/
terrain_gen.py
executable file
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/
terrain_gen.py
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#!/usr/bin/env python
'''
create ardupilot terrain database files
'''
import math, struct, os
import time, struct
import fastcrc
crc16 = fastcrc.crc16.xmodem
from MAVProxy.modules.mavproxy_map import srtm
# MAVLink sends 4x4 grids
TERRAIN_GRID_MAVLINK_SIZE = 4
# a 2k grid_block on disk contains 8x7 of the mavlink grids. Each
# grid block overlaps by one with its neighbour. This ensures that
# the altitude at any point can be calculated from a single grid
# block
TERRAIN_GRID_BLOCK_MUL_X = 7
TERRAIN_GRID_BLOCK_MUL_Y = 8
# this is the spacing between 32x28 grid blocks, in grid_spacing units
TERRAIN_GRID_BLOCK_SPACING_X = ((TERRAIN_GRID_BLOCK_MUL_X-1)*TERRAIN_GRID_MAVLINK_SIZE)
TERRAIN_GRID_BLOCK_SPACING_Y = ((TERRAIN_GRID_BLOCK_MUL_Y-1)*TERRAIN_GRID_MAVLINK_SIZE)
# giving a total grid size of a disk grid_block of 32x28
TERRAIN_GRID_BLOCK_SIZE_X = (TERRAIN_GRID_MAVLINK_SIZE*TERRAIN_GRID_BLOCK_MUL_X)
TERRAIN_GRID_BLOCK_SIZE_Y = (TERRAIN_GRID_MAVLINK_SIZE*TERRAIN_GRID_BLOCK_MUL_Y)
# format of grid on disk
TERRAIN_GRID_FORMAT_VERSION = 1
IO_BLOCK_SIZE = 2048
IO_BLOCK_DATA_SIZE = 1821
IO_BLOCK_TRAILER_SIZE = IO_BLOCK_SIZE - IO_BLOCK_DATA_SIZE
#GRID_SPACING = 100
def to_float32(f):
'''emulate single precision float'''
return struct.unpack('f', struct.pack('f',f))[0]
LOCATION_SCALING_FACTOR = to_float32(0.011131884502145034)
LOCATION_SCALING_FACTOR_INV = to_float32(89.83204953368922)
def longitude_scale(lat):
'''get longitude scale factor'''
scale = to_float32(math.cos(to_float32(math.radians(lat))))
return max(scale, 0.01)
def diff_longitude_E7(lon1, lon2):
'''get longitude difference, handling wrap'''
if lon1 * lon2 >= 0:
# common case of same sign
return lon1 - lon2
dlon = lon1 - lon2
if dlon > 1800000000:
dlon -= 3600000000
elif dlon < -1800000000:
dlon += 3600000000
return dlon
def get_distance_NE_e7(lat1, lon1, lat2, lon2, format):
'''get distance tuple between two positions in 1e7 format'''
if format == "pre-4.1":
return ((lat2 - lat1) * LOCATION_SCALING_FACTOR, (lon2 - lon1) * LOCATION_SCALING_FACTOR * longitude_scale(lat1*1.0e-7))
else:
dlat = lat2 - lat1
dlng = diff_longitude_E7(lon2,lon1) * longitude_scale((lat1+lat2)*0.5*1.0e-7)
return (dlat * LOCATION_SCALING_FACTOR, dlng * LOCATION_SCALING_FACTOR)
def add_offset(lat_e7, lon_e7, ofs_north, ofs_east, format):
'''add offset in meters to a position'''
dlat = int(float(ofs_north) * LOCATION_SCALING_FACTOR_INV)
if format == "pre-4.1":
dlng = int((float(ofs_east) * LOCATION_SCALING_FACTOR_INV) / longitude_scale(lat_e7*1.0e-7))
else:
dlng = int((float(ofs_east) * LOCATION_SCALING_FACTOR_INV) / longitude_scale((lat_e7+dlat*0.5)*1.0e-7))
return (int(lat_e7+dlat), int(lon_e7+dlng))
def east_blocks(lat_e7, lon_e7, grid_spacing, format):
'''work out how many blocks per stride on disk'''
lat2_e7 = lat_e7
lon2_e7 = lon_e7 + 10*1000*1000
# shift another two blocks east to ensure room is available
lat2_e7, lon2_e7 = add_offset(lat2_e7, lon2_e7, 0, 2*grid_spacing*TERRAIN_GRID_BLOCK_SIZE_Y, format)
offset = get_distance_NE_e7(lat_e7, lon_e7, lat2_e7, lon2_e7, format)
return int(offset[1] / (grid_spacing*TERRAIN_GRID_BLOCK_SPACING_Y))
def pos_from_file_offset(lat_degrees, lon_degrees, file_offset, grid_spacing, format):
'''return a lat/lon in 1e7 format given a file offset'''
ref_lat = int(lat_degrees*10*1000*1000)
