NCL Home> Application examples> gsn_csm graphical interfaces || Data files for some examples

Example pages containing: tips | resources | functions/procedures

XY Plots

XY Plotting Functions


gsn_xy (generic routine)







Related Pages

  • Bar chart - how to turn XY plots into bar plots
  • Legends - how to add legends to an xy plot
  • Drawing primitives - how to add additional lines, text, markers, and polygons to a plot
xy_1.ncl: Default XY plot.

gsn_csm_xy is the plot template that draws xy plots.

xy_2.ncl: Multiple line plot with varying colors, thicknesses, and markers.

xyLineThicknesses allows the user to change the thickness of individual lines in the array, while xyLineThicknessF allows the user to set one value that changes the thickness of all the lines in the array.

You can set the color of your lines with xyLineColors.

xyMarkLineMode allows the user to set the "mode" ("Lines", "MarkLines", "Markers") for all lines. You can change colors and marker styles with xyMarkerColors and xyMarkers.

There are numerous marker styles to choose from. See example 4 for an example of creating your own markers.

A Python version of the two curve XY plot projection is available here.

xy_3.ncl: Profile plot with y-axis reversed. Demonstrates how to change the line dash pattern.

First Plot: Use predefined dash pattern: xyDashPatterns allows you to select from one of the following dashed patterns. Note that in a multi-line plot, the default is to make the first line the first pattern, the second line the second pattern etc.

trYReverse, reverses the y-axis.

Second Plot: Create your own dash pattern: As of NCL version 4.2.0.a030, you can make your own marker using NhlNewDashPattern. You give the function a string representing the pattern you want. See script and function documentation for examples. The function returns a dash pattern index that can be used with xyDashPatterns

A Python version of the profile plot projection is available here.

xy_4.ncl: Scatter plot

First Plot: Use predefined markers
xyMarkLineModes, xyMarkers, xyMarkerColor, and xyMarkerSizeF are used to control the markers in an XY plot.

Second Plot: Make your own marker
As of NCL version 4.2.0.a030, you can make your own marker using NhlNewMarker. You give the function the character and font table you want the marker taken from, and provide sizing and placement values. The function returns a marker index that can be used with xyMarkerColor.

A Python version of the scatter plot projection is available here.

xy_5.ncl: Adding a polyline and shading above and below it: both color and b&w. Limit axis.

gsn_polyline is the function that will add the polyline. Note that you can not panel plots made with this function. If you need to panel, use gsn_add_polyline. See polyline example 4 on how to use this function. It is slightly different than gsn_polyline.

gsnYRefLine, gsnAboveYRefLineColor, gsnBelowