Guehring, Jens 
  
Combining the above correction terms with the correction for affinity 
yields the corrected image point coordinates 
= X * dr, * dd, * da, 
X corr 
— y dr, * dd,. 
Mon 
Typical standard deviations are about 1/25 to 1/30 of the pixel size for the image point coordinates and about 5 4m for 
the object space coordinates within a measurement area of about 25x25cm^ which means a triangulation accuracy of 
1/50,000 . 
5 EXPERIMENTS 
This section reports some results and compares them with the ones of our previous setup. To make the numbers more 
comparable, we used only part of the image, located at the left edge of the sensor and seeing roughly the same area of 
the measurement volume as we used in our previous tests. This prevents the new system to benefit from the higher 
resolution of our new cameras 
Accuracy assessment was performed using a granite reference plane as calibration normal. This plane is certified to 
have an overall surface flatness of 7 microns. Since the surface is black, we covered it by a self-adhesive white foil to 
obtain a high signal modulation. The reference plane was positioned in front of the sensor both perpendicular to the 
optical axis and at different angles. The measurement area was about 20cm x 20cm. 
Images were taken for a single camera in combination with our calibrated projector. After a dense cloud of measured 
3D points is obtained, a plane is fit to the data and minimum, maximum and standard deviation of the points from the 
plane are determined. 
Table 1 shows the results of this step for our previous and current setup. From this table, we can see that our new 
approach has reduced standard deviations by half, compared to the previous method. It is also remarkable, that the 
maximum deviation was reduced by a factor of three. 
This translates to approximately 1:10,000 relative accuracy. 
  
  
  
  
  
  
Angle of Plane Previous System . . New System 
w.r.t Projector (Phase Shift Processing) (Line Shift Processing) 
(degrees) r.m.s. maximum r.m.s. maximum 
0 0.031 0.174 0.016 0.067 
-15 0.040 0.275 0.016 0.067 
10 0.041 0.268 0.019 0.073 
20 0.043 0.177 0.019 0.083 
  
  
  
  
  
  
  
Table 1. Deviations of measured 3D points from a fitted plane (in millimeters). 
One reason for the improved accuracy lies in our digital cameras that deliver pixel-synchronous information without 
any errors induced by a camera / framegrabber combination. The second reason is a modified camera model which 
gives better results especially for large radial distances. Third, we perform stricter consistency tests during data 
processing. Last, but not least, our new method gives more accurate results than phase shift processing. 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B5. Amsterdam 2000. 337