Generating megacity-scale building height maps without DGNSS surveyed GCPs: An open-source approach

Abstract

This paper describes an open-source method for generating megacity-scale building height maps without proprietary software or Differential Global Navigation Satellite System surveyed ground control points (GCPs). We use the open-source Satellite Stereo Pipeline (S2P) software along with four scenes of 2.5m resolution Cartosat-1 data for Bengaluru to demonstrate this. Digital Surface Models (DSMs) of 5 m resolution are generated using S2P, and terrain removal is achieved using 30m SRTM data resampled to 5m. The resulting normalized DSM is calibrated and validated using 1270 GCPs. These were generated by counting the number of occupiable floors of buildings and marking zero elevation ground points. The final building height map of Bengaluru covers a total area of about 1420 km2, and across the four scenes, has RMSE values ranging from 2.8m to 3.9m—an error of approximately one floor. Furthermore, we implemented this workflow using stereo imagery for Mumbai, and the RMSE values obtained were comparable to those for Bengaluru. Hence the method we describe is a very cost-effective way of generating megacity-scale building height maps. The height maps generated using this method can be used to better understand numerous urban characteristics including land use intensity and population distribution and can play a crucial role in urban planning and policy making.

Geographic Information Systems for Facilitating Audits of the Urban Built Environment

“…In the other cases, there was a difference of 1 floor. This is acceptable and comparable with other open-source tools that achieve an error of 1 floor in building heights, which is sufficient for most city-scale analysis [52]. Furthermore, a closer investigation revealed that the deviations are attributed to cases in which the ground floor was below street level (for buildings with semi-basements), or to cases in which the first floor is above the street level (for buildings with pilotis).…”

“…In addition, the DTM models may not provide accurate information about the terrain, as sometimes, a building may have a semi-basement floor that is constructed below ground level (or constructed above ground level when the building has pilotis). Nevertheless, the number of floors were accurately estimated for the majority of the buildings in the case study (57%), and for the rest with accuracy of ±1 floors, which is considered acceptable for a large-scale analysis [52]. The building height and the number of floors can also be determined using other methods, including light detection and ranging data with high resolution [59].…”