Tune the pre-tracking stage

src/trackers/image-tracker/settings.ts

 /** Minimum acceptable number of matched keypoints when in a pre-tracking state */
 export const PRE_TRACK_MIN_MATCHES = 4;
 
-/** Maximum number of iterations in Pre-tracking B */
-export const PRE_TRACK_MAX_ITERATIONS = 3;
+/** Used to identify the best maches */
+export const PRE_TRACK_MATCH_RATIO = 0.6; // usually a value in [0.6, 0.8] - low values => strict tracking
 
 /** Reprojection error, in NIS pixels, used when pre-tracking */
 export const PRE_TRACK_RANSAC_REPROJECTIONERROR_NIS = (NIS_SIZE * 0.0125 * 0.5) | 0;
 /** Reprojection error, in NDC, used when pre-tracking */
 export const PRE_TRACK_RANSAC_REPROJECTIONERROR_NDC = PRE_TRACK_RANSAC_REPROJECTIONERROR_NIS / (NIS_SIZE / 2);
 
+/** Interpolation filter: interpolation factor */
+export const PRE_TRACK_FILTER_ALPHA = 0.8;
+
+/** Interpolation filter: correction strength for noisy corners */
+export const PRE_TRACK_FILTER_BETA = 1;
+
+/** Maximum number of iterations in Pre-tracking B */
+export const PRE_TRACK_MAX_ITERATIONS = 6; // the less the interpolation factor, the more iterations are needed
+
 /** Minimum acceptable number of matched keypoints when in the tracking state */
 export const TRACK_MIN_MATCHES = 4;//10; //20;
 
 export const TRACK_FILTER_TAU = 0.2;
 
 /** Interpolation filter: rotational factor */
-export const TRACK_FILTER_OMEGA = 0.05; // keep it close to zero
+export const TRACK_FILTER_OMEGA = 0.05; // keep it zero or close to zero

src/trackers/image-tracker/states/pre-tracking-b.ts

     TRACK_HARRIS_QUALITY, TRACK_DETECTOR_CAPACITY, TRACK_MAX_KEYPOINTS,
     SUBPIXEL_GAUSSIAN_KSIZE, SUBPIXEL_GAUSSIAN_SIGMA,
     PRE_TRACK_MIN_MATCHES, PRE_TRACK_MAX_ITERATIONS,
-    TRACK_MATCH_RATIO, PRE_TRACK_RANSAC_REPROJECTIONERROR_NDC,
+    PRE_TRACK_MATCH_RATIO, PRE_TRACK_RANSAC_REPROJECTIONERROR_NDC,
+    PRE_TRACK_FILTER_ALPHA, PRE_TRACK_FILTER_BETA,
     NIGHTVISION_QUALITY,
     SUBPIXEL_METHOD,
 } from '../settings';
             sourceBuffer.frozen = true;
 
             // refine the homography
-            return this._homography.setTo(warp.times(this._homography));
+            //return this._homography.setTo(warp.times(this._homography));
+
+            // apply filter
+            return ImageTrackerUtils.interpolateHomographies(
+                this._homography,
+                Speedy.Matrix(warp.times(this._homography)),
+                PRE_TRACK_FILTER_ALPHA,
+                PRE_TRACK_FILTER_BETA
+            );
+
+        })
+        .then(filteredHomography => {
+
+            // test: count the number of iterations needed
+            // for stabilization with this setup of the filter
+            //console.log(this._iterations);
+
+            // refine the homography
+            return this._homography.setTo(filteredHomography);
 
         })
         .then(_ => ({
         return ImageTrackerUtils.findPerspectiveWarpNDC(points, {
             method: 'pransac',
             reprojectionError: PRE_TRACK_RANSAC_REPROJECTIONERROR_NDC,
-            numberOfHypotheses: 512*8, // we want a really good homography
+            numberOfHypotheses: 512,
             bundleSize: 128,
             mask: undefined // score is not needed
         }).then(([ warp, score ]) => {
 
                 // the best match should be "much better" than the second best match,
                 // which means that they are "distinct enough"
-                if(d1 <= TRACK_MATCH_RATIO * d2) {
+                if(d1 <= PRE_TRACK_MATCH_RATIO * d2) {
                     const srcKeypoint = srcKeypoints[destKeypoint.matches[0].index];
                     pairs.push([srcKeypoint, destKeypoint]);
                 }