Updating a series of tiles

update_tiles.js

 /**
  * scale = 128
  * i_limit = c.5600
  * j_limit = c.11000
  */
            for (var i = 0; i < i_limit; i += scale)
                for (var j = 0; j < j_limit; j += scale) {
                  //  if (i > i_limit) continue;
                 //   if (j > j_limit) continue;
                    var heights = _chunk(image_data, i, i + scale, j, j + scale);
                      // _chunk produces a 128 x 128 set of ints (nested arrays, 128 128-value arrays
                    var query = {min_image_i: i, min_image_j: j, image: image._id};
                    var set_heights = {"$set": {heights: heights}};
                    mit_model.update(query, _stub, set_heights);
// note my model's update profile is slightly rearranged - update(filter, callback, document)
                }
            callback();