long resolveFlats_parallel(T& elev, SparsePartition<short>& inc, linearpart<float>& flowDir, std::vector<std::vector<node>>&islands, linearpart<float>& orelevDir) 
{
    long nx = flowDir.getnx();
    long ny = flowDir.getny();

    int rank;
    MPI_Comm_rank(MCW, &rank);

    int numFlatsChanged = 0, totalNumFlatsChanged = 0;

    flowTowardsLower(elev, flowDir, islands, inc);

    do {
        inc.share();
        numFlatsChanged = propagateBorderIncrements(flowDir, inc);

        MPI_Allreduce(&numFlatsChanged, &totalNumFlatsChanged, 1, MPI_INT, MPI_SUM, MCW);

        if (rank == 0) {
            printf("PRL: Lower gradient processed %d flats this iteration\n", totalNumFlatsChanged);
        }
    } while(totalNumFlatsChanged > 0);

    // Not all grid cells were resolved - pits remain
    // Remaining grid cells are unresolvable pits
    markPits(elev, flowDir, islands, inc);

    // Drain flats away from higher adjacent terrain
    SparsePartition<short> higherGradient(nx, ny, 0);
   
    flowFromHigher(elev, flowDir, islands, higherGradient);

    do {
        higherGradient.share();
        numFlatsChanged = propagateBorderIncrements(flowDir, higherGradient);

        MPI_Allreduce(&numFlatsChanged, &totalNumFlatsChanged, 1, MPI_INT, MPI_SUM, MCW);

        if (rank == 0) {
            printf("PRL: Higher gradient processed %d flats this iteration\n", totalNumFlatsChanged);
        }
    } while(totalNumFlatsChanged > 0);

    // High flow must be inverted before it is combined
    //
    // higherFlowMax has to be greater than all of the increments
    // higherFlowMax can be maximum value of the data type (e.g. 65535) but it will cause overflow problems if more than one iteration is needed
    short higherFlowMax = 0;

    for (auto& island : islands) {
        for (auto& flat : island) {
            short val = higherGradient.getData(flat.x, flat.y);
        
            if (val > higherFlowMax)
                higherFlowMax = val;
        }
    }

    // FIXME: Is this needed? would it affect directions at the border?
    short globalHigherFlowmax = 0;
    MPI_Allreduce(&higherFlowMax, &globalHigherFlowmax, 1, MPI_SHORT, MPI_MAX, MCW);

    for (auto& island : islands) {
        for (auto flat : island) {
            inc.addToData(flat.x, flat.y, globalHigherFlowmax - higherGradient.getData(flat.x, flat.y));
        }
    }

    inc.share();

    if (rank==0) {
        fprintf(stderr,"\nPRL: Setting directions\n");
        fflush(stderr);
    }

    uint64_t localFlatsRemaining = 0, globalFlatsRemaining = 0;
    double tempdxc, tempdyc;
    
    for (auto& island : islands) {
        for (node flat : island) {
            //setFlow2(flat.x, flat.y, flowDir, elev, inc);
            orelevDir.getdxdyc(flat.y, tempdxc, tempdyc);
            float DXX[3] = {0, tempdxc, tempdyc}; //tardemlib.cpp ln 1291
            float DD = sqrt(tempdxc * tempdxc + tempdyc * tempdyc); //tardemlib.cpp ln 1293

            SET2(flat.y, flat.x, DXX, DD, elev, inc, flowDir);
            
            if (flowDir.getData(flat.x, flat.y) == -1) {
                localFlatsRemaining++;
            }
        }
    }

    flowDir.share();
    MPI_Allreduce(&localFlatsRemaining, &globalFlatsRemaining, 1, MPI_UINT64_T, MPI_SUM, MCW);

    auto hasFlowDirection = [&](const node& n) { return flowDir.getData(n.x, n.y) != -1; };
    auto isEmpty = [&](const std::vector<node>& i) { return i.empty(); };
    
    // Remove flats which have flow direction set
    for (auto& island : islands) {
        island.erase(std::remove_if(island.begin(), island.end(), hasFlowDirection), island.end());
    }

    // Remove empty islands
    islands.erase(std::remove_if(islands.begin(), islands.end(), isEmpty), islands.end());

    return globalFlatsRemaining;
}
long resolveFlats(T& elevDEM, SparsePartition<short>& inc, linearpart<float>& flowDir, std::vector<std::vector<node>>&islands, linearpart<float>& orelevDir) 
{
    long nx = flowDir.getnx();
    long ny = flowDir.getny();

    int rank;
    MPI_Comm_rank(MCW, &rank);
    
    if (rank==0) {
        fprintf(stderr,"Resolving flats\n");
        fflush(stderr);
    }

    flowTowardsLower(elevDEM, flowDir, islands, inc);

    // Drain flats away from higher adjacent terrain
    SparsePartition<short> s(nx, ny, 0);
    
    flowFromHigher(elevDEM, flowDir, islands, s);

    // High flow must be inverted before it is combined
    //
    // higherFlowMax has to be greater than all of the increments
    // higherFlowMax can be maximum value of the data type but it will cause overflow problems if more than one iteration is needed
    short higherFlowMax = 0;

    for (auto& island : islands) {
        for (node flat : island) {    
            short val = s.getData(flat.x, flat.y);

            if (val > higherFlowMax)
                higherFlowMax = val;
        }
    }

    for (auto& island : islands) {
        for (auto flat : island) {
            inc.addToData(flat.x, flat.y, higherFlowMax - s.getData(flat.x, flat.y));
        }
    }

    if (rank==0) {
        fprintf(stderr,"Setting directions\n");
        fflush(stderr);
    }

    long flatsRemaining = 0;
    double tempdxc, tempdyc;
    for (auto& island : islands) {
        for (node flat : island) {
            //setFlow2(flat.x, flat.y, flowDir, elevDEM, inc);
            orelevDir.getdxdyc(flat.y, tempdxc, tempdyc);
            float DXX[3] = {0, tempdxc, tempdyc}; //tardemlib.cpp ln 1291
            float DD = sqrt(tempdxc * tempdxc + tempdyc * tempdyc); //tardemlib.cpp ln 1293

            SET2(flat.y, flat.x, DXX, DD, elevDEM, inc, flowDir);

            if (flowDir.getData(flat.x, flat.y) == -1) {
                flatsRemaining++;
            }
        }
    }

    auto hasFlowDirection = [&](const node& n) { return flowDir.getData(n.x, n.y) != -1; };
    auto isEmpty = [&](const std::vector<node>& i) { return i.empty(); };
    
    // Remove flats which have flow direction set
    for (auto& island : islands) {
        island.erase(std::remove_if(island.begin(), island.end(), hasFlowDirection), island.end());
    }

    // Remove empty islands
    islands.erase(std::remove_if(islands.begin(), islands.end(), isEmpty), islands.end());

    return flatsRemaining;
}