change threshold for sfm validity

Author: Fabien Servant

src/aliceVision/sfm/pipeline/sequential/ReconstructionEngine_sequentialSfM.cpp

@@ -227,7 +227,16 @@ bool ReconstructionEngine_sequentialSfM::process()
 
     exportStatistics(elapsedTime);
 
-    return !_sfmData.getPoses().empty();
+    const size_t nbviews = _sfmData.getViews().size();
+    const size_t nbposes = _sfmData.getPoses().size();
+
+    size_t minPoses = 1;
+    if (nbviews > _params.smallDatasetLimit)
+    {
+        minPoses = 3;
+    }
+
+    return (nbposes >= minPoses);
 }
 
 void ReconstructionEngine_sequentialSfM::initializePyramidScoring()

src/aliceVision/sfm/pipeline/sequential/ReconstructionEngine_sequentialSfM.hpp

@@ -47,6 +47,9 @@ class ReconstructionEngine_sequentialSfM : public ReconstructionEngine
         bool useLocalBundleAdjustment = false;
         int localBundelAdjustementGraphDistanceLimit = 1;
 
+        //Number of views under which a dataset is considered small
+        size_t smallDatasetLimit = 5;
+
         /// Dump current status of the scene every 3 resections
         bool logIntermediateSteps = false;