After several months using a pre-production Topcon GLS-2000 laser scanner, we now have a full production model and have used it on a couple of medium-sized projects already, as well as some interesting tests. As the hardware for collecting large clouds of point data become more and more similar, the focus (pardon the pun) is shifted onto what one actually does with the data. Our next post will look at one of the big challenges with point data – vegetation removal in densely wooded areas.
Back to the GLS-2000 – imaging using the onboard camera on the pre-production model we had was in need of improvement and thankfully the units shipping now are greatly improved thanks to manual exposure control before each scan, fine tuned via a live video feed on the scanner’s integral colour display.
One of the USPs of the GLS-2000 is that it has a switchable laser source (Class 3R for high speed general use, and Class 1 if you fancy a bit of eye-safe scanning on highways) and two cameras. The external super-wide camera is used for general RGB acquisition, taking around a minute to capture a full dome, and the internal co-axial telephoto camera is what the rest of this article is about.
Until now, we had only used it for targeting purposes where the scanner presents a live feed from this camera when doing target scans of prisms. Whilst set up on the last scan of a large job in Cardiff City Centre, we decided to give it a go as the source of images for a medium range scan of the Radisson Blu building. Here are the results:
The GLS-2000 has several pre-configured scanning modes in its options screen. For this building which was a horizontal distance of 124 metres away from the scanner, we used 3.1mm @ 10m / high speed mode which took (with images) just under five minutes. Rather than full dome scanning which was not necessary, “window” mode was used by defining a scan box top-left and bottom-right
So all in all, the test confirms that the internal camera of the GLS provides a very good option for high resolution image capture of windowed subjects. The time to capture a full 360 with the tele camera would be prohibitive, however a lot of the time these types of surveys have a specific purpose i.e. one building elevation. It is important not to discount the data in the surrounding environment – not least because this could be used for cloud to cloud registration. In which case, a High Speed dome scan without images could be acquired for registration / context purposes in under two minutes, so not too much of a hardship!