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user_manual:scan_quality_feedback

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Scan Quality Feedback

This page describes how to interpret the scan quality evaluation at the bottom of the “Scan Result” window (since DAVID Version 2.3).

Each value is shown on differently colored background as a simple evaluation of the respective scan condition:

  • green: very good,
  • yellow: acceptable/good,
  • red: poor.

What do these values mean?

Hold your mouse over one of the values to get a short description:

  • a: Intersection angle [°] between laser light plane and camera view direction (should be around between 30° and 60°)
  • w: Average laser line width (per image column) [pixel]; should be as small as possible
  • b: Average overall image brightness; should be as low as possible
  • l: Length [pixel] of the laser line on the left background panel; should not be too short
  • r: Length [pixel] of the laser line on the right background panel; should not be too short
  • p: “Plane quality”, precision of the calculated pose of the laser light plane; p should be as low as possible.

Is not measured and displayed, but important anyway: Please move the laser line slowly over the object surface, without shaking.

How can I improve the conditions?

  • a: Hold your laser at a different height above/below the camera.
  • w: Improve camera focus and/or laser focus. Decrease exposure / image brightness - the laser line does not need to be bright white. It is more important to have a thin, sharp laser line on the object than on the background panels.
  • b: Decrease exposure / image brightness and, more important, ensure constant environment brightness. After clicking “Start”, the whole camera image should not change (except for the laser line). Make sure all your camera's automatic image adjustments are switched OFF.
  • l, r: In the left and right side of the camera image, starting at the left and right image border, DAVID needs to see the laser line on the background panels. Place your object as far into the corner as possible, and if necessary, increase the distance of the camera.
  • p: If you don't get a value below 1.0 here, make sure that your background panels have an exact 90° angle, and make sure your camera calibration is still accurate.

What happens if these values are not optimal?

  • a: Low scan precision/strong surface noise; noise in shape of horizontal stripes on the scanned surface
  • w: Low scan precision/details
  • b: Noisy scan, stray outlier scan points; problems detecting the laser line
  • l, r: Low scan precision; noise in shape of horizontal stripes on the scanned surface
  • p: Low scan precision; distortion of scanned data; data aquired from different laser position won't fit to each other

Green vectors of Calibration

When you calibrate your camera, and this step is correctly accomplished, some green lines appear all over the camera view: one green vector for every marker (rings/dots) that is correctly founded and calibrated (successfully Calibration). These voctors are visual rapresentation of the distance between the center of your ring/dot and the estimated one. In other words, every lines shows how big is the distance between the real calibrated point (in your scene) and the hypotetic marker that David expect (math estimation). The orientation of the vectors shows the position of the real marker's center and of the estimated one (the centers are the two points of the green segment).

The value of the deviation between real and hypotetic positions of the markers is multiplied x10. So, don't worry if you get green lines after every calibration: the important thing is to reduce, as possible, their lenght. To avoid big green vectors you need to have a very precise calibration angle and flat and planar panels. Take in mind that the prospective aberration/deformation of the camera optics play a role, in this case. To reduce the problem, avoid the very wide lenses, especially if they are cheap and plastic lenses.

user_manual/scan_quality_feedback.txt · Last modified: 2014/06/06 18:38 (external edit)