Commit 79c105c4 authored by Andrey Filippov's avatar Andrey Filippov
Browse files

CLAUDE: undistortPxPy(): invert correction direction (getRDistByR) 



The RECTILINEAR nadir pass multiplied sampling coordinates by getRByRDist()
(distorted->ideal), but sampling positions must be moved to where the ideal
ray lands in the distorted image - the FORWARD distortion getRDistByR(),
same direction as GeometryCorrection.getImageCoordinates(). The old code
ADDED the common radial distortion to the output instead of removing it.

Evidence (graveyard ref 1763232420_274928, flat constant-disparity terrain
where translation flow must be uniform for a true pinhole image):
- plain NADIR-MERGED edge/center flow ratio 0.965 (expected 0.954 from the
  calibration polynomial: ~4.8 px barrel at the edge),
- old RECTILINEAR 0.952 - worse than uncorrected,
- COLMAP self-calibrated f=1003/k1=-0.385 on the old rectilinear stack.

Co-authored-by: default avatarClaude <claude@elphel.com>
parent af0e34b9

src/main/java/com/elphel/imagej/tileprocessor/OpticalFlow.java

+20 −10
Original line number Diff line number Diff line
@@ -11104,11 +11104,21 @@ java.lang.NullPointerException 
    }









    /**









     * Undistort pixel coordinates in a pXpYD tile array in-place.









     * Converts distorted sensor coordinates to rectilinear (pinhole) coordinates









     * using the scene's radial distortion calibration (getRByRDist).









     * With Boson 640, the correction is &lt;1 px but eliminates the systematic









     * bowl effect in COLMAP reconstructions that use a PINHOLE camera model.









     * Convert a pXpYD tile array (in-place) so that rendering it produces a









     * RECTILINEAR (pinhole) output image.









     *









     * The tile coordinates are SAMPLING positions in the common (radially









     * distorted) virtual-camera space.  For output pixel u (the tile grid) to









     * show the content of the ideal pinhole ray through u, it must sample the









     * distorted image where that ray actually lands: rD = R * (Rdist/R), i.e.









     * apply the FORWARD distortion getRDistByR() - same direction as









     * GeometryCorrection.getImageCoordinates() (world -> distorted pixel).









     *









     * (The previous version used getRByRDist() - the inverse - which ADDED the









     * common radial distortion to the output instead of removing it: measured









     * edge/center translation-flow ratio 0.952 vs 0.965 of the non-undistorted









     * stack, and COLMAP self-calibrated k1=-0.38 on supposedly pinhole images.)









     *









     * @param pXpYD  tile array: each non-null element is {pX, pY, disparity}









     * @param gc     GeometryCorrection providing distortion model and pixel geometry









     */










@@ -11122,11 +11132,11 @@ java.lang.NullPointerException







    		if (tile == null) continue;









    		double pXc = tile[0] - cx;









    		double pYc = tile[1] - cy;









    		double rD_mm = Math.sqrt(pXc * pXc + pYc * pYc) * mmPerPix;









    		if (rD_mm > 0) {









    			double rND2R = gc.getRByRDist(rD_mm / distRad, false);









    			tile[0] = pXc * rND2R + cx;









    			tile[1] = pYc * rND2R + cy;









    		double rND_mm = Math.sqrt(pXc * pXc + pYc * pYc) * mmPerPix;









    		if (rND_mm > 0) {









    			double rD2RND = gc.getRDistByR(rND_mm / distRad);









    			tile[0] = pXc * rD2RND + cx;









    			tile[1] = pYc * rD2RND + cy;









    		}









    	}









    }