The actual meaning of neighbor definition?

[jiayily]

Hello, I 'm very confused about the definition of neighbors.

TRAVEL/include/travel/tgs.hpp

Lines 739 to 794 in ea9520a

	switch (s_i) {
	case 0:
	tmp_neighbors.push_back({r_i+1, c_i+1, 2});
	tmp_neighbors.push_back({r_i+1, c_i+1, 3});
	tmp_neighbors.push_back({r_i+1, c_i , 1});
	tmp_neighbors.push_back({r_i+1, c_i , 2});
	tmp_neighbors.push_back({r_i+1, c_i , 3});
	tmp_neighbors.push_back({r_i+1, c_i-1, 1});
	tmp_neighbors.push_back({r_i+1, c_i-1, 2});
	tmp_neighbors.push_back({r_i , c_i+1, 0});
	tmp_neighbors.push_back({r_i , c_i+1, 3});
	tmp_neighbors.push_back({r_i , c_i-1, 0});
	tmp_neighbors.push_back({r_i , c_i-1, 1});
	break;
	case 1:
	tmp_neighbors.push_back({r_i+1, c_i+1, 2});
	tmp_neighbors.push_back({r_i+1, c_i+1, 3});
	tmp_neighbors.push_back({r_i+1, c_i , 1});
	tmp_neighbors.push_back({r_i+1, c_i , 2});
	tmp_neighbors.push_back({r_i , c_i+1, 0});
	tmp_neighbors.push_back({r_i , c_i+1, 2});
	tmp_neighbors.push_back({r_i , c_i+1, 3});
	tmp_neighbors.push_back({r_i-1, c_i+1, 0});
	tmp_neighbors.push_back({r_i-1, c_i+1, 3});
	tmp_neighbors.push_back({r_i-1, c_i+1, 0});
	tmp_neighbors.push_back({r_i-1, c_i , 1});
	break;
	case 2:
	tmp_neighbors.push_back({r_i , c_i+1, 2});
	tmp_neighbors.push_back({r_i , c_i+1, 3});
	tmp_neighbors.push_back({r_i , c_i-1, 1});
	tmp_neighbors.push_back({r_i , c_i-1, 2});
	tmp_neighbors.push_back({r_i-1, c_i+1, 0});
	tmp_neighbors.push_back({r_i-1, c_i+1, 3});
	tmp_neighbors.push_back({r_i-1, c_i , 0});
	tmp_neighbors.push_back({r_i-1, c_i , 1});
	tmp_neighbors.push_back({r_i-1, c_i , 3});
	tmp_neighbors.push_back({r_i-1, c_i-1, 0});
	tmp_neighbors.push_back({r_i-1, c_i-1, 1});
	break;
	case 3:
	tmp_neighbors.push_back({r_i+1, c_i , 2});
	tmp_neighbors.push_back({r_i+1, c_i , 3});
	tmp_neighbors.push_back({r_i+1, c_i-1, 1});
	tmp_neighbors.push_back({r_i+1, c_i-1, 2});
	tmp_neighbors.push_back({r_i , c_i-1, 0});
	tmp_neighbors.push_back({r_i , c_i-1, 1});
	tmp_neighbors.push_back({r_i , c_i-1, 2});
	tmp_neighbors.push_back({r_i-1, c_i , 0});
	tmp_neighbors.push_back({r_i-1, c_i , 3});
	tmp_neighbors.push_back({r_i-1, c_i-1, 0});
	tmp_neighbors.push_back({r_i-1, c_i-1, 1});
	break;
	default:
	break;
	}

What' the actual meaning of above neighbor selection? Why not chose from the (4*8+3 = 35) triangle nodes of its 8-neighborhood?