Calculate velocities by plate ID

This example calculates velocities at all points in geometries of a collection of features using the plate IDs of those features and a rotation model.

Sample code

import pygplates


# Load one or more rotation files into a rotation model.
rotation_model = pygplates.RotationModel('rotations.rot')

# Load the features that contain the geometries we will calculate velocities at.
# Calling them 'domain' features since using them as input to velocities (but can be any type of feature).
domain_features = pygplates.FeatureCollection('features.gpml')

# Calculate velocities at 10Ma using a delta time interval of 1Ma.
reconstruction_time = 10
delta_time = 1

# All reconstructed geometry points and associated (magnitude, azimuth, inclination) velocities.
all_reconstructed_points = []
all_velocities = []

# Iterate over all geometries in all domain features and calculate velocities at each of their points.
for domain_feature in domain_features:

    # We need the feature's plate ID to get the equivalent stage rotation of that tectonic plate.
    domain_plate_id = domain_feature.get_reconstruction_plate_id()

    # Get the rotation of plate 'domain_plate_id' from present day (0Ma) to 'reconstruction_time'.
    equivalent_total_rotation = rotation_model.get_rotation(reconstruction_time, domain_plate_id)

    # Get the rotation of plate 'domain_plate_id' from 'reconstruction_time + delta_time' to 'reconstruction_time'.
    equivalent_stage_rotation = rotation_model.get_rotation(
            reconstruction_time, domain_plate_id, reconstruction_time + delta_time)

    # A feature usually has a single geometry but it could have more - iterate over them all.
    for geometry in domain_feature.get_geometries():

        # Reconstruct the geometry to 'reconstruction_time'.
        reconstructed_geometry = equivalent_total_rotation * geometry
        reconstructed_points = reconstructed_geometry.get_points()

        # Calculate velocities at the reconstructed geometry points.
        # This is from 'reconstruction_time + delta_time' to 'reconstruction_time' on plate 'domain_plate_id'.
        velocity_vectors = pygplates.calculate_velocities(reconstructed_points, equivalent_stage_rotation, delta_time)

        # Convert global 3D velocity vectors to local (magnitude, azimuth, inclination) tuples (one tuple per point).
        velocities = pygplates.LocalCartesian.convert_from_geocentric_to_magnitude_azimuth_inclination(
                reconstructed_points, velocity_vectors)

        # Append results for the current geometry to the final results.
        all_reconstructed_points.extend(reconstructed_points)
        all_velocities.extend(velocities)

Details

The rotations are loaded from a rotation file into a pygplates.RotationModel.

rotation_model = pygplates.RotationModel('rotations.rot')

The features to calculate velocities at are loaded into a pygplates.FeatureCollection. They can be any type of feature as long as they have a reconstruction plate ID (and of course some geometry).

domain_features = pygplates.FeatureCollection('features.gpml')
The velocities are calculated at geometries reconstructed to their 10Ma positions.
And the velocities are calculated over a 1My interval from 11Ma to 10Ma.
reconstruction_time = 10
delta_time = 1

pygplates.RotationModel enables to calculate both the rotation from present day to 10Ma of a particular tectonic plate relative to the anchor plate (defaults to zero):

equivalent_total_rotation = rotation_model.get_rotation(reconstruction_time, domain_plate_id)

...and the stage rotation from 11Ma to 10Ma:

equivalent_stage_rotation = rotation_model.get_rotation(
        reconstruction_time, domain_plate_id, reconstruction_time + delta_time)
A pygplates.Feature usually contains a single geometry property but sometimes it contains more.
Actually domain_feature.get_geometries() is just a convenient alternative to domain_feature.get_geometry(property_return=PropertyReturn.all).
for geometry in domain_feature.get_geometries():

The geometries extracted from features are in present day coordinates and need to be reconstructed to their 10Ma positions.

reconstructed_geometry = equivalent_total_rotation * geometry
We convert it into a list of pygplates.PointOnSphere to calculate velocities at using pygplates.GeometryOnSphere.get_points().
reconstructed_points = reconstructed_geometry.get_points()
The velocities are calculated at the reconstructed geometry positions (10Ma) using the stage rotation.
This returns a list of pygplates.Vector3D (one global cartesian velocity vector per geometry point).
velocity_vectors = pygplates.calculate_velocities(reconstructed_points, equivalent_stage_rotation, delta_time)
If the velocities need to be in local (magnitude, azimuth, inclination) coordinates then the global cartesian vectors can be converted using pygplates.LocalCartesian.convert_from_geocentric_to_magnitude_azimuth_inclination().
Note that each point in reconstructed_points determines a separate local coordinate system. For example, the velocity azimuth is relative to North as viewed from a particular point position.
velocities = pygplates.LocalCartesian.convert_from_geocentric_to_magnitude_azimuth_inclination(
        reconstructed_points, velocity_vectors)
Finally we add the reconstructed points and velocities to two large lists for all features.
all_reconstructed_points.extend(reconstructed_points)
all_velocities.extend(velocities)

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