What is a point cloud?
Posted: Sun Dec 22, 2024 10:40 am
Having presented his topic, Alexander Korzhov, BIM coordinator at Infrastroyproekt with an education in usa email list applied geodesy, admitted that point cloud modeling for facades and other elements is not really that different.
Content
About laser scanning
About photogrammetry
On creating facade models from point clouds
What's the bottom line?
But before he elaborated on his views, he decided to tell the attendees of the March BIM breakfast how a point cloud can be obtained, the pros and cons of each approach, and what problems can be encountered when creating a 3D model based on this data.
About laser scanning
"Laser scanning is an indirect way of measuring the distance from the laser beam source point to another surface. If you know the coordinates of the radiation source point, then using a direct geodetic problem you can determine the coordinates of the point on the surface of the object," explained Alexander Korzhov.
Among the types of scanning work, he identified two categories:
Airborne laser scanning (ALS)
When using VLS, you can cover a large area, which is ideal for inspecting linear and area objects. And as a radiation source, you can use not only UAVs, but even airplanes and helicopters. The disadvantages of this approach are its high cost and the increased fragility of cheaper radiation source carriers.
Terrestrial laser scanning (TLS)
NLS is great for working both outside and inside the building. The scanning equipment is quite compact and can sometimes be transported directly in the operator's hands. And to start scanning, you only need to have access to the surface being scanned. Among the disadvantages of NLS: the need to purchase additional scanners and auxiliary devices when measuring large and tall buildings, as well as sometimes excessive detailing of objects compared to classic surveying with an electronic tachymeter.
Alexander Korzhov emphasized that, in his opinion, ground-based laser scanning is superior to aerial scanning, since the safety of scanners in ground-based laser scanning is much higher, unlike aerial scanning, during which the UAV can collide with a bird or fly away in an unknown direction.
About photogrammetry
Another way to get a point cloud is photogrammetry, a method of determining the shape and size of an object based on its photographic image. Initially, this image is flat, so to create a volumetric effect, the so-called stereo pair, it is taken from different points and then the pictures are combined in special software. Stereo pairs are then used to create a three-dimensional model.
The advantage of photogrammetry is that a point cloud can be created even using a smartphone. However, to do this, you need to know the rules of shooting. However, to obtain data suitable for use in commercial projects, you certainly need to use professional equipment. But compared to 3D scanners, it is much cheaper.
What is a point cloud?
Alexander Korzhov gave his own definition of the term to the BIM breakfast audience:
A point cloud is a set of information about the spatial position and appearance of an existing object in nature, obtained as a result of laser scanning, photogrammetric survey or surveying with a tachymeter.
The expert also noted that point clouds are a collection of both visible and invisible information, the so-called blind spots. These areas are a significant problem, since artificial intelligence cannot recognize a complete object in them due to the lack of information. That is why when processing point clouds, an experienced specialist is required who can competently process the data manually and supplement it if necessary.
Point clouds can be colored or black and white. According to Alexander, the second option is enough for his work - it contains enough information about the geometry and dimensions of the object needed to build a model. Colored point clouds are also in demand, but less so, since they take much longer and are more expensive to create.
Content
About laser scanning
About photogrammetry
On creating facade models from point clouds
What's the bottom line?
But before he elaborated on his views, he decided to tell the attendees of the March BIM breakfast how a point cloud can be obtained, the pros and cons of each approach, and what problems can be encountered when creating a 3D model based on this data.
About laser scanning
"Laser scanning is an indirect way of measuring the distance from the laser beam source point to another surface. If you know the coordinates of the radiation source point, then using a direct geodetic problem you can determine the coordinates of the point on the surface of the object," explained Alexander Korzhov.
Among the types of scanning work, he identified two categories:
Airborne laser scanning (ALS)
When using VLS, you can cover a large area, which is ideal for inspecting linear and area objects. And as a radiation source, you can use not only UAVs, but even airplanes and helicopters. The disadvantages of this approach are its high cost and the increased fragility of cheaper radiation source carriers.
Terrestrial laser scanning (TLS)
NLS is great for working both outside and inside the building. The scanning equipment is quite compact and can sometimes be transported directly in the operator's hands. And to start scanning, you only need to have access to the surface being scanned. Among the disadvantages of NLS: the need to purchase additional scanners and auxiliary devices when measuring large and tall buildings, as well as sometimes excessive detailing of objects compared to classic surveying with an electronic tachymeter.
Alexander Korzhov emphasized that, in his opinion, ground-based laser scanning is superior to aerial scanning, since the safety of scanners in ground-based laser scanning is much higher, unlike aerial scanning, during which the UAV can collide with a bird or fly away in an unknown direction.
About photogrammetry
Another way to get a point cloud is photogrammetry, a method of determining the shape and size of an object based on its photographic image. Initially, this image is flat, so to create a volumetric effect, the so-called stereo pair, it is taken from different points and then the pictures are combined in special software. Stereo pairs are then used to create a three-dimensional model.
The advantage of photogrammetry is that a point cloud can be created even using a smartphone. However, to do this, you need to know the rules of shooting. However, to obtain data suitable for use in commercial projects, you certainly need to use professional equipment. But compared to 3D scanners, it is much cheaper.
What is a point cloud?
Alexander Korzhov gave his own definition of the term to the BIM breakfast audience:
A point cloud is a set of information about the spatial position and appearance of an existing object in nature, obtained as a result of laser scanning, photogrammetric survey or surveying with a tachymeter.
The expert also noted that point clouds are a collection of both visible and invisible information, the so-called blind spots. These areas are a significant problem, since artificial intelligence cannot recognize a complete object in them due to the lack of information. That is why when processing point clouds, an experienced specialist is required who can competently process the data manually and supplement it if necessary.
Point clouds can be colored or black and white. According to Alexander, the second option is enough for his work - it contains enough information about the geometry and dimensions of the object needed to build a model. Colored point clouds are also in demand, but less so, since they take much longer and are more expensive to create.