40 lines
1.3 KiB
Python
40 lines
1.3 KiB
Python
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import numpy as np
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def visible_cells(h): # calculate visible ERA5 surface cells (30 km x 30 km) as function of balloon height
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if h < 0:
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res = 4
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elif h > 40000:
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res = 2601
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else:
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res = h * 2597/40000 + 4
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return res
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def transform(lon, lat): # longitude and latitude (in degree) to x, y, z (in m) in WGS84 coordinate system
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# WGS 84 reference coordinate system parameters
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a = 6378137.0 # major axis [m]
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e2 = 6.69437999014e-3 # eccentricity squared
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lon_rad = np.radians(lon)
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lat_rad = np.radians(lat)
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# convert to cartesian coordinates
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r_n = a / (np.sqrt(1 - e2 * (np.sin(lat_rad) ** 2)))
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x = r_n * np.cos(lat_rad) * np.cos(lon_rad)
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y = r_n * np.cos(lat_rad) * np.sin(lon_rad)
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z = r_n * (1 - e2) * np.sin(lat_rad)
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return x, y, z
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def radii(lat, h): # get radii to transform local velocity vectors in m/s to change in lat, lon (in deg/s)
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# WGS 84 reference coordinate system parameters
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a = 6378137.0 # major axis [m]
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e2 = 6.69437999014e-3 # eccentricity squared
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lat_rad = np.radians(lat)
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# convert to total distance to center of Earth (used for latitudes)
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r_lat = h + a / (np.sqrt(1 - e2 * (np.sin(lat_rad) ** 2)))
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# determine distance to Earth rotation axis (used for longitudes)
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r_lon = np.cos(lat_rad) * r_lat
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return r_lon, r_lat
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