# Ngl.streamline

Creates and draws a streamline plot.

## Prototype

plot = Ngl.streamline(wks, u, v, res=None)

## Arguments

*wks*

The identifier returned from calling **Ngl.open_wks**.

*u*,

*v*

The U and V components of the streamlines. *u* and *v*
should be two-dimensional NumPy arrays or NumPy masked arrays
(dimensioned *ny* x *nx*).

*res=None*

An (optional) instance of the Resources class having PyNGL resources as attributes.

## Return value

*plot*

A PlotId representing the streamline plot created.

## Description

This function creates and draws a streamline plot on the given
workstation and advances the frame. Plot options can be set via the
*res* variable.

If coordinate values for the X and Y axes are not available, then index values will be used on the axes.

If axes coordinate information is available, then set the *vfXArray* resource to the one-dimensional
NumPy array (of length *nx*) that represents the X axis, and
*vfYArray* to the one-dimensional
NumPy array (of length *ny*) that represents the Y axis. Or,
you can optionally send some end point values via the resources
*vfXCStartV*, *vfXCEndV*, *vfYCStartV*, *vfYCEndV* resources.

As of version
1.3.0, if *u* and/or *v* are masked arrays,
then any values equal to the corresponding fill values will not be
plotted. If *u* and/or *v* are not masked arrays and
they contain missing values, then set the resources *vfMissingUValueV* and/or *vfMissingVValueV* to these values.

Note that PyNGL internally sets some resources for you, depending on how other resources are set. See the list of default settings for more information.

## See Also

**Ngl.streamline_map**,
**Ngl.streamline_scalar**,
**Ngl.streamline_scalar_map**,
**Ngl.vector**,
**Ngl.vector_scalar**,
**Ngl.vector_map**,
**Ngl.vector_scalar_map**

StreamlinePlot resources

VectorField resources

Title resources

TickMark resources

Transformation resources

View resources

Transform resources

PlotManager resources

Special "ngl" resources

## Examples