ref_lon = int(lon_degrees*10*1000*1000)
stride = east_blocks(ref_lat, ref_lon, grid_spacing, format)
blocks = file_offset // IO_BLOCK_SIZE
grid_idx_x = blocks // stride
grid_idx_y = blocks % stride
idx_x = grid_idx_x * TERRAIN_GRID_BLOCK_SPACING_X
idx_y = grid_idx_y * TERRAIN_GRID_BLOCK_SPACING_Y
offset = (idx_x * grid_spacing, idx_y * grid_spacing)
(lat_e7, lon_e7) = add_offset(ref_lat, ref_lon, offset[0], offset[1], format)
offset = get_distance_NE_e7(ref_lat, ref_lon, lat_e7, lon_e7, format)
grid_idx_x = int(idx_x / TERRAIN_GRID_BLOCK_SPACING_X)
grid_idx_y = int(idx_y / TERRAIN_GRID_BLOCK_SPACING_Y)
(lat_e7, lon_e7) = add_offset(ref_lat, ref_lon,
grid_idx_x * TERRAIN_GRID_BLOCK_SPACING_X * float(grid_spacing),
grid_idx_y * TERRAIN_GRID_BLOCK_SPACING_Y * float(grid_spacing),
format)
return (lat_e7, lon_e7)
class GridBlock(object):
def __init__(self, lat_int, lon_int, lat, lon, grid_spacing, format):
'''
a grid block is a structure in a local file containing height
information. Each grid block is 2048 bytes in size, to keep file IO to
block oriented SD cards efficient
'''
# crc of whole block, taken with crc=0
self.crc = 0
# format version number
self.version = TERRAIN_GRID_FORMAT_VERSION
# grid spacing in meters
self.spacing = grid_spacing
# heights in meters over a 32*28 grid
self.height = []
for x in range(TERRAIN_GRID_BLOCK_SIZE_X):
self.height.append([0]*TERRAIN_GRID_BLOCK_SIZE_Y)
# bitmap of 4x4 grids filled in from GCS (56 bits are used)
self.bitmap = (1<<56)-1
lat_e7 = int(lat * 1.0e7)
lon_e7 = int(lon * 1.0e7)
# grids start on integer degrees. This makes storing terrain data on
# the SD card a bit easier. Note that this relies on the python floor
# behaviour with integer division
self.lat_degrees = lat_int
self.lon_degrees = lon_int
# create reference position for this rounded degree position
ref_lat = self.lat_degrees*10*1000*1000
ref_lon = self.lon_degrees*10*1000*1000
# find offset from reference
offset = get_distance_NE_e7(ref_lat, ref_lon, lat_e7, lon_e7, format)
offset = (round(offset[0]), round(offset[1]))
# get indices in terms of grid_spacing elements
idx_x = int(offset[0] / self.spacing)
idx_y = int(offset[1] / self.spacing)
# find indexes into 32*28 grids for this degree reference. Note
# the use of TERRAIN_GRID_BLOCK_SPACING_{X,Y} which gives a one square
# overlap between grids
self.grid_idx_x = idx_x // TERRAIN_GRID_BLOCK_SPACING_X
self.grid_idx_y = idx_y // TERRAIN_GRID_BLOCK_SPACING_Y
# calculate lat/lon of SW corner of 32*28 grid_block
(ref_lat, ref_lon) = add_offset(ref_lat, ref_lon,
self.grid_idx_x * TERRAIN_GRID_BLOCK_SPACING_X * float(self.spacing),
self.grid_idx_y * TERRAIN_GRID_BLOCK_SPACING_Y * float(self.spacing),
format)
self.lat = ref_lat
self.lon = ref_lon
def fill(self, gx, gy, altitude):
'''fill a square'''
self.height[gx][gy] = int(altitude)
def blocknum(self):
'''find IO block number'''
stride = east_blocks(self.lat_degrees*1e7, self.lon_degrees*1e7, self.spacing, format)
return stride * self.grid_idx_x + self.grid_idx_y
class DataFile(object):
def __init__(self, lat, lon, folder):
if lat < 0:
NS = 'S'
else:
NS = 'N'
if lon < 0:
EW = 'W'
else:
EW = 'E'
self.name = folder + "/%c%02u%c%03u.DAT" % (NS, min(abs(int(lat)), 99),
EW, min(abs(int(lon)), 999))
self.tmpname = folder + "/%c%02u%c%03u.DAT.tmp" % (NS, min(abs(int(lat)), 99),
EW, min(abs(int(lon)), 999))
try:
os.mkdir(folder)
except Exception:
pass
if not os.path.exists(self.name):
self.fh = open(self.tmpname, 'w+b')
else:
self.fh = open(self.name, 'r+b')
def finalise(self):
'''finalise file after writing'''
self.fh.close()
#and rename
os.rename(self.tmpname, self.name)
def remove(self):
self.fh.close()
if os.path.exists(self.name):
os.remove(self.name)
if os.path.exists(self.tmpname):
os.remove(self.tmpname)
def seek_offset(self, block):
'''seek to right offset'''
# work out how many longitude blocks there are at this latitude
file_offset = block.blocknum() * IO_BLOCK_SIZE
self.fh.seek(file_offset)
def pack(self, block):
'''pack into a block'''
buf = bytes()
buf += struct.pack("<QiiHHH", block.bitmap, block.lat, block.lon, block.crc, block.version, block.spacing)
for gx in range(TERRAIN_GRID_BLOCK_SIZE_X):
buf += struct.pack("<%uh" % TERRAIN_GRID_BLOCK_SIZE_Y, *block.height[gx])
buf += struct.pack("<HHhb", block.grid_idx_x, block.grid_idx_y, block.lon_degrees, block.lat_degrees)
buf += struct.pack("%uB" % IO_BLOCK_TRAILER_SIZE, *[0]*IO_BLOCK_TRAILER_SIZE)
return buf
def write(self, block):
'''write a grid block'''
self.seek_offset(block)
block.crc = 0
buf = self.pack(block)
block.crc = crc16(buf[:IO_BLOCK_DATA_SIZE])
buf = self.pack(block)
self.fh.write(buf)
def check_filled(self, block, grid_spacing, format):
'''read a grid block and check if already filled'''
self.seek_offset(block)
buf = self.fh.read(IO_BLOCK_SIZE)
if len(buf) != IO_BLOCK_SIZE:
return False
(bitmap, lat, lon, crc, versionfile, spacing) = struct.unpack("<QiiHHH", buf[:22])
if (versionfile != TERRAIN_GRID_FORMAT_VERSION or
abs(lat - block.lat)>2 or
abs(lon - block.lon)>2 or
spacing != grid_spacing or
bitmap != (1<<56)-1):
return False
buf = buf[:16] + struct.pack("<H", 0) + buf[18:]
crc2 = crc16(buf[:1821])
if crc2 != crc:
return False
return True
def create_degree(downloader, lat, lon, folder, grid_spacing, format):
'''create data file for one degree lat/lon'''
lat_int = int(math.floor(lat))
lon_int = int(math.floor((lon)))
tiles = {}
dfile = DataFile(lat_int, lon_int, folder)
blocknum = -1
while True:
blocknum += 1
(lat_e7, lon_e7) = pos_from_file_offset(lat_int, lon_int, blocknum * IO_BLOCK_SIZE, grid_spacing, format)
if lat_e7*1.0e-7 - lat_int >= 1.0:
break
lat = lat_e7 * 1.0e-7
lon = lon_e7 * 1.0e-7
grid = GridBlock(lat_int, lon_int, lat, lon, grid_spacing, format)
if grid.blocknum() != blocknum:
continue
if dfile.check_filled(grid, grid_spacing, format):
continue
for gx in range(TERRAIN_GRID_BLOCK_SIZE_X):
for gy in range(TERRAIN_GRID_BLOCK_SIZE_Y):
lat_e7, lon_e7 = add_offset(lat*1.0e7, lon*1.0e7, gx*grid_spacing, gy*grid_spacing, format)
lat2_int = int(math.floor(lat_e7*1.0e-7))
lon2_int = int(math.floor(lon_e7*1.0e-7))
tile_idx = (lat2_int, lon2_int)
while not tile_idx in tiles:
tile = downloader.getTile(lat2_int, lon2_int)
waited = False
if (tile == 0 and downloader.offline == 1) or (isinstance(tile, srtm.SRTMOceanTile) and downloader.offline == 1):
#skip tile
dfile.remove()
return False
elif tile == 0:
print("waiting on download of %d,%d" % (lat2_int, lon2_int))
time.sleep(0.3)
waited = True
continue
if waited:
print("downloaded %d,%d" % (lat2_int, lon2_int))
print("Creating for %d %d with spacing %u" % (lat_int, lon_int, grid_spacing))
tiles[tile_idx] = tile
if isinstance(tile, srtm.SRTMOceanTile):
# if it's a blank ocean tile, there's a quicker way to generate the tile
grid.fill(gx, gy, 0)
else:
altitude = tiles[tile_idx].getAltitudeFromLatLon(lat_e7*1.0e-7, lon_e7*1.0e-7)
grid.fill(gx, gy, altitude)
dfile.write(grid)
dfile.finalise()
return True