Mapping South Africa with twice the performance

Author:体育nny 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 million 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 newLeica DMC III机载数码相机，基于所有专门针对机载应用程序设计的新CMO技术。作为Leica Realworld大面积空降构成捆绑包的一部分，该传感器将世界上最大的单个框架与最有效的后处理工作流程HXMAP结合在一起，对于此类项目至关重要。该解决方案提供了前所未有的图像质量和整体传感器的无与伦比的几何精度，该传感器使Geospace International能够使用最新技术执行新的25 cm GSD收购。

“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.

表演两次

Geospace International is operating an Aero Commander 690B twin turbine aircraft. The team consists of two pilots and two camera operators.

“轻加权的Leica DMC III使我们每天增加1.5小时的飞行时间。以前，我们不得不回来加油，对成本和时间产生影响。”雅各布斯说。

额外的燃料使Geospace International每天都可以覆盖更多的区域。DMC III的平均每天飞行时间为5.1小时和高性能，HXMAP的处理doubled the performance.

“现在，我们可以使用Leica DMC I以25 cm GSD的速度与Leica DMC III一起以50 cm GSD的速度飞行相同的工作，并以5％至10％的额外飞行时间飞行。在山区，我们飞行的飞行线数量与50 cm GSD的DMC I相同，以25 cm GSD覆盖该区域。

“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,”雅各布斯说。

Unprecedented productivity

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,”雅各布斯说。