Description

This PR enriches the SfM reconstruction report (Generate_SfM_Report in sfm_report.cpp) with comprehensive statistics and SVG visualizations to provide deeper insights into 3D reconstruction quality and ease comparisons across different feature detectors/matchers.

Key Enhancements

1. Track Length Distribution & Statistics:
   • Fix truncation bug: Previously, the mean track length was cast to IndexT (e.g., 2.89 became 2), hiding structural differences between methods. It is now computed and displayed as a floating-point value (double).
   • Added exhaustive distribution metrics: min, max, mean, median, standard deviation, and percentiles (P25, P50, P75, P90, P95, P99).
   • Added a Categorized Breakdown table (2 views minimal, 3 views short, 4–5 views medium, 6–9 views good, 10+ views robust) with track counts, % tracks, observation counts, and % observations.
   • Added a Detailed Occurrence table length-by-length (with individual % and cumulative %).
   • Generated and embedded a dedicated tracks_histogram.svg.
2. Triangulation Conditioning & Parallax Angles ($\theta_{\max}$):
   • Evaluates triangulation robustness by computing the maximum ray angle between observing camera pairs for each 3D landmark:
     $$\theta_{\max} = \max_{i < j} \arccos\left(\frac{(\mathbf{X} - \mathbf{C}_i) \cdot (\mathbf{X} - \mathbf{C}_j)}{|\mathbf{X} - \mathbf{C}_i|_2 |\mathbf{X} - \mathbf{C}_j|_2}\right)$$
   • Reports angular distribution summary (min, mean, median, percentiles, max) and distribution bands ($< 2^\circ$ ill-conditioned, $[2^\circ, 5^\circ)$, $[5^\circ, 10^\circ)$, $[10^\circ, 20^\circ)$, $\ge 20^\circ$ wide baseline).
   • Generated and embedded parallax_angles_histogram.svg.
3. Camera Covisibility Graph:
   • Computes connected camera pairs (sharing $\ge 1$ point and $\ge 30$ points).
   • Reports shared landmark statistics per pair (min / median / mean / max).
4. 2D Reprojection Error (Vector Norm):
   • Added 2D Euclidean norm error metrics ($e = |\mathbf{r}|_2$): 2D RMSE, mean, median, P25..P99, max, and error distribution bands ($[0, 0.5]$ px, $(0.5, 1.0]$ px, $(1.0, 2.0]$ px, $> 2.0$ px).
   • 100% Backward compatible: The historical 1D coordinate RMSE and per-view residual table are preserved.
5. Terminal Summary Logging:
   • Automatically logs a clean, structured summary in the console (OPENMVG_LOG_INFO) upon report generation.
6. Unit Tests:
   • Added a dedicated unit test executable openMVG_test_sfm_report testing:
     • Empty scene handling (clean failure without file creation).
     • Synthetic multi-view scene (verifies report generation, HTML sections, and SVG outputs).