CommandArea GetCommandArea(const CommandPacket *cp) {
        byte cmd = (cp->cmd & CMD_ID_MASK);
        switch (cmd) {
            case CMD_BUILD_RAIL_STATION: {
                Axis axis      = Extract<Axis, 4, 1>(cp->p1);
                byte numtracks = GB(cp->p1,  8, 8);
                byte plat_len  = GB(cp->p1, 16, 8);
                if (axis == AXIS_X)
                    return CommandArea(cp->tile, plat_len, numtracks);
                return CommandArea(cp->tile, numtracks, plat_len);
            }

            case CMD_BUILD_AIRPORT: {
                const AirportSpec *as = AirportSpec::Get(cp->p1);
                if (!as->IsAvailable()) return CommandArea(cp->tile);
                return CommandArea(cp->tile, as->size_x, as->size_y);
            }

            case CMD_PLANT_TREE:
                return CommandArea(cp->tile, cp->p2);

            case CMD_BUILD_RAILROAD_TRACK:
            case CMD_REMOVE_RAILROAD_TRACK:
            case CMD_BUILD_LONG_ROAD:
            case CMD_REMOVE_LONG_ROAD:
            case CMD_CLEAR_AREA:
            case CMD_BUILD_CANAL:
            case CMD_LEVEL_LAND:
            case CMD_BUILD_BRIDGE:
                // TODO diagonal areas
                return CommandArea(cp->tile, cp->p1);

            default:
                return CommandArea(cp->tile);
        }
        NOT_REACHED();
    }