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Scanning Guide using Prescan and Positions Generator

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Overview

 
This article will cover a faster workflow for scanning objects using Prescan and Arago Control’s automatic position generator algorithm. Both Prescan and the Position Generator are included under the Arago Control perpetual license agreement. For license inquiries, please contact Rigsters ApS at [email protected].

Prescan

 

With Prescan, you can capture the intricate shape, curvature, and spatial position of your object before the actual scanning process begins. This innovative tool establishes a proxy 3D model, providing invaluable insights into optimal camera positions and ensuring seamless mesh reconstruction.

Open the feature by clicking on the “Prescan” button. Note that the feature is disabled if Arago is not connected and initialised.
 
 prescan panel

This will automatically instantiate in the scene the Prescan bounding box which we will describe later in this guide.

It is imperative that the USB connection is of type 3.x or higher to allow high speed data transfers between the Intel RealSense sensor and the PC.

Depth View and Live View

These two toggles enable the Intel RealSense sensor and starts streaming depth data into Arago Control. Depth View allows the user to display the data as a point cloud in the scene. The Live View showcases the flat RGB data, similar to the Camera Tethering Support live view.

Click on Depth View and enable the sensor.

intel sensor enabled 

Voxel resolution. If increased, the Prescan reconstruction algorithm will increase in data granularity. This is helpful if you are scanning smaller objects.

Scan mode.  There are three available modes and they can be described as follows:

  • Quick – 1 spin around the bounding box. In most cases this mode is sufficient to get a rough mesh.
  • Regular – 2 spins around the bounding box, one in the middle and one from the top.
  • Full – 3 spins around the bounding box, 2 the same as the Regular, plus one rotation from below.
 Use current position checkbox is used to specify that the prescan should be conducted from the current elevation in space of the Intel sensor.

Bounding Box

 

When the Prescan panel is opened, an opaque box is also created in the scene. The space enclosed by this box will determine the region processed during mesh reconstruction.
It is essential that your object is fully contained in the box. Re-adjust the size and the location of the box to fully contain the object. To accommodate the turntable spin, it is recommended to make this box larger than the object by 1/3.

bounding box adjusted

Reconstruction

Once ready, click “Start Prescan” and wait for the travel and reconstruction to finish. reconstructing 

In the lower right corner notice the reconstruction preview which shows you in realtime the results of the remeshing process.
In case the alignment process is failing, the process can be canceled at any time and restarted.

Reconstruction Post-processing

 
The result of the initial reconstruction can sometimes include outliers or regions that do not consist the object such as the turntable stand. To discard any unwanted area in the initial model the Reconstruction Post-processing step comes in hand with a cleaning, cropping, and fill-holes feature.
Alternatively, the mesh can also be saved if necessary for future scans, though the same functionality can be achieved by simply saving the project.
 
 reconstruction post processing

Click “Finish” once all desired post-processing corrections have been completed. Please note that this action cannot be reversed. Finish, will automatically fill-holes in the mesh and decimate the model for optimal computation times and open the Positions panel in the “Auto” mode which we describe in the next section.

Automatic Positions Generator

 
This innovative tool streamlines the process of position generation, eliminating the tedious manual labor traditionally associated with scanning setups. Whether you’re embarking on a journey to digitize real-world objects for 3D modeling, preservation, or analysis, the Automatic Positions Generator empowers you to effortlessly create optimal scanning configurations tailored to your specific needs.

automatic positions generator 

The algorithm is based on curvature analysis and ray-tracing and uses your the primary camera sensor size and the focal length to calculate the depth of field frustrum. 

You can utilize the feature iteratively until you attain an optimal set of positions that meet your requirements.

The settings available in this panel offer you a direct access to tweak the generative algorithm.

  •  Cut-off MIN angle°. Describes the minimum angle from top (zenith) where positions generation is allowed in the horizontal coordinate system. 
  • Cut-off MAX angle°. Describes the maximum angle from top (zenith) where positions generation is allowed in the horizontal coordinate system. 
  • Max surface ray angle°. Maximum angle deviated from the mesh normals for generating positions different orientations. A value of 1 would generate positions with an orientation asymptotically the same with selected normals on the mesh.
  • Tolerance radius. Describes the radius in milimiters of a sphere casted around each generated position where no other point is allowed. In effect, it spreads positions more evenly.
  • Max images. This count represents the maximum number of images permitted for the algorithm to generate. Most likely it will not generate this precise amount unless it under-generates.
  • Distance. Represents the distance between the spawn position and the surface of the proxy mesh.
  • Discard invalid. When activated, the generative algorithm will discard all invalid positions that Arago cannot reach at the end. It’s advisable to uncheck this option to gain a deeper understanding of the algorithm’s functionality.
The default settings should suffice to cover most common settings. Clicking “Generate” will delete all positions in the scene and create a new set based on the provided settings.

positions generated 

Start Travel

 
After generating the desired set of positions, navigate to “Start” and begin capturing by clicking “Play”. You can pause and resume the process at any time. Additionally, once the travel completes, you can restart the same sequence to capture another set of images using the same positions. This is particularly useful for capturing images under both polarized and non-polarized light.

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