curvature.analysisRun.computeCurvatureFit

Description

Removes consecutive duplicate points, optionally resamples a traced path at equal arc-length intervals, obtains an algebraic Kasa circle estimate, and minimizes radial squared error with base-MATLAB fminsearch. The result includes pixel-space values and, when calibration is valid, physical radius, curvature, residuals, RMSE, and traced length. No GUI or file is required.

Inputs

xPix

Numeric x-coordinate vector in image pixels (image columns). At least three unique consecutive point pairs must remain.

yPix

Numeric y-coordinate vector in image pixels (image rows), with the same number of elements as xPix.

calibration

Scale structure accepted by curvature.analysisRun.normalizeScaleCalibration. Important fields are referencePixels, referenceLength, unit, pixelsPerUnit, isCalibrated, and referenceLine. Empty or omitted input selects uncalibrated pixels.

doDensify

Logical-like scalar controlling equal-arc-length resampling. Default: true.

denseN

Number of resampled fitting points, rounded to an integer with a minimum of three. Default: 300.

fitPathX

Optional displayed-path x-coordinate vector.

fitPathY

Optional displayed-path y-coordinate vector. When fitPathX and fitPathY have equal length and at least three unique points, this path supplies curve length and, when doDensify is true, the circle fit. Otherwise the anchor vectors supply both calculations.

Calculations

R_px is the fitted radius and kappa_per_px = 1/R_px. rmse_px is the root mean square radial residual of the points used by the optimizer. When calibration.isCalibrated is true, displayed lengths are divided by pixelsPerUnit and displayed curvature is the reciprocal physical radius. residuals_show always corresponds to the original unique anchor points.

Outputs

fit

Scalar structure describing the successful fit.

Fit Fields

ok, message - true and empty text after a successful calculation. xc_px, yc_px, R_px - Circle center and radius in pixels. kappa_per_px, rmse_px - Pixel curvature and radial RMSE. R_show, kappa_show, rmse_show - Values in unitLen/unitK when calibrated, otherwise the corresponding pixel values. unitLen, unitK - Length and curvature units, for example "um" and "1/um", or "px" and "1/px" without calibration.

residuals_show

Anchor-point radial residual column vector in unitLen. xPix, yPix - Unique anchor coordinates used for reported residuals. xFit, yFit - Points passed to the circle optimizer. curveLength_px, curveLength_show, curveLengthUnit, curvePointCount - Polyline length result for the accepted fit path. referencePx, referenceLength, scaleUnit, px_per_unit,

usePhysicalScale

Effective scale metadata.

Errors

labkit_CurvatureMeasurement_app:NotEnoughPoints

Fewer than three unique anchor points remain.

labkit_CurvatureMeasurement_app:InvalidFit

Optimization returns a nonfinite or nonpositive radius.

Example

theta = (0:11).' * (2*pi/12);
x = 30 + 10*cos(theta);
y = 40 + 10*sin(theta);
fit = curvature.analysisRun.computeCurvatureFit(x, y, [], false);
assert(fit.ok && abs(fit.R_px - 10) < 1e-3)