Over the years we have performed dozens of building and industrial plants surveys, using different measuring techniques.
Often we happened to discuss the advantages and disadvantages of the use of more traditional survey methods, such as total station topographic survey integrated with direct acquisition of measurements with portable laser distance tools, compared to the use of 3D laser scanner.
When conducting the survey of a complex architecture, such as an historic building extended on several floors or an industrial plant, the most used techniques usually are:
- Direct survey, performed with portable laser distance meters
- Surveying with total station integrated with direct survey
- Survey with 3D Laser Scanner
In this article we will therefore focus on the pros and cons of 3D Laser Scanner vs. traditional survey techniques.
1. Direct survey with portable laser device
The survey is performed by acquiring the measures directly, distances such as the length and width of a room, the distance from an edge of the room to a door, the height from floor to ceiling, etc. The building being measured is divided into elementary geometries, usually different rooms or areas that compose it, and that will then be measured individually and connected to each other. The connection between the different geometries is performed taking care to detect common elements, which are usually represented by doors or passages between the different zones.
In this case it is very important to measure the thickness of the walls. Using this technique it is useful to try to acquire even overall measures that can be used to double check in the phase of connection of the various areas to increase the overall accuracy of the survey.
This is the least expensive method, as it’s not necessary any particular investment if not for the purchase of a good laser tool, but it is also the least accurate and suitable only for the measurement of simple building, small/medium size and that are developed on a single floor.
2. Topographic survey with total station integrated with direct surveys
This type of survey is suitable if you need to measure and represent real estate complex, with an extension above average, complex geometries that are extended on multiple levels. The survey is performed in two stages, the topographic survey and the direct survey.
In the first stage the surveyors measure with total station the position of a number of significant points, such as the vertices of the property measured, pillars, doors, windows, inner edges of the various rooms etc. These points will be returned with high precision in an overall coordinate system, and may be used to connect the different areas measured by direct method.
In the next step the topographic measurements will be integrated with a direct survey. The geometry of the different areas will be measured without the need to pay special attention to how these will be linked together, as for their global positioning the surveyor will use the topographic survey.
This working method requires an initial investment for the purchase of a good total station, the use of which allows to obtain an accuracy sufficient to definitely most architectural applications and/or engineering for which the survey may be required. However, does not allow to optimize the execution time necessary to measure by hand all the details that your customer needs you to represent.
3. Survey with 3D Laser Scanner
In the execution of a complex survey with 3D Laser Scanner you will not need to worry about run out of details, as the scanner will automatically acquire a so-called ‘point cloud’ with a resolution determined by the surveyor before starting the scan, depending on the size of the space to be measured and the size of the details that you want to acquire. The clouds acquired will then be connected to each other through the overlapping areas acquired from several different station points, using software that perform this type of calculation that is defined in jargon ‘cloud-to-cloud registration’.
The hardware performs a full scan, 360° horizontally and 320° vertically, in a time ranging from 1 to 30 minutes depending on the selected resolution and quality of the data to be obtained. The clouds acquired do not contain color information of the detected object, but only geometric information (X, Y, Z) and the reflectivity of the surface (usually a value from 1 to 100). If you want to get information about the color of the surface and link it to the points, it will be necessary after the laser scanning to capture a series of images through the digital camera that some laser scanners have built in or external camera appropriately positioned.
For surveys of particularly complex or extended properties, you can place on the spot, before the start of the scanning operation, a network of target whose coordinates are measured with a total station, which will serve to the positioning of the scans in an overall coordinate system.This lengthens the time of data acquisition, but avoids the cloud to cloud registration and increases the overall accuracy of the survey.
Using this technology the financial investment is higher, but the acquisition of point clouds allows to obtain a series of advantages, compared to the two previously described techniques, which can sometimes make the difference.
Let’s see them in detail:
- Time spent for data capture up to 10 times faster, then construction/installation stop of shorter duration;
- You can be sure that all the necessary information have been collected, allowing you to avoid the risk of having to return to the site to integrate with new measures;
- There is no need to touch the measured object, which in some cases is not possible or desirable;
- Higher accuracy of measurement, like a survey with total station;
- Using a smaller number of resources in the acquisition phase of the data, then transfer costs lower and greater overall productivity of the company;
- Ability to represent the space detected in an innovative way than the traditional 2D representation;
Against these pros, there are also cons in the use of laser scanner technology, we see them are:
- The need for a rather high initial investment;
- Purchase of new software dedicated at elaboration of point clouds, resulting in specific training period;
- High-end hardware for data processing;