Method and apparatus for image registration

A method of registering surface measurements taken from an object to reference data representing specifications for said object, the method implemented on a programmable computer, the method comprising the steps of:

• measuring said surface of said object to obtain a plurality of surface data points qi;
• analyzing said reference data to determine a plurality of patches Pi each comprising one or more sections having curvature corresponding to local minima;
• determining a surface normal vector ni, and center location pi for each of said patches Pi;
• projecting a line from pi, along ni to intersect a surface data point qi;
• and
• calculating a sum of distances d(P,P′) between points pi and qi for a plurality i of said low curvature surface patches to a obtain pose error.

A method of comparing a theoretical N dimensional model surface to N dimensional measured data surface points of an object comprising the steps of:

• a) acquiring said N dimensional model;
• b) analyzing said model to determine a plurality of low curvature surface patches Pi, each Pi having a curvature less than a predetermined curvature threshold;
• c) determining a surface normal vector ni, and center location pi for each of said low curvature surface patches Pi;
• d) projecting a line from pi to intersect with location qi on the surface data;
• e) determining a pose error, being a sum of distances d(P,P′) between locations pi and qi for a plurality of patches i;
• f) minimizing the sum of distances d(P,P′) to result in the pose error;
• g) adjusting the pose of the N dimensional model relative to the N-dimensional data to according to the calculated pose error as a rough pose;
• h) calculating a statistical distribution of a plurality of data surface points;
• i) determining deviation from the calculated statistical distribution of a plurality of data surface;
• j) comparing the each of the plurality of data surface points to the statistical distribution;
• k) attributing a weight to each of the plurality of surface data points based upon the comparison to the statistical distribution, being between 1 and 0, with the weight going toward 0 as the distance from the center of the statistical distribution increases.
• l) multiplying each range data point by its weighting to result in weighted surface data;
• m) repeating steps (b) through (g) above to solve for fine pose using the weighted measured data in place of the original measured data;
• n) adjusting the rough pose of the N dimensional model relative to the N-dimensional surface data to according to the calculated pose error from the weighted measured data.

A system for adjusting pose registration between a theoretical N dimensional model surface to N dimensional measured data surface represented by the model comprising:

• a) a patch determination device for determining a plurality of patches Pi each having less than a predetermined surface curvature;
• b) a patch center device functionally coupled to the patch determination device for calculating a center point pi for each of the plurality of low curvature surface patches;
• c) normal vector calculation device functionally coupled to the patch determination device and the patch center device for determining a vector ni normal to each patch Pi at its center point pi;
• d) a geometric determination device functionally coupled to the patch center, and normal vector calculation devices, and the surface data source , which extends the normal vector ni until it intersects with surface data at location qi;
• e) a distance minimization device functionally coupled to the patch center, normal vector calculation and geometric calculation devices for determination of rotation intermediates (ω, t″);
• f) rotation conversion device coupled to the distance minimization device for receiving rotation intermediates (W,t″) and for converting them into pose error (R,t);
• and
• g) an offset device coupled to the rotation conversion device, the surface data source and the model source, for receiving pose error (R,t) and adjusting the surface data and model pose according to the pose error (R,t).