktown NC LLC, a biomedical company that uses imaging technology, he knew there was some kind of science at work here.

“I knew these were being painted so they could be seen from the sky for some kind of satellite imagery,’’ Lewis said.

Local PennDOT officials also noticed the markings and at first were stymied.

This isn’t a case of crop circle-like markings meant to guide in aliens from other planets. But it is a situation where out-of-this-world technology is at work.

After some quick checking it was found the markings were made by a PennDOT subcontractor conducting aerial surveys of some local roads.

Known as photogrammetry, this science has been around since the 19th century but now has a 21st century technology twist.

Markings are placed on roads which are being surveyed so that they can be seen from an airplane or helicopter.

The markings serve as targets which can be photographed from the air and are used in the survey to provide a network of known positions where global positioning satellites are then used to provide pin-point accuracy.

Such surveys are now being used by the transportation industry, local and state governments along with government mapping systems.

Maps generated by these surveys provide detailed, three-dimensional virtual models of the terrain and surface features allowing engineers to better design roads.

“Somebody, somewhere has determined this area is in need of this survey,’’ Lewis said.