Vertical Datums

This tutorial will work through converting between different vertical datums and finding gravity values. To learn more about vertical datums refer to the GDA2020 technical manual.

Converting Between Vertical Datums

GeodePy allows you to convert between different vertical datums within Australia. Below we will convert from an ellipsoidal height to AHD and then to AVWS.

import geodepy.height

First we will convert from ellipsoidal height to AHD.

rl = geodepy.height.GPS_to_AHD(
    -35.34405212, #lat
    149.15847673, #long
    594.495 #ellipsoidal height
)

print(rl[0])

>>[575.176]

This is the AHD height. Now we can convert to AVWS.

rl = geodepy.height.AHD_to_AVWS(
    -35.34405212, #lat
    149.15847673, #long
    rl[0] #AHD
)

print(rl[0])

>>[575.303]

Finding Gravity Values

GeodePy can also find gravity values at any point around Australia. This can be seen below.

import geodepy.height

To find the gravity at any point the mean_surface_grav function can be used. Normally this function is used to find the mean surface gravty between two points, however if the same lat and long are used for both point A and B then the gravity at a set location can be found.

grav = geodepy.height.mean_surface_grav(
    -35.34405212, #lat of A
    149.15847673, #long of A
    575.176, #AHD
    -35.34405212, #lat of B
    149.15847673, #lat of B
    575.176 #AHD
)

print(grav)

>>[9.79603591]

To calculate the average gravity between the ellipsoid and a certain height the following function can be used.

grav = geodepy.height.mean_normal_grav(
    -35.34405212, #lat
    594.495 #ellipsoid height
)

print(grav)

>>9.79671297