Method for determining edge positions

• US 5,802,206 A
• Filed: 01/16/1996
• Issued: 09/01/1998
• Est. Priority Date: 01/13/1995
• Status: Expired due to Term

• Current Assignee: Trimble Jena GmbH (Trimble Inc.)
• Original Assignee: CARL Zeiss JENA GmbH (Carl-Zeiss-Stiftung)
• Inventors: Marold, Thomas
• Primary Examiner(s): Couso, Yon J.
• Assistant Examiner(s): Nguyen, Ha Tran
• Application Number:
  US08/585,666
• Time in Patent Office: 959 Days
• Field of Search: 382/199, 382/205, 382/291, 382/278, 235/462, 235/463
• US Class Current: 382/199
• CPC Class Codes: G01B 11/024 by means of diode-array scanning
• CPC Class Codes: G01C 15/06 Surveyors' staffs; Movable markers
• CPC Class Codes: G01D 5/342 the sensed object being the obturating part

Abstract

A method is provided for determining edge positions by evaluating digitized electrical signals which are obtained when scanning at least one light-dark structure by means of photoreceivers. The method is characterized in that the regions of four adjacent photoreceivers (i; i+1; i+2; i+3), in the middle of which is located an edge to be determined, are first determined from the signals Y_i, in that the type of edge, light edge, dark edge or dark-light edge or white-black transition or black-white transition is then determined from the signals Y_i, in that a value Mi is formed from the signals of the first two photoreceivers (i; i+1) in such a way that Mi is the extreme of Y_i and Y_i+1 to be expected for the determined type of edge, in that a value Ma is formed from the signals of the two other photoreceivers (i+2; i+3) in such a way that Ma is the extreme of Y_i+2 and Y_i+3 to be expected for the determined type of edge, and in that the position x of the edge to be determined is then determined with reference to the dividing edge of the two photoreceivers i+1; i+2 in units of the photoreceiver dimensions according to the following equation: ##EQU1##

Claims

1. In a method for determining edge positions by evaluating digitized electrical signals which are obtained when scanning at least one light-dark structure by photoreceivers, the improvement comprising the steps of:

determining an edge which is located in the middle of the regions of four adjacent photoreceivers (i;

i+1;

i+2;

i+3), which provide lightness signals Y_i, Y_i+1, Y_i+2, and Y_i+3, first determining said regions from the signals Y_i ;

determining the type of edge, light edge, dark edge or dark-light edge or white-black transition or black-white transition from the signals Y_i ;

forming a value Mi from the lightness signals of the first two photoreceivers (i;

i+1) so that Mi is an extreme of Y_i and Y_i+1 to be expected for the determined type of edge;

forming a value Ma from the signals of the two other photoreceivers (i+2;

i+3) so that Ma is an extreme of Y_i+2 and Y_i+3 to be expected for the determined type of edge; and

determining the position x of the edge to be determined with reference to a dividing edge of the two photoreceivers i+1;

i+2 in units of the photoreceiver dimensions according to the following equation;

##EQU3##

2. The method according to claim 1, wherein the regions of four adjacent photoreceivers, in the middle of which is located an edge to be determined, are given by a local extreme of a cross-correlation function (CCF)

3. The method according to claim 2, wherein an edge of the same kind as the comparison edge is associated with a local maximum of the CCF and an edge of the opposite type with respect to the comparison edge is associated with a local minimum of the CCF.

4. The method according to claim 3, wherein a maximum is associated with a black-white transition and a minimum is associated with a white-black transition for a photometrically negative image content and a CCF=Y_i +Y_i+1 -Y_i+2 -Y_i+3.

5. The method according to claim 3, wherein a maximum is associated with a white-black transition and a minimum is associated with a black-white transition for a photometrically positive image content and a CCF=Y_i +Y_i+1 -Y_i+2 -Y_i+3.

6. The method according to claim 1, including the step of using CCD elements as the photoreceivers (i;

i+1;

i+2;

i+3).