Beneath Stuttgart's surface: How an ancient sandstone cave was precisely measured and digitally reconstructed using 3D laser scanning
Surveying a cave is one of those rare projects that combines technology, geology, and precision in an extraordinary environment. In Stuttgart, there is an old sandstone quarry whose geometry was completely digitized back in 2013. Twelve years later, this data is playing a key role in legally dividing the cave and preparing for future construction work.
This report shows step by step how such a project is technically implemented—from the initial data collection to the physically visible boundary marker deep underground.
2013: The cave becomes a digital twin
In 2013, the cave was equipped with a Leica ScanStation P40 3D laser scanner systematically recorded. This device emits laser pulses, measures their transit time, and uses this information to generate a high-density point cloud—millions of precise measurement points that describe the entire interior geometry of the cave.
The result is a digital twin, an exact replica of the cave with all its shapes, niches, uneven surfaces, and cavities. On this basis, important calculations could already be carried out at that time:
- Volume of the cave
- Structure and progression of the chambers
- Geometric features and potential instabilities
The data was then processed using special software and converted into a complete 3D model transferred.
2025: The cave must be divided – a very special kind of surveying problem
Twelve years later, the cave once again became the subject of a complex surveying project. Two owners have different goals:
One is planning a backfilling his half, the other wants his half maintain in its current state.
Since the cave is a contiguous space, the proportions must be not using straight lines, but rather on the basis of the natural volume be separated. An unusual surveying scenario:
- How do you divide a cave into two equal parts?
- How do you define a boundary in an irregularly shaped cavity?
- How do you physically transfer this virtual boundary to the real cave space?
Precise volume calculation based on the 3D model
The historical model from 2013 forms the basis for the current analysis.
The first step is to total cave volume calculated mathematicallyNext, an area corresponding to exactly 50% of the total volume is defined in the digital model.
This new virtual boundary is not based on straight lines, but follows the actual shape of the cave. This means:
- The border can be curved, angled, or structurally complex.
- It runs where the geometric division of the interior is exactly halved.
- The resulting borderline is a three-dimensional intersection surface within an irregular body.
From digital space to real cave: transferring the boundary
Once the virtual boundary has been defined in the model, the crucial step follows: the Transfer of digital coordinates into real space.
For this purpose, the geodata is converted into a Tachymeter fed in – an instrument that measures angles and distances with high accuracy. Point by point is then marked in the cave on site.
Along these points, the following will be done:
- iron bars set
- with one visible band connected
- connected to a clearly recognizable physical boundary line
This line shows exactly which part of the cave may be filled in and which part will remain intact.
Why this project is so remarkable from a technical perspective
Surveying a cave poses particular challenges:
- Irregular geometries
Caves do not have clear edges, surfaces, or symmetries—calculating exact volume proportions requires complex 3D analysis. - Long-term digital data
The fact that measurement data from 2013 can be reused in 2025 demonstrates the value of accurately collected geodata and its long-term usability. - Legal relevance
Defining boundaries in an underground space requires the utmost precision, as they are directly linked to property ownership. - Technical precision in the field
The transfer of a digitally idealized boundary line into a real cavity is a high-precision process that requires absolute care.
Precise surveying provides clarity—even deep underground
This cave project in Stuttgart impressively demonstrates how geodesy combines technical precision and complex spatial analysis.
A decades-old cave is completely digitized using modern laser scanning technology, mathematically analyzed, and finally measured in such a way that even a complicated division of ownership can be realized with precision.
Whether for planning, security, documentation, or legal clarification:
Without precise measurements, there would be no reliable basis for decisions in the depths of this cave.