based modelling

RGB point cloud

Laser scanning vs image based modelling

As digital photogrammetric techniques advance at pace, the ability to use them as standalone technologies increases, writes Plowman Craven director Peter Folwell

While having a customary glass of wine in front of the TV one evening I managed to catch two very interesting documentaries — one about the 75th anniversary of the Battle of Britain and the other giving a plotted history of the Ordnance Survey. Each contained items about the important role aerial photogrammetry played in collecting accurate information for mapping; how the technology has changed! This is also very true for terrestrial photography — originally a source of accurate measurement producing photo plans and orthophotos for 2D representation and the use of stereo photogrammetry for the extraction of 3D line work.

The arrival and development of laser scanning technology initially relegated

About the author

Peter Folwell is a director at Plowman Craven with responsibility for survey deliverables within the BIM environment. He is involved in Survey4BIM and a founder of BIMnet.

the use of photography as an accurate source of data. Now considerable technical advances in the use of digital photogrammetry has meant the two technologies are intrinsically linked and provide powerful 3D measurement and data collection solutions

Initially laser scanners collected only 3D data where each of the points had a recorded intensity value, represented by a range of colours dependant on the software or scanner type. To enhance interpretation and become more user friendly it was possible to create a workflow and process to use external cameras.

An early method adopted by Plowman Craven was, after collecting point cloud data, the scanner was replaced with a DSLR camera mounted on a Nodal Ninja capturing photographs covering 360 degrees. The photographs were stitched into a panorama and used for overlaying the scans with RGB information.

Most modern terrestrial scanners now have inbuilt cameras that can provide good quality RGB information for each scan location. Some collect High Dynamic Range imagery — such as the Leica P40 or imager5010C from Z+F, while others

The nctech iSTAR can produce rapid 360 degree imaging of the environment and batch stitch the images together in seconds

have single exposure technology. already very familiar with 360° panora- commonplace in a wide range of sectors

What is produced is a large, high quality ma’s and virtual walkthroughs now including agriculture, mining, military, point cloud data set, RGB enhanced but becoming an everyday occurrence. surveillance and consumer recreation. We needs specialist software and hardware to Systems such as the nctech iSTAR can are seeing real benefits for site investigaprocess, manipulate and view the data. produce rapid 360 degree imaging of the tions, construction program assessments, Because of this, most laser scanning man- environment and batch stitch the images condition surveys and surveying areas ufacturers provide a viewing and interac- together in seconds. which were previously inaccessible. tive capability of sharing scan data with The use of gigapixel imagery is now Plowman Craven has been involved in other stakeholders without having the enabling the user to visualise features in the film and entertainment sector for a need for specialist software or high spec considerably greater detail than standard considerable number of years with experihardware. Leica TruView, Faro WebShare, photography — a fantastic tool for heri- ence mentioned before of working on the LFM NetView are examples of viewers via tage and asset recording. Game of Thrones, Skyfall and Marvel’s web browsers as 360-degree photographi- Image Based Modelling is becoming a Guardians of the Galaxy. It is an industry cally enhanced panoramic views. viable alternative to laser scanning. It is that has fully embraced both laser scan-

Displaying point cloud data in this way definitely low cost, flexible and in many ning and digital photographic techniques. enables a level of interaction and the ability cases more portable. Packages like Pix4D, Multi camera systems enable the to extract measurements. The object/person to be scanned visual quality of the data has the added advantage of providing a great source of asset ‘‘ Image Based Modelling technology is developing in one click eliminating any movement and then a model created, fully textured ready and condition information at a rapid pace and is becoming a viable option for the VFX team or 3D for other applications and in particular the BIM process. over laser scanning but both technologies have printers. This form of tech nology is now readily avail -

The integrated technology their strengths and limitations. able to the general public has moved forward dramatically over the last few years with many mobile mapping ’’ through such apps as Autodesk 123D Catch which can turn ordinary photos solutions now providing Lidar scanners Agisoft, Bentley ContextCapture (see from your mobile devices into 3D objects. with multi camera systems to capture cali- page 19) allows point cloud generation Image Based Modelling technology and brated imagery and point cloud data at the from photographs. The software packag- its application is developing at a rapid same time, while travelling at speed, and es look for common or feature points pace and is becoming a viable option over having the ability to produce the quality extracted from the photographs and then laser scanning but both technologies have and accuracies demanded. results in the computation of the camera their strengths and limitations. The ability

The ability to be able to view, accurately positions and point cloud constructed. to combine them intrinsically, obtain similocate and access large spatial data sets has A popular and growing use of this tech- lar data sets, apply them appropriately is considerably improved the efficiency and nology is with Unmanned Aerial Vehicles where greatest value can be obtained. productivity of GIS data collection. mounted with cameras. UAVs are provid-

As digital photogrammetric techniques ing an economical alternative to other Thank you to Marta Wren at Plowman Craven advance at a pace the ability to use it as a forms of aerial photogrammetry. for assistance with this article. standalone technology increases. We are Reduced cost has made this technology ■ plowmancraven.com