Even if genlod can do an incremental build that doesn't imply it should.

native/src/api.cpp

@@ -1235,6 +1235,7 @@ public:
     std::tie(stats, histo) =
       InternalZGY::GenLodC(_accessor_rw, _meta_rw, _lodcompressor,
                            EnumMapper::mapDecimationTypeToLodAlgorithm(decimation),
+                           action == FinalizeAction::BuildIncremental,
                            progress, /*verbose=*/false).call();
 
     // If doing an incremental rebuild: The statistics collected by

native/src/impl/genlod.cpp

@@ -86,6 +86,7 @@ GenLodBase::GenLodBase(
     const std::vector<LodAlgorithm>& decimation,
     const std::shared_ptr<HistogramData>& histogram,
     double defaultstorage,
+    bool incremental,
     const std::function<bool(std::int64_t,std::int64_t)>& progress,
     bool verbose)
   : _nlods(nlods_in)
@@ -99,6 +100,7 @@ GenLodBase::GenLodBase(
       LodAlgorithm::LowPass, LodAlgorithm::WeightedAverage} : decimation)
   , _wa_histogram(histogram) // Might point to self._histo later.
   , _wa_defaultstorage(defaultstorage)
+  , _incremental(incremental)
   , _progress(progress)
   , _verbose(verbose)
 {
@@ -253,10 +255,11 @@ GenLodImpl::GenLodImpl(
     const std::vector<LodAlgorithm>& decimation,
     const std::shared_ptr<HistogramData>& histogram,
     double defaultstorage,
+    bool incremental,
     const std::function<bool(std::int64_t,std::int64_t)>& progress,
     bool verbose)
   : GenLodBase(size, bricksize, dtype, histogram_range, nlods_in, decimation,
-               histogram, defaultstorage, progress, verbose)
+               histogram, defaultstorage, incremental, progress, verbose)
   , _stats(std::make_shared<StatisticData>())
   , _histo(std::make_shared<HistogramData>(256, histogram_range[0], histogram_range[1]))
 {
@@ -329,16 +332,16 @@ GenLodImpl::_accumulateT(const std::shared_ptr<const DataBuffer>& data_in)
 /**
  * Keep a running tally of statistics and histogram.
  *
- * TODO-@@@-Low: Performance: When doing an incremental
- * build this data will be discarded so we might as well
- * not collect it in the first place.
- * Add a bool GenLodImpl::_incremental
+ * When doing an incremental build this data will be discarded
+ * so it might as well not be collected it in the first place.
  */
 void
 GenLodImpl::_accumulate(const std::shared_ptr<const DataBuffer>& data)
 {
   if (!data)
     return;
+  if (_incremental)
+    return;
   switch (data->datatype()) {
   case RawDataType::SignedInt8:    _accumulateT<std::int8_t>(data); break;
   case RawDataType::UnsignedInt8:  _accumulateT<std::uint8_t>(data); break;
@@ -399,6 +402,8 @@ GenLodImpl::_accumulate(const std::shared_ptr<const DataBuffer>& data)
  * impractical. At least make sure the histogram updfate is done early
  * enough and the decimation late enough that the chunk of data being
  * decimated has already been added to the histogram.
+ *
+ * TODO-@@@: if (_incremental) may want to reduce the block size.
  */
 std::shared_ptr<DataBuffer>
 GenLodImpl::_calculate(const std::array<std::int64_t,3>& readpos_in, std::int32_t readlod)
@@ -791,6 +796,7 @@ GenLodC::GenLodC(
     const std::shared_ptr<ZgyInternalMeta>& meta,
     const compressor_t& lodcompressor,
     const std::vector<LodAlgorithm>& decimation,
+    bool incremental,
     const std::function<bool(std::int64_t,std::int64_t)>& progress,
     bool verbose)
   : GenLodImpl(meta->ih().size(),
@@ -802,11 +808,17 @@ GenLodC::GenLodC(
                decimation,
                nullptr, // Will use computed histogram so far.
                meta->ih().defaultstorage(),
+               incremental,
                progress,
                verbose)
   , _accessor(accessor)
   , _lodcompressor(lodcompressor)
 {
+  // Doing a full build even when incremental changes have been tracked
+  // is ok; that is up to the application to choose. The inverse won't
+  // work and should have been tested for earlier.
+  if (incremental && accessor->trackedBricks().size() == 0)
+    throw OpenZGY::Errors::ZgyInternalError("GenLodC inconsistent parameters.");
   if (this->_verbose)
     std::cout << "@ GenLod is created."
               << " Written range   " << accessor->valueRangeWritten()
@@ -859,14 +871,11 @@ GenLodC::_willneed() const
   // rebuilds touch the data they ought to. Even though only the final
   // count is checked.
 
-  // TODO-@@@ A virtual method or a data member telling us when an
-  // incremental buid is in progress. If not, this entire code block
-  // can be skipped. Knowing about incremental builds might also suggest
-  // other changes. Such as reducing the block size in _calculate().
-
   // Subtract the bricks skipped because of incremental build.
   // If full build then _canread() returns false for all lod>0
   // and the code below, even without a short cut, would do nothing.
+  if (!_incremental)
+    return total;
 
   sz = this->_surveysize;
   std::array<std::int64_t,3> max = sz; // Limit imposed by survey size @ lod-1
@@ -933,8 +942,8 @@ GenLodC::_canread(
   if (lod == 0) {
     return true;     // Fullres always read from file.
   }
-  else if (this->_accessor->trackedBricks().size() == 0) {
-    return false;    // Not tracking dirty bits => no BuildIncremental.
+  else if (!_incremental) {
+    return false;    // Not tracking dirty bits, or caller wants full anyway.
   }
   else if ((this->_accessor->trackedBricksDirty(pos, size, lod) & 0x01) != 0) {
     return false;    // Something dirty somewhere in the input.

native/src/impl/genlod.h

@@ -66,6 +66,7 @@ protected:
   std::vector<LodAlgorithm> _decimation;
   std::shared_ptr<HistogramData> _wa_histogram;
   double _wa_defaultstorage;
+  bool _incremental;
   std::function<bool(std::int64_t,std::int64_t)> _progress;
   bool _verbose;
 
@@ -78,6 +79,7 @@ public:
              const std::vector<LodAlgorithm>& decimation,
              const std::shared_ptr<HistogramData>& histogram,
              double defaultvalue,
+             bool incremental,
              const std::function<bool(std::int64_t,std::int64_t)>& progress,
              bool verbose);
 protected:
@@ -116,6 +118,7 @@ public:
              const std::vector<LodAlgorithm>& decimation,
              const std::shared_ptr<HistogramData>& histogram,
              double defaultvalue,
+             bool incremental,
              const std::function<bool(std::int64_t,std::int64_t)>& progress,
              bool verbose);
   std::tuple<std::shared_ptr<StatisticData>, std::shared_ptr<HistogramData>>
@@ -157,6 +160,7 @@ public:
           const std::shared_ptr<ZgyInternalMeta>& meta,
           const compressor_t& lodcompressor,
           const std::vector<LodAlgorithm>& decimation,
+          bool incremental,
           const std::function<bool(std::int64_t,std::int64_t)>& progress,
           bool verbose);
 protected: