AP_Terrain: added script for creating terrain *.dat files

useful for pre-populating a microSD card

libraries/AP_Terrain/tools/create_terrain.py

@@ -0,0 +1,299 @@
+#!/usr/bin/env python
+'''
+create ardupilot terrain database files
+'''
+
+from MAVProxy.modules.mavproxy_map import srtm
+import math, struct, os, sys
+import crc16, time, struct
+
+# 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
+
+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 get_distance_NE_e7(lat1, lon1, lat2, lon2):
+    '''get distance tuple between two positions in 1e7 format'''
+    return ((lat2 - lat1) * LOCATION_SCALING_FACTOR, (lon2 - lon1) * LOCATION_SCALING_FACTOR * longitude_scale(lat1*1.0e-7))
+
+def add_offset(lat_e7, lon_e7, ofs_north, ofs_east):
+    '''add offset in meters to a position'''
+    dlat = int(float(ofs_north) * LOCATION_SCALING_FACTOR_INV)
+    dlng = int((float(ofs_east) * LOCATION_SCALING_FACTOR_INV) / longitude_scale(lat_e7*1.0e-7))
+    return (int(lat_e7+dlat), int(lon_e7+dlng))
+
+def east_blocks(lat_e7, lon_e7):
+    '''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)
+    offset = get_distance_NE_e7(lat_e7, lon_e7, lat2_e7, lon2_e7)
+    return int(offset[1] / (GRID_SPACING*TERRAIN_GRID_BLOCK_SPACING_Y))
+
+def pos_from_file_offset(lat_degrees, lon_degrees, file_offset):
+    '''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)
+    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])
+
+    offset = get_distance_NE_e7(ref_lat, ref_lon, lat_e7, lon_e7)
+    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))
+
+    return (lat_e7, lon_e7)
+            
+class GridBlock(object):
+    def __init__(self, lat_int, lon_int, lat, lon):
+        '''
+        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)
+
+        offset = (round(offset[0]), round(offset[1]))
+
+        # get indices in terms of grid_spacing elements
+        idx_x = int(offset[0] / GRID_SPACING)
+        idx_y = int(offset[1] / GRID_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(GRID_SPACING),
+                                        self.grid_idx_y * TERRAIN_GRID_BLOCK_SPACING_Y * float(GRID_SPACING))
+        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)
+        return stride * self.grid_idx_x + self.grid_idx_y
+
+class DataFile(object):
+    def __init__(self, lat, lon):
+        if lat < 0:
+            NS = 'S'
+        else:
+            NS = 'N'
+        if lon < 0:
+            EW = 'W'
+        else:
+            EW = 'E'
+        name = "terrain/%c%02u%c%03u.DAT" % (NS, min(abs(int(lat)), 99),
+                                        EW, min(abs(int(lon)), 999))
+        try:
+            os.mkdir("terrain")
+        except Exception:
+            pass
+        if not os.path.exists(name):
+            self.fh = open(name, 'w+b')
+        else:
+            self.fh = open(name, 'r+b')
+
+    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)
+        return buf
+
+    def write(self, block):
+        '''write a grid block'''
+        self.seek_offset(block)
+        block.crc = 0
+        buf = self.pack(block)
+        block.crc = crc16.crc16xmodem(buf)
+        buf = self.pack(block)
+        self.fh.write(buf)
+
+    def check_filled(self, block):
+        '''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, version, spacing) = struct.unpack("<QiiHHH", buf[:22])
+        if (version != 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.crc16xmodem(buf[:1821])
+        if crc2 != crc:
+            return False
+        return True
+
+def create_degree(lat, lon):
+    '''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)
+
+    print("Creating for %d %d" % (lat_int, lon_int))
+
+    total_blocks = east_blocks(lat_int*1e7, lon_int*1e7) * TERRAIN_GRID_BLOCK_SIZE_Y
+
+    for blocknum in range(total_blocks):
+        (lat_e7, lon_e7) = pos_from_file_offset(lat_int, lon_int, blocknum * IO_BLOCK_SIZE)
+        lat = lat_e7 * 1.0e-7
+        lon = lon_e7 * 1.0e-7
+        grid = GridBlock(lat_int, lon_int, lat, lon)
+        if grid.blocknum() != blocknum:
+            continue
+        if not args.force and dfile.check_filled(grid):
+            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)
+                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:
+                        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))
+                    tiles[tile_idx] = tile
+                altitude = tiles[tile_idx].getAltitudeFromLatLon(lat_e7*1.0e-7, lon_e7*1.0e-7)
+                grid.fill(gx, gy, altitude)
+        dfile.write(grid)
+
+from argparse import ArgumentParser
+parser = ArgumentParser(description='terrain data creator')
+
+parser.add_argument("lat", type=float, default=-35.363261)
+parser.add_argument("lon", type=float, default=149.165230)
+parser.add_argument("--force", action='store_true', help="overwrite existing full blocks")
+parser.add_argument("--radius", type=int, default=100, help="radius in km")
+parser.add_argument("--debug", action='store_true', default=False)
+parser.add_argument("--spacing", type=int, default=100, help="grid spacing in meters")
+args = parser.parse_args()
+
+downloader = srtm.SRTMDownloader(debug=args.debug)
+downloader.loadFileList()
+
+GRID_SPACING = args.spacing
+
+done = set()
+
+for dx in range(-args.radius, args.radius):
+    for dy in range(-args.radius, args.radius):
+        (lat2,lon2) = add_offset(args.lat*1e7, args.lon*1e7, dx*1000.0, dy*1000.0)
+        lat_int = int(round(lat2 * 1.0e-7))
+        lon_int = int(round(lon2 * 1.0e-7))
+        tag = (lat_int, lon_int)
+        if tag in done:
+            continue
+        done.add(tag)
+        create_degree(lat_int, lon_int)
+
+create_degree(args.lat, args.lon)