NCL Graphics: Vector Effects

This page shows how to customize vectors using various resources. Here's a sample of a few of them. You can see a full list on the vector resource page.

vcLevelPalette - change the colors used for coloring the vectors by magnitude or another field
vcLineArrowThicknessF / vcWindBarbLineThicknessF - thicken vectors or wind barbs; the default line thickness may be too thin for large displays
vcMinDistanceF - thin the vectors by specifying a minimum allowable distance between them
vcFillArrowFillColor / vcFillArrowEdgeColor - change the look of filled arrows
vcGlyphOpacityF - adjust the opacity/transparency of the vectors

veceff_1.ncl: This script compares a default vector plot (first frame) with vector plots that have been customized (second and third frames). The second frame customizes the plot by setting the following resources:

vcRefLengthF - changes the length of the reference vector
vcMinFracLengthF - sets the length of the smallest vector as a fraction of the reference vector
vcMonoLineArrowColor - setting to False colors the vectors based on magnitude
vcLevelPalette - changes the colors used for the vectors

The third frame increases the line thickness of the vectors using vcLineArrowThicknessF. This can be especially important if you need to make images large for presentations or posters.

veceff_2.ncl: Sets the size of the arrow heads.

This example is similar to the previous one, except the size of the arrow heads are made the same by setting vcLineArrowHeadMinSizeF and vcLineArrowHeadMaxSizeF to the same value.

veceff_3.ncl: Controlling the appearance of vector arrow heads.

vcFillArrowFillColor and vcFillArrowEdgeColor enable you to set the color and outline color of filled vectors.

The second and third frames show how to further control the appearance of the arrow heads using a whole set of resources: vcFillArrowWidthF, vcFillArrowMinFracWidthF, and vcFillArrowHeadMinFracXF.

veceff_4.ncl: Thinning vectors.

Use vcMinDistanceF to thin your vectors based the distance between vectors.

You can also thin your vectors simply by striding the data:

  vector = gsn_csm_vector(wks,u(::2,::2),v(::2,::2),res)

newcolor_8.ncl: This example demonstrates drawing partially transparent filled vectors.

The vectors are drawn fully opaque in the first frame. In the second frame, vcGlyphOpacityF is set to 0.3.