opendrift.readers.basereader.unstructured

Module Contents

Classes

UnstructuredReader

An unstructured reader. Data is gridded irregularily.

Attributes

logger

opendrift.readers.basereader.unstructured.logger

class opendrift.readers.basereader.unstructured.UnstructuredReader

Bases: opendrift.readers.basereader.variables.Variables

An unstructured reader. Data is gridded irregularily.

The initial type of grid that this class supports are triangular prisms. Unstructured in xy-coordinates, x and y is constant in z. z might be non-cartesian (e.g. sigma-levels).

See also

opendrift.readers

structured.StructuredReader

PARALLEL_WORKERS

boundary

x

y

node_variables

nodes_idx

xc

yc

face_variables

faces_idx

abstract get_variables(variables, time=None, x=None, y=None, z=None)

Obtain and return values of the requested variables at all positions (x, y, z) closest to given time.

Returns:

Dictionary with arrays of length len(time) with values at exact positions x, y and z.

_get_variables_interpolated_(variables, profiles, profiles_depth, time, reader_x, reader_y, z)

This method _must_ be implemented by every reader. Usually by subclassing one of the reader types (e.g. structured.StructuredReader).

Arguments are in _native projection_ of reader.

_build_boundary_polygon_(x, y)

Build a polygon of the boundary of the mesh.

Arguments:

param x:

Array of node x position, lenght N

param y:

Array of node y position, length N

Returns:

A shapely.prepareped.prep shapely.Polygon.

The boundary of the mesh, ideally including holes in the mesh.

Algorithms:

Note

Try this alogrithm: https://stackoverflow.com/a/14109211/377927

Boundary edges (line between two nodes) are only referenced by a single triangle.

1. Find a starting edge segment: [v_start, v_next] (v is vertex or node)

2. Find another _unvisited_ edge segment [v_i, v_j] that has either v_i = v_next or v_j = v_next and add the one not equal to v_next to the polygon.

3. Reset v_next to the newly added point. Mark edge as visited.

4. Continue untill we reach v_start.

The polygon has a rotation, but this should not matter for our purpose of checking the bounds.

Note: In order to find holes in the polygon all points must be scanned.

Approximate using the convex hull:

An alternative simple approximation is to use the convex hull of the points, but this will miss points along the boundary which form a wedge in the boundary (as well as holes in the mesh).

Holes in the mesh will often be covered by the landmask anyway, so they will usually not be a problem.

covers_positions(x, y, z=0)

Check which points are within boundary of mesh.

_build_rtree_(x, y)

Builds an R-tree of x, y

_build_ckdtree_(x, y)

__nearest_ckdtree__(idx, x, y)

Return index of nearest point in cKDTree

static __nearest_rtree__(idx, x, y)

Take array of points and get nearest point in rtree index.

_nearest_node_(x, y)

Return nearest node (id) for x and y

_nearest_face_(xc, yc)

Return nearest element or face (id) for xc and yc