SPECIFICATIONS
3D scanning by laser scanner

 

I. General principles
As part of our future collaboration, we will define the common language elements on the different terms used to describe 3D scanning by laser scanner.


 Three-dimensional scanner: A 3D scanner generally measures the positioning of a sampling of points in a coordinate system - a cloud of points - on the surface of a subject and then extrapolates the shape from their distribution: this process is called a 3D reconstruction. If the color of each point is analyzed, then that of the surface can also be reconstructed.
Analogies exist between a camera and a 3D scanner. Both have a field of vision and cannot see what is hidden, both technologies being optical. If the first captures the colors of the surfaces in its field, the other measures its relative positioning in relation to a sample of points on the surfaces.
The image produced is based on a series of data composed of the coordinates positioning each of the sampled points with respect to the 3D scanner. If a spherical coordinate system is used and the scanner is the origin, each point can then be identified by coordinates (r, φ, θ). r represents the distance from the scanner to the point. φ and θ are the angles formed between the line going from the origin to the point analyzed in two planes passing through the origin, one horizontal and the other vertical. These spherical coordinates make it possible to locate each point in space in relation to the scanner, a preliminary work necessary for the digital modeling of the three-dimensional image of the object.
Generally, the data (coordinates of the points) collected with a single pass are not sufficient to fully model a subject. The work has to be done many times, hundreds of times, from different perspectives. All the data collected must be reinterpreted and located in a single coordinate system and grouped. The process, using the different measurements before being reinterpreted until modeling is known as 3D acquisition.


 Scanning or Digitization (S / N):
Scanning or digitization is the operation which makes it possible to acquire all the data by the three-dimensional scanner.
 Accuracy (P):
The precision defines the spacing in mm between 2 points of the scanning at a distance of 10m. It varies between 15mm to 1.5mm
 Quality (Q):
Quality defines the noise level of the scanning point, the higher it is the longer the scanning time, the better the resulting scanning point.
 Resolution (R):
The resolution defines the precision of the scanning, it varies between 1/1 and 1/10, knowing that the resolution 1/1 defines an accuracy of 1.5mm and that 1/10 defines an accuracy of 15mm.
 Angle (A):
The angle defines the horizontal rotation of the scanner, it can vary from 0 ° to 360 °, this angle is defined on site during the scanning and according to the purpose of the scanning.
 Color (C):
The color defines whether the scanning will be done in color or black and white, if a scanning is done in black and white, it can no longer be colored later. Either take photos or redo a color scan.
 Station (ST):
The station corresponds to a shot by the scanner.
 Acquisition (ACQ):
The acquisition is the action of digitizing the object and / or site with its close environment, during the acquisition all the parameters such as Resolution, Quality, Angle, Color are indicated, as well as the number of stations.
 Assembly:
The assembly is the so-called “Post-processing” action allowing all the scans carried out by the stations during the so-called “Acquisition” phase to be grouped in a single file, the file thus assembled is called “Point cloud”, this operation is carried out with dedicated software such as "SCENE", "POINTCAB" or "3DRESHAPER" that EVIDENCES 3D has.
Once the assembly is completed, it is possible to export the point cloud file in different formats, what is called a "Deliverable"
 Deliverable:
The deliverable is a file extracted from post-processing, it can be in the form of an image called “Ortho-photos” (TIFF), of an image capture (Jpeg, Png) or even in vector form (DXF, DWG).
 WebShare and WebShareCloud:
These terms include 2 ways to consult the scanning that was carried out via an internet browser in a 360 ° visit mode with taking dimensions, information, photos and also to exchange information in collaboration with people allowed.
The WEBSHARE application works only on PC in 32 or 64 bit mode, it is a self-executing application supplied on a USB key.
The WEBSHARECLOUD application can be used via our internet platform by a subscription (weekly, monthly, quarterly or annually), it is a secure solution in the "CLOUD" for storing and sharing digital data on the internet. Digital data, like 3D documentation, must be available for several project partners. This solution allows a virtual visit, to take dimensions, shots, annotations, add content (images, text documents, video, etc.) in hyperlink. Accessible 24/7 on all fixed or mobile supports (computer, tablet, smartphone).

II. DETAILS LEVEL
The customer must define the purpose of the use of scanning, this purpose will allow us to choose the level of details during the acquisition of the object and / or its close environment.
Evidences 3D defines 4 main levels of details, they can be adapted if necessary if the client does not find them relevant for their use of the point cloud.
These levels of details are classified ND1 to ND4 representing basic precision for level ND1, the purpose of which is to be used for 2D plans and sections without further information of color, shape and volume and the level ND4, the purpose of which is to serve for details. architectural to be reproduced or saved for purposes of expertise, controls or educational, archeology requiring extreme precision and rendering of colors and textures.

 

Details levels:

 

ND-1
D (distance) 10m
R (resolution) 1/10
Q (Quality) x4
P (Accuracy) 15 mm
C (Color) Yes
A (Angle) 22 ° 5 45 ° 90 ° 180 ° 360 °
T (Time) 1'22 1'42 2'25 3'51 5'27

 

ND-2
D (distance) 10m
R (resolution) 1/4
Q (Quality) x4
P (Precision) 6 mm
C (Color) Yes
A (Angle) 22 ° 5 45 ° 90 ° 180 ° 360 °
T (Time) 2'32 2'50 5'00 7'51 10'00

   

ND-3
D (distance) 10m
R (resolution) 1/2
Q (Quality) x4
P (Precision) 3 mm
C (Color) Yes
A (Angle) 22 ° 5 45 ° 90 ° 180 ° 360 °
T (Time) 4'48 8'35 16'10 31'20 32'57

   

ND-4
D (distance) 10m
R (resolution) 1/1
Q (Quality) x4
P (Precision) 1.5 mm
C (Color) Yes
A (Angle) 22 ° 5 45 ° 90 ° 180 ° 360 °
T (Time) 15'32 30'03 59'07 1h57 1h58

III. SCANNING STATIONS
Evidences 3D digitizes a work or a site, using a terrestrial laser scanner.
The terrestrial laser scanner digitizes everything it sees, when there are masks, obstacles or any screen that does not allow scanning in its entirety, it is necessary to carry out several scanning stations.
The terrestrial laser scanner used theoretically allows to digitize in a station with a radius of 130m and without obstacles an area of ​​53,093 m². Depending on the level of detail defined, we obtain a point spacing at 130m and a relative exposure time equivalent to:

ND1: P = 195 mm with an exposure time of 5'27
ND2: P = 78 mm with an exposure time of 10'00
ND3: P = 39 mm with an exposure time of 32'57
ND4: P = 19.5 mm with an exposure time of 1h58


The number of scanning stations is determined according to the criteria of visibility, precision and purpose.
at. DEFINITION OF THE NUMBER OF SCANNING STATIONS
i. Indoors
In the case of indoor scanning, the number of scanning stations will be defined according to the complexity of the room and the purpose of the scanning.
In the following example we start on an assumption of a level of details ND1
100 m² space without partition
1 position is sufficient

 

100 m² building with 4 rooms, one with partition.
1 station per room without partition for rooms 1 to 3
Additional station in order to have the whole room, here 1 additional station for room 4
ii. Outdoors
To perform a facade scan, the number of stations is defined in this way regardless of the level of detail chosen.
1 station in each corner if the length of the facade is less than or equal to 10m
An intermediate station if the length of the facade is more than 10m and less than 15m, beyond count an intermediate station every 10m. Additional stations will be mandatory if the work to be scanned has concave or convex shapes.
When the work to be scanned at a height greater than 15m, intermediate stations must be provided in height every 10m with a tripod, carrycot or any other means that can be made available by the customer.
NOTE: in general as soon as there is an obstacle (wall, post, beam, cornice, etc ...), not allowing to scan the entire structure or site and if the purpose of the scanning requires it, it is necessary to multiply scanning stations.

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