Skip to content

Grid

Sample grids.

Grid

Bases: BaseModel

Create and fill an integer grid.

Parameters:

Name Type Description Default
grid_id str

unique ID

 required
size int

grid XY size

 required
spacing_ float

grid cell spacing

 required
grid list

grid values

 <dynamic>
lat0 float

southernmost latitude

 0.0
lon0 float

westernmost longitude

 0.0
Source code in src/snailz/grid.py 
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
class Grid(BaseModel):
    """Create and fill an integer grid."""

    _id_gen: ClassVar[utils.id_gen] = utils.id_gen("G", 4)

    grid_id: str = Field(
        min_length=1, description="unique ID", json_schema_extra={"primary_key": True}
    )
    size: int = Field(gt=0, description="grid XY size")
    spacing_: float = Field(gt=0, description="grid cell spacing")
    grid: list = Field(default_factory=list, description="grid values")
    lat0: float = Field(default=0.0, description="southernmost latitude")
    lon0: float = Field(default=0.0, description="westernmost longitude")

    @staticmethod
    def make(params):
        """Make grids."""

        origins = _grid_origins(params)
        result = []
        for lat0, lon0 in origins:
            grid = Grid(
                grid_id=next(Grid._id_gen),
                size=params.grid_size,
                spacing_=params.grid_spacing,
                lat0=lat0,
                lon0=lon0
            )
            grid.fill()
            result.append(grid)
        return result

    @staticmethod
    def tidy(grids):
        """Convert all grids to tidy table."""

        result = [["grid_id", "x", "y", "lat", "lon", "pollution"]]
        for g in grids:
            for x in range(g.size):
                for y in range(g.size):
                    if g[x, y] > 0:
                        lat, lon = g.lat_lon(x, y)
                        result.append([g.grid_id, x, y, lat, lon, g[x, y]])
        return result

    def __getitem__(self, key):
        """Get grid element."""

        x, y = key
        return self.grid[y * self.size + x]

    def __setitem__(self, key, value):
        """Set grid element."""

        x, y = key
        self.grid[y * self.size + x] = value

    def __str__(self):
        """Convert to CSV string."""

        result = []
        for y in range(self.size - 1, -1, -1):
            result.append(",".join([str(self[x, y]) for x in range(self.size)]))
        return "\n".join(result)

    def fill(self):
        """Fill in a grid."""

        center = self.size // 2
        size_1 = self.size - 1
        x, y = center, center

        self.grid = [0 for _ in range(self.size * self.size)]
        while (x != 0) and (y != 0) and (x != size_1) and (y != size_1):
            self[x, y] += 1
            m = random.choice(MOVES)
            x += m[0]
            y += m[1]


    def lat_lon(self, x, y):
        """Calculate latitude and longitude of grid cell."""

        lat = self.lat0 + (y * self.spacing_) / METERS_PER_DEGREE_LAT
        meters_per_degree_lon = METERS_PER_DEGREE_LAT * math.cos(math.radians(self.lat0))
        lon = self.lon0 + (x * self.spacing_) / meters_per_degree_lon
        return lat, lon

make(params) staticmethod

Make grids.

Source code in src/snailz/grid.py 
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
@staticmethod
def make(params):
    """Make grids."""

    origins = _grid_origins(params)
    result = []
    for lat0, lon0 in origins:
        grid = Grid(
            grid_id=next(Grid._id_gen),
            size=params.grid_size,
            spacing_=params.grid_spacing,
            lat0=lat0,
            lon0=lon0
        )
        grid.fill()
        result.append(grid)
    return result

tidy(grids) staticmethod

Convert all grids to tidy table.

Source code in src/snailz/grid.py 
50
51
52
53
54
55
56
57
58
59
60
61
@staticmethod
def tidy(grids):
    """Convert all grids to tidy table."""

    result = [["grid_id", "x", "y", "lat", "lon", "pollution"]]
    for g in grids:
        for x in range(g.size):
            for y in range(g.size):
                if g[x, y] > 0:
                    lat, lon = g.lat_lon(x, y)
                    result.append([g.grid_id, x, y, lat, lon, g[x, y]])
    return result

__getitem__(key)

Get grid element.

Source code in src/snailz/grid.py 
63
64
65
66
67
def __getitem__(self, key):
    """Get grid element."""

    x, y = key
    return self.grid[y * self.size + x]

__setitem__(key, value)

Set grid element.

Source code in src/snailz/grid.py 
69
70
71
72
73
def __setitem__(self, key, value):
    """Set grid element."""

    x, y = key
    self.grid[y * self.size + x] = value

__str__()

Convert to CSV string.

Source code in src/snailz/grid.py 
75
76
77
78
79
80
81
def __str__(self):
    """Convert to CSV string."""

    result = []
    for y in range(self.size - 1, -1, -1):
        result.append(",".join([str(self[x, y]) for x in range(self.size)]))
    return "\n".join(result)

fill()

Fill in a grid.

Source code in src/snailz/grid.py 
83
84
85
86
87
88
89
90
91
92
93
94
95
def fill(self):
    """Fill in a grid."""

    center = self.size // 2
    size_1 = self.size - 1
    x, y = center, center

    self.grid = [0 for _ in range(self.size * self.size)]
    while (x != 0) and (y != 0) and (x != size_1) and (y != size_1):
        self[x, y] += 1
        m = random.choice(MOVES)
        x += m[0]
        y += m[1]

lat_lon(x, y)

Calculate latitude and longitude of grid cell.

Source code in src/snailz/grid.py 
 98
 99
100
101
102
103
104
def lat_lon(self, x, y):
    """Calculate latitude and longitude of grid cell."""

    lat = self.lat0 + (y * self.spacing_) / METERS_PER_DEGREE_LAT
    meters_per_degree_lon = METERS_PER_DEGREE_LAT * math.cos(math.radians(self.lat0))
    lon = self.lon0 + (x * self.spacing_) / meters_per_degree_lon
    return lat, lon

_grid_origins(params)

Generate non-overlapping lower-left (lat, lon) corners for grids.

Source code in src/snailz/grid.py 
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
def _grid_origins(params):
    """
    Generate non-overlapping lower-left (lat, lon) corners for grids.
    """

    grid_width_m = params.grid_size * params.grid_spacing
    stride_m = grid_width_m + params.grid_gap
    cols = math.ceil(math.sqrt(params.num_grids))
    meters_per_degree_lon = METERS_PER_DEGREE_LAT * math.cos(math.radians(params.lat0))

    origins = []
    for i in range(params.num_grids):
        dx = (i % cols) * stride_m
        dy = (i // cols) * stride_m
        origins.append(
            (
                params.lat0 + dy / METERS_PER_DEGREE_LAT,
                params.lon0 + dx / meters_per_degree_lon,
            )
        )

    return origins