Laser scanners, drones and digital photogrammetry: the integration of BIM in surveying technologies
The digital technologies in a BIM workflow that are changing and the entire construction industry: laser scanners, drones and digital photogrammetry used in surveying tasks
In recent years, the evolution of technological tools in professions has led to major innovations, especially in the field of building surveying activities and topography: just consider the significant advantages (precision, time, costs) that can derive from a having a laser scanner connected to a drone to carry out a topografic land survey.
The interesting aspect is that these advantages are accessible to everyone in the building and construction industry because the software tools, which allow to reconstruct the three-dimensional mesh from the photographs, are becoming less expensive and also increasing in terms of performance and data processing speed.
We are now assisting a new technological shift in which dedicated software can convert the data collected from laser scanner and photographic devices into point clouds, three-dimensional meshes, Digital Elevation Models (DTMs) and geo-referenced orthophotos.
The kind of information that allows you to get everything you need to survey buildings, design new infrastructures or deal with their maintenance.
Let’s see the operational principles of these technologies.
Surveying of buildings
It goes without saying that the construction industry in terms of new buildings is at an all-time low. This has led to an increase in renovations and re-modelling projects that require precise survey data of the property to be able to deal with the design phase starting from a detailed knowledge of the structure. The designer can therefore concentrate on the project in the best possible way and make informed choices, optimize spaces. Having precise survey data also leads to more precise cost estimating information too.
Until some time ago, building survey operations were performed with simple tools that weren’t capable of producing a 3D model of a building. The measurements taken to generate the floor-plan of a building were very often horizontal sections taken at a certain height and didn’t take into account any geometric irregularities or any static anomalies of the floorings, etc. Even if a 3D model of the building was defined, this was obviously biased by a series of approximations and errors.
Today, new technologies allow to combine metric, photographic, thermographic information, etc. thanks to the use of laser scanners and drones.
The designer works directly on the structure, getting precise feedback in terms of shape, dimensions, materials, critical situations that could cause injuries or dangerous working conditions, etc.).
All for the benefit of a very high level of design.
Digital photogrammetry
Digital photogrammetry
Architectural photogrammetry is a relevant technique. It allows to acquire metric data of an object (form and position) through the acquisition and analysis of a pair of stereometric frames.
The relief with architectural photogrammetry involves two phases:
- shooting, whose product is the pair of stereometric frames. The object is photographed with the stereometric camera or with the metric camera, placed in two distinct points and chosen respecting the artificial stereoscopy.
- return, which uses the pair of stereometric frames. With this operation it is possible to detect the dimensions of interest, or simply draw a representation of the acquired object.
Digital photogrammetry is a survey technique that generates metric and geographic information including shape and position of three-dimensional objects, such as land plots and buildings, by processing digital photographic images.
The application with drones (aerofotogrammetry) operates through the creation of digital terrain models and orthophotos. It also produces architectural surveys of infrastructures and buildings for the creation of 3D models.
Currently, aerofotogrammetry represents one of the most reliable, economic and precise data terrain data acquisition techniques, useful also in the analysis land mutations in a given territory.
The photogrammetry with drones has different technical applications: orthophotos, geological surveys, drone based topographic services, 3D models (reconstructions of point clouds, contour line processing), mapping of construction sites and territories, rendering of buildings, monitoring of sites with hydrogeological instability, DEM (Digital Elevation Model).
From a series of digital images it is possible to obtain a three-dimensional surface model. The data source can be multiple and the main ones are:
Laser scanners
Laser scanners
The laser scanner measures, in a region of space and according to a predefined density, the positions of points of the objects present.
A point cloud is generated, that is a set of points with defined coordinates in space. From the point cloud, you can define surfaces consisting of triangles (mesh) and continuous surfaces (nurbs). Surfaces can be photorealistic.
Born for industrial applications, the laser scanner is a mechanical electro-optical device that, through the following scanning technique, allows to automatically detect an object in its three dimensions.
The three-dimensional survey provides four information: the three coordinates of the detected point and the value of the reflectance, which changes according to the nature of the material.
The Reflectance characteristic represents the bodies’ ability to reflect the laser beam, indicating for each point of a surface of opaque material, hit by a light ray,
- the response factor, ie the dimensionless relationship between the irradiance, or incident radiant flux density
- the emittance, or outgoing radiant flux density.
Whatever the laser scanning technology used (in the architectural field the most advanced is the phase scan), the result is a very dense cloud of points from which it is possible to obtain an impressive amount of data and process:
- 3D models of buildings detected
- 3D models with surfaces or meshes
- Orthophotos of facades and elevations
- Cross-sections and floor plans
- Virtual browsing within the point cloud
- Implementation in digital environments and AR software (Augmented Reality)
- Implementation in BIM (Building Information Modeling) environments for rapid modeling of the actual state.
The result can also be integrated with GNSS technologies for cloud georeferencing, with aerofotogrammetric surveys from drones for building roofs and any other pre-existing digital survey.
Digital video
The possibility of using a professional video camera to obtain a survey makes this technology easy to use and diffuse, with the advantage of being able to quickly detect even very large areas. The portability of the devices and the autonomy make these instruments very suitable for surveys in areas not easily accessible.
Digital photographs
Being able to use a digital camera as a relief tool makes this technology even easier and more accessible. The main advantage is undoubtedly that of achieving low-cost three-dimensional photogrammetry.
Point cloud: what is it?
Point cloud
When performing a scan, the laser scanner records an enormous number of data points returned from the surfaces being scanned. These can include walls, windows, ducting, steel structures, etc.
The point therefore is the fundamental entity on which the photogrammetric survey method is based.
This data returns a point cloud, composed of x y z coordinates, which can be viewed directly on a computer monitor as a “three-dimensional photograph”, made up of millions of points. These describe the surface of the detected object in detail and the dimensional and colorimetric information can also be obtained.
Simplifying, we can compare a cloud to a 3D mass made up of small droplets.
These points, in addition to their precise spatial coordinates, also have RGB data, deriving from the scanning camera.
Data management
The scans are imported into the modeling software. The individual scans are then filtered in order to remove noise signals that could generate incorrect 3D coordinates and therefore, unwanted points.
Next step is to move on to the processing data through appropriate editing tools, which allow you to manage thousands of points arising from the digitization process. The point cloud is transformed into splines, surfaces and meshes.
Once the data processing phase is completed, we can then use the model to:
- take measurements
- produce video;
- obtain corrected images;
- export cross-sections obtained in DXF format;
- place the detected object according to topographic references;
- create BIM Models.
Point cloud data management software are continuously evolving in terms of calculation performance. In fact, structure from motion technology (SfM) is constantly improving algorithms making it possible to create three-dimensional models of a car by simply taking photos with a smartphone and with remarkable results.
