# Ngl.streamline_scalar

Creates and draws a streamline plot with the streamlines colored by a scalar field.

*Available in version 1.3.0 or later.*

## Prototype

st = Ngl.streamline_scalar(wks, u, v, data, 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 array or NumPy masked arrays
(dimensioned *ny* x *nx*).

*data*

The scalar data field for coloring the streamlines (dimensioned
*ny* x *nx*).

*res=None*

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

## Description

This function creates and draws a streamlines, colored by a scalar field,
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* (*sfXArray*) resource to the one-dimensional
NumPy array (of length *nx*) that represents the X axis, and
*vfYArray* (*sfYArray*) 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* (*sfXCStartV*), *vfXCEndV* (*sfXCEndV*), *vfYCStartV* (*sfYCStartV*), *vfYCEndV* (*sfYCEndV*) resources.

As of version
1.3.0, if *u*, *v*, and/or *data* are
masked
arrays, then any values equal to the corresponding fill
values will not be plotted. If *u*, *v*, and/or
*data* are not masked arrays and they contain missing values,
then set the resources *vfMissingUValueV*, *vfMissingVValueV*, and/or *sfMissingValueV* 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**,
**Ngl.streamline_map**,
**Ngl.streamline_scalar_map**,
**Ngl.vector**,
**Ngl.vector_scalar**,
**Ngl.vector_map**,
**Ngl.vector_scalar_map**

StreamlinePlot resources

ContourPlot resources

VectorField resources

ScalarField resources

LabelBar resources

Title resources

TickMark resources

Transformation resources

View resources

Transform resources

PlotManager resources

Special "ngl" resources