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**
10 – 15 Pixel	91% better than 0.10 Pixel 70% better than 0.05 Pixel 21% better than 0.02 Pixel 14% better than 0.01 Pixel	91% better than 0.075mm 70% better than 0.037mm 21% better than 0.014mm 14% better than 0.007mm
15 – 20 Pixel	94% better than 0.10 Pixel 80% better than 0.05 Pixel 31% better than 0.02 Pixel 20% better than 0.01 Pixel	95% better than 0.075mm 80% better than 0.037mm 31% better than 0.014mm 20% better than 0.007mm
20 – 30 Pixel	98% better than 0.10 Pixel 93% better than 0.05 Pixel 39% better than 0.02 Pixel 25% better than 0.01 Pixel	98% better than 0.075mm 93% better than 0.037mm 39% better than 0.014mm 25% better than 0.007mm
30 – 40 Pixel	99% better than 0.10 Pixel 94% better than 0.05 Pixel 42% better than 0.02 Pixel 28% better than 0.01 Pixel	99% better than 0.075mm 94% better than 0.037mm 42% better than 0.014mm 28% better than 0.007mm
40 – 50 Pixel	99% better than 0.10 Pixel 98% better than 0.05 Pixel 53% better than 0.02 Pixel 36% better than 0.01 Pixel	99% better than 0.075mm 98% better than 0.037mm 53% better than 0.014mm 36% better than 0.007mm
50 – 70 Pixel	99% better than 0.10 Pixel 97% better than 0.05 Pixel 65% better than 0.02 Pixel 46% better than 0.01 Pixel	99% better than 0.075mm 97% better than 0.037mm 65% better than 0.014mm 46% better than 0.007mm

*When using a higher quality camera/lens combination and good image quality, 4 or more 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.