7Andrzej Jaron’’ski.The National Geodetic Vertical Control Network of Poland. .
8Corrections Applied by the National Geodetic Survey to Precise Levelling Observations. NOAA Technical Memorandam NOS NGS34 . 1982
9CHEN G B, LIU J. Edge detection methods for Gray-R barcode grade rod [ M ]. ZHANG W. Edit. Software Engineering and Knowledge Engineering: Theory andPractice, Berlin : Springer,2012 : 287-292.