(b) Cross-Correlation 
5. Conclusions 
G) The precisions of matching by cross-correlation 
(a) Least Squares Method for images in which no distortions exist are only 
marginally worse than for the least squares 
(1) Tests on the precision of image matching by the method. 
method of least squares indicate values as high 
as .02 pixel can be achieved with cross and (ii) The effects of distortions between the two 
circular features, but precisions will deteriorate images result in a rapid deterioration in the 
for quantization levels less than 5 bits. quality of matching by the cross-correlation 
method. 
(11) The extent of image blur has only a marginal 
effect on the precision of matching, with Ref 
precisions improving slightly as the blur eierences 
increases up to that described by a Gaussian 
spread function with a 26 width of 501m. Beyer, H. (1992) 'High Precision Real-time 
is 4 3 Photogrammetry’. PhD Dissertation Institute of 
(iii) The overall differences in the quality of Geodesy and Photogrammetry ETH-Zurich. 
matching for the cross and circle features are 
only marginal, with generally better results Foerstner W. (1982) 'On Geometric Precision of Digital 
being obtained for crosses than for circles. Correlation. Int. Arch. Photgram. & Rem Sens Vol. 
E ; 24-3 pp 176-189. 
(iv) Scale variations between the two images greater 
than 10% will lead to a significant decrease in Trinder J.C. (1989) "Precision of Digital Target Location'. 
the precision of image matching. Photogramm. Eng. and Rem. Sens Vol 55 pp 883-886. 
(v) There is good agreement between the Trinder J.C., T. Tjugiarto & B.E. Donnelly (1990). 'A 
previously published theoretical precisions and Digital Photogrammetry System for Close Range'. Aust. 
those obtained by simulation in this study. J. Geod. Photogram. & Surv No. 53 pp 1-13. 
  
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