[PROJ] Read vertical deflection from egm (96, 08, etc.)

[Fabian Gross]

Dear proj-members,

is there a way to read the vertical deflection (xi, eta) directly with 
proj?

My work-around is sampling the geoid-grid shift:

```python
def get_vertical_deflection(lon, lat):
    """
    take origin and 1 east + 1 north on GEOID, transform to topocentric 
and check
    :param lon: longitude of point of interest on WGS84 (°)
    :param lat: latitude of point of interest on WGS84 (°)
    :return: (xi, eta) deflection in meridional and prime vertical (rad)
    """
    eps = 0.0001  # °
    lons = np.array([lon, lon + eps, lon])
    lats = np.array([lat, lat,       lat + eps])
    geoid_heights = get_geoid_height_egm96(lons, lats)

    # W. E. Featherstone, "The Use and Abuse of Vertical Deflection" p. 4
    e = eccentricity(f_wgs84)
    phi = np.deg2rad(lat)

    # meridional, north/south
    # R_M, should be radius of curvature in the meridian at point of 
interest
    rad_meridian = get_radius_of_curvature_meridian(a_wgs84, e, phi)
    # d_North = R d_lat; in rad
    xi = -(geoid_heights[2] - geoid_heights[0])/(rad_meridian * 
np.deg2rad(eps))

    # prime vertical, east/west
    # R_N, should be radius of curvature in the prime vertical at point of 
interest
    rad_prime_vertical = get_radius_of_curvature_prime_vertical(a_wgs84, 
e, phi)
    # d_East = R cos(lat) d_long; in rad
    eta = -(geoid_heights[1] - geoid_heights[0])/(rad_prime_vertical * 
np.deg2rad(eps) * np.cos(phi))
    return xi, eta

```
Over which (arc) distance should I sample the geoid gtx?

Kind regards

Fabian Gross
Telefon +49 (711) 648 71-995
_________________________________________________
sbp 
schlaich
bergermann partner

Beratende Ingenieure
für erneuerbare Energie

Stuttgart . Berlin . New York
São Paulo . Shanghai . Paris

sbp sonne gmbh

Markus Balz Dipl.Ing. (FH)
Andreas Keil Dipl.Ing.

Schwabstrasse 43
70197 Stuttgart
Telefon +49 (711) 648 71-0

www.sbp.de
_________________________________________________
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/proj/attachments/20190626/9deae0d7/attachment.html>