Mapping South Africa with twice the performance
Author: Penny Boviatsou
More than 90 years ago, National Geospatial Information (NGI), a component of the Department of Rural Development and Land Reform (DRDLR), commenced with the establishment of an integrated survey system and provision of extensive mapping coverage of South Africa.
NGI, is also known as the national mapping agency of South Africa, has the largest and most extensive archive of aerial photography and imagery dating back to 1926 with numerous national coverages. The imagery has evolved significantly over time, and, since 2008, all imagery is acquired with high resolution digital sensors in both colour (RGB) and colour infra-red (CIR).
In 2008, NGI decided to acquire their own Leica DMC I airborne camera system and appoint a service provider to operate the system on its behalf. Geospace International, a leading aerial photography service provider in Africa, successfully tendered and has been appointed by NGI to operate DMC I up until 2016. Geospace International also acquired its own DMC I in 2008 and used both systems for the acquisition of most of the imagery captured for NGI’s national mapping programme.
The mapping program started in 2008 and the aim was to cover the whole country (1.2 square kilometres) every three years at 50 centimetres Ground Sampling Distance (GSD) until the end of 2016. In 2017, NGI decided to start a new cycle of acquisition at 25 cm GSD covering the country. The demand for higher resolution imagery by the users of the data led to the change in resolution.
NGI uses the data to generate 1:10,000 orthophotos, covering South Africa every three to five years with the 25 cm GSD. The orthophotos are used to update the 1:50 000 topographical maps. The orthophotos are also made available at no cost to South African citizens and companies that need to use this data for their GIS or other applications.
A unique solution for wide-area mapping
With the new direction from NGI to cover South Africa with 25 cm GSD imagery from 2017 onward, Geospace International decided to purchase the new Leica DMC III airborne digital camera, based on all new CMOS technology specifically engineered for airborne applications. As part of the Leica RealWorld large area airborne imagine bundle, this sensor combines the world’s largest single frame with the most efficient post-processing workflow, HxMap, crucial for a project as such. This solution delivers unprecedented image quality and the unsurpassed geometric accuracy of a monolithic sensor, which enables Geospace International to perform the new 25 cm GSD acquisitions with the latest technology.
“The complete installation of the Leica DMC III took only three days. Our goal was to acquire 25 cm GSD imagery at approximately the same flying height as previously done with the 50 cm GSD projects using the Leica DMC I, resulting in roughly the same cost per job as before. The Leica DMC III allowed us to do this,” said Bernhard Jacobs, director at Geospace International.
Once Geospace International collects the 25 cm GSD RGB and CIR imagery for NGI, the calibrated imagery together with the post processed GPS/INS data are supplied to NGI. The national mapping agency of South Africa then goes through the process of performing aerial triangulation, elevation capturing and final orthophoto creation, using the Hexagon Geospatial Imagestation suite of products. The software provides high volume photogrammetry and production mapping tools, including project creation, orientation and triangulation from aerial and satellite imagery.
Twice the performance
Geospace International is operating an Aero Commander 690B twin turbine aircraft. The team consists of two pilots and two camera operators.
“The light-weighted Leica DMC III allowed us to add additional 1.5 hours of flying time per day. Previously, we had to return to refuel, having an impact on cost and time,” said Jacobs.
The additional fuel allows Geospace International to cover more areas in a day than before. With an average 5.1 hour of flying time per day and high performance, processing of HxMap, the DMC III doubled the performance.
“We can now fly the same job previously flown at 50 cm GSD with the Leica DMC I, at 25 cm GSD with the Leica DMC III, with 5 to 10 percent additional flight time. In mountainous areas, we fly the same amount of flight lines to cover the area at 25 cm GSD as we would with the DMC I at 50 cm GSD.
“The new DMC III has better overall radiometry and a more homogeneous quality across the complete block. We are impressed with the GPS/IMU results,” said Jacobs.
Geospace has covered more than 240,000 km2 at 25 cm GSD from July to November 2017, close to 50,000 releases, and three months ahead of schedule. The company aims to continue procuring imagery for NGI covering South Africa every three to four years.
“We would recommend the Leica Geosystems products and solutions to anyone in the aerial survey industry because of the quality, the excellent support given by the staff, and the overall durability and long-term use without problems when using the system,” said Jacobs.