95％。A new tractor navigation line detection arithmetic, named rotation and projection arithmetic, was put forward. At first, the image ROI rotates a series of given angles and for each rotation the ROI’s column average values were computed. And then the column average values and the enumeration angles compose the rotation and projection matrix R. Through all row vectors difference operation in R the difference rotation and projection matrix Rd was attained by whose extremum values the image navigation line parameters can be found out (including heading angle and lateral position). Finally the world coordinate guidance line parameters were attained by those parameters. By using the same principle the field end line can also be detected. In order to make the arithmetic more efficient, there are four measures to be used: setting appropriate ROI, utilizing linear reducing, starting as rough-divisiory rotation angle and then elaborate-divisiory rotation angle, using the former frame information. Those measures make one frame processing time in 6.2ms or so. Using various mature wheat images testing indicates that the precision rate of recognizing navigation line is up to 95%. 