Metro Phase 3 Corridor Survey

The problem

The alignment ran through Marathahalli, Kadubeesanahalli and Bellandur – some of the densest traffic in the country – and the design consultant needed an as-existing corridor model before pier locations could be frozen. A conventional survey party would have needed lane closures on the Outer Ring Road, which the traffic police were never going to approve for a six-week window.

Three quarters of the corridor also fell inside Bengaluru's controlled airspace, under the approach path to HAL and within the Kempegowda green-zone buffer at the northern end.

What we did

Airspace came first. Ananya filed 14 separate Digital Sky permissions covering the corridor in 1.5 km blocks, plus a written coordination protocol with the local ATC for the segments inside controlled airspace. Clearance took 19 days.

Flying was done in the 05:40–07:15 window before traffic built, in 1.2 km segments at 90 m AGL with 80/70% overlap. Kavya's team laid 148 DGPS control points along the corridor overnight, tied to the client's existing benchmark chain, with 31 independent check points held out of processing entirely.

Processing ran in overlapping blocks so a rejected segment could be re-flown the next morning without re-processing the whole corridor.

The outcome

The corridor model came back at 2.8 cm horizontal and 4.1 cm vertical RMSE against the held-out check points. The design consultant used it to shift 11 pier locations before tender, four of which had been sited on top of unrecorded utility crossings that the old drawing set did not show.

No lane was closed at any point during the survey.

“The pier relocation alone saved us more than the survey cost. Having a dated model of what was actually on the ground – not what the 2011 drawing said – changed how the design review ran.”

Rajesh Agarwal, Project Director, Sunrise Infra Projects