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grid_construction

  • construct a grid from a bounding box

  • label a collection of points by grid cells

  • input: - points csv file with required columns lat,lon # see example input files (structures_households.csv)

  • output: - csv file of grid locations - csv with grid cell id added for each point record

construct(x_min, y_min, x_max, y_max)

Creating grid

Source code in emod_api/demographics/service/grid_construction.py 
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def construct(x_min, y_min, x_max, y_max):
    '''
    Creating grid
    '''

    logging.info("Creating grid...")

    # create corners of rectangle to be transformed to a grid
    min_corner = Point((x_min, y_min))
    max_corner = Point((x_max, y_max))

    # get the centroid of the cell left-down from the grid min corner; that is the origin of the grid
    origin = geod.fwd(min_corner.x, min_corner.y, -135, cell_size / math.sqrt(2))
    origin = Point(origin[0], origin[1])

    # get the centroid of the cell right-up from the grid max corner; that is the final point of the grid
    final = geod.fwd(max_corner.x, max_corner.y, 45, cell_size / math.sqrt(2))
    final = Point(final[0], final[1])

    fwdax, backax, dx = geod.inv(origin.x, origin.y, final.x, origin.y)
    fwday, backay, dy = geod.inv(origin.x, origin.y, origin.x, final.y)

    # construct grid
    x = origin.x
    y = origin.y

    current_point = deepcopy(origin)
    grid_id_2_cell_id = {}

    idx = 0

    cell_id = 0
    grid_lons = []
    grid_lats = []

    gcids = []
    while x < final.x:
        y = origin.y
        idy = 0

        while y < final.y:
            y = geod.fwd(current_point.x, y, fwday, cell_size)[1]
            current_point = Point(x, y)

            grid_lats.append(current_point.y)
            grid_lons.append(current_point.x)

            grid_id = get_grid_cell_id(idx, idy)
            grid_id_2_cell_id[grid_id] = cell_id

            cell_id += 1
            gcids.append(cell_id)
            idy += 1

        x = geod.fwd(current_point.x, current_point.y, fwdax, cell_size)[0]
        current_point = Point(x, current_point.y)
        idx += 1

    grid = pd.DataFrame(data=grid_lats, index=np.arange(len(grid_lats)), columns=["lat"])
    grid["lon"] = grid_lons
    grid["gcid"] = gcids

    num_cells_x = len(set(grid_lons))
    num_cells_y = len(set(grid_lats))

    logging.info("Created grid of size")
    logging.info(str(num_cells_x) + "x" + str(num_cells_y))
    logging.info("Done.")

    return grid, grid_id_2_cell_id, origin, final