Preserving Romania’s speleological heritage with point cloud and GNSS data

Author: George Damian, Renata Barradas

3D laser scanning provides a high-resolution, non-invasive documentation method to understand natural and cultural sites and manage its exposure to natural and man-made threats. Researchers in diverse fields are unlocking numerous applications using this technology, just like speleologists who are using laser scan data to study and measure caves with millimetre-level accuracy in a non-intrusive way. Point cloud data allows experts to extract cartographic information and calculate areas and volumes to study the evolution of topographic and bathymetric features in caves.

To preserve and understand Romania’s speleological heritage, Top Geocart, the Leica Geosystems’ dealer in Romania, laser scanned the Meziad Cave, a 6,298-metre natural wonder in the western Carpathians. The Meziad Cave, the first cave adapted for tourism in Romania, is known for its spectacular subterranean landscapes with beautiful speleothems (stalactites, stalagmites, columns and curtains). The cave is also home to one of the largest colony of bats in South-East Europe and microscopic endemic organisms (some of them confined to the Meziad Cave).

This high-resolution 3D documentation aimed to accurately capture the site’s complexity and to introduce positive conservation measures to maintain or restore the site before conducting any archaeological and palaeontological invasive research that can modify the original site. Moreover, Top Geocart created 3D models and other deliverables to enable its customer, Spelemat, to store, organise and retrieve information for further analysis. The data provided documents and records the in-situ state of this natural and cultural heritage.

A mission inside the cave

Together with specialists of Spelemat, Top Geocart designed the project and planned for this mission inside the earth. This group of specialists, who understand, respect and promote the use of techniques and geospatial data, collected field data without impacting the environment. Besides using non-intrusive/non-invasive techniques, the team also had to consider the right timing to enter the cave as weather and the cave's river flow were crucial factors to succeed in this mission.

Specialists from Top Geocart used best-in-class software and hardware, including:

• The Leica RTC360 3D laser scanner
• The Leica BLK360 imaging laser scanner
• The Leica Viva GS16 GNSS smart antenna
• The Leica GS18 T RTK GNSS rover
• Leica DISTO™ S910

For point cloud alignment, modelling and GNSS network the team relied on:

• Leica Infinity software
• Leica Cyclone REGISTER 360 3D laser scanning point cloud registration software
• Leica Cyclone MODEL
• Leica Cyclone 3DR
• Leica GNSS Spider software

The team scouted the mountain area and geo-referenced it with the GS16 and GS18 T GNSS RTK rovers with real-time corrections from the Romanian National Reference Stations Network (ROMPOS), running on GNSS Spider software. SmartLink corrections were necessary since the mountainous environment with slopes and trees obstructed the area and from time to time GSM/GPRS signal was lost. The capability of GS16 and GS18 T to use the SmartLink Service was key to cover these gaps and always have a precise position. To deliver the most accurate positions, the team also relied on the Leica RTKplus technology in both RTK rovers as it intelligently adapts to changing conditions by selecting the optimal GNSS signals.

In the interior of the cave, the team moved through the river’s water with special clothes and accessories to safely transport the equipment. Inside of the waterproof containers and floating bags, the RTC360 and BLK360 drifted from location to location. Speed and precision are primordial while scanning with a water level above your chest in temperatures below 10 °C degrees.

Geared with the RTC360, the team captured the larger parts of the cave and artefacts, creating coloured 3D point clouds in under two minutes. With a scanning speed of up to 2 million points per second, advanced HDR imaging system and automated target-less field registration in the RTC360, Top Geocart captured the sites of interest inside the cave in two hours at 750 meters per hour.

At the push of a button, Top Geocart captured full-colour panoramic images overlaid on a high-accuracy point cloud for the narrow parts of the cave with the smallest and lightest imaging laser scanner - the BLK360. For those areas where it was not possible to set on a tripod the laser scanners, measurements were made with the DISTO™ 910.

The mission’s deliverables

Outside of the cave close to the entry, the team automatically and seamlessly transferred data from site to office using Leica Exchange, the exchange service provided by Leica Geosystems, reducing time in the inhospitable environment. Transferring the data easily between the field and the office with Leica Exchange allowed experts to perform a first check of the data onsite with Leica DISTO™ Transfer and Leica DISTO™ Plan App. Using Leica Cyclone FIELD 360 Top Geocart automatically pre-registered and aligned scans at the cave's entrance. 

Back in the office, point cloud data from the BLK360 and RTC360 was registered with Cyclone REGISTER 360. The GNSS data was checked and processed with Infinity software, in the GNSS project were imported the DISTO™ data, too. Together with Spelemat, Top Geocart created a unified point cloud, as Cyclone REGISTER 360 project, and exported in E57 and LGS formats to visualise it with JetStream Viewer, a light-weight point cloud viewing tool. The E57 file was imported in Leica Cyclone 3DR to create meshes and compute digital terrain models (DTM) from point clouds.

Experts also created 2D topographical maps and 3D DTM with data from the GS16 and GS18 T RTK rovers to develop new tracks and paths for visitors. Distances and CAD files with 3D points and pictures were extracted from the data collected with the DISTO™ S910.

The data provided will support researchers, tourists and facility managers alike. It will guide feasibility studies for touristic plans and be used as marketing material to invite visitors to explore this natural wonder. Point cloud deliverables provide researchers with a digital twin of the cave where they can extract any profile and 3D measurement. At the same time, GNSS data helped to identify the areas and paths to create access for tourists and scientists.

“Leica Geosystems and Top Geocart provide complete software and hardware set for the entire workflow. The sensors have the capabilities to work in difficult environments and meet the highest standards in measurement excellence. The management and specialists from Spelemat admitted they were capable of working more efficiently and in more challenging environments than ever before,” said Viorel Lascu, cave management expert at Spelemat.

The success of capturing the Meziad Cave convinced Spelemat to invest in RTC360, BLK360, DISTO™ to keep exploring and understanding Romania’s natural wonders.