Precision Measurement with Target Marks

ELCOVISION 10 can use targets to measure single, precisely defined points with maximum accuracy. While automatically measured natural points have a measurement accuracy of about 0.2 to 0.5 pixels in the image, targets exceed this with an impressive 10 to 100-fold increase in accuracy on average. This precision in image measurement results in equally accurately determined object points, whereby point accuracies in the sub-millimetre range can be achieved almost effortlessly.

The typical measurement accuracies behave as follows for different target mark diameters D:

Diameter D Centre circle	Typical accuracy with which the centre of the target mark is measured	*Typical() point accuracy with a pixel size of 1mm on the object**
20 – 30 Pixel	75% better than 0.1 Pixel 38% better than 0.05 Pixel 10% better than 0.01 Pixel	75% better than 0.075mm 38% better than 0.037mm 10% better than 0.007mm
30 – 40 Pixel	82% better than 0.1 Pixel 48% better than 0.05 Pixel 20% better than 0.01 Pixel	82% better than 0.075mm 48% better than 0.037mm 20% better than 0.007mm
40 – 50 Pixel	88% better than 0.1 Pixel 55% better than 0.05 Pixel 25% better than 0.01 Pixel	88% better than 0.075mm 55% better than 0.037mm 25% better than 0.007mm

* When using a higher quality camera/lens combination and good image quality, 4-6 image measurements per target mark and good image capture configuration..

If the images are made in such a way that a target mark is visible in at least 8 images, the few "outliers" with poor image measurement accuracy can be identified and deleted using the global orientation, object point accuracies of better than 0.05mm are relatively easy to achieve.