U.S. tech giant Google has unveiled a prototype smartphone it says creates 3-D maps to help the visually impaired navigate unfamiliar indoor sites unassisted.

Two hundred examples of the prototype smartphone with "customized hardware and software" have been offered to developers interested in creating apps for it.

Sensors in the phone make more than 250,000 3-D measurements per second to update its position in real time and present its location as a 3-D map.

Google's Advanced Technology and Projects unit developed the phone with help from researchers at various institutions.

"The goal of Project Tango is to give mobile devices a human-scale understanding of space and motion," the company said. "We're ready to put early prototypes into the hands of developers that can imagine the possibilities and help bring those ideas into reality."

Google is not alone in attempting to turn technological advances to practical use in every day life in an attempt to attract more customers, tech analysts say.

"The focus is not just on the hardware or the device, but on what the gadget can actually do," Bryan Ma, of U.S. market research firm IDC told the BBC.

"It is all about taking it to the next level of usage -- be it augmented reality, help with basic healthcare or even just creating better maps," he said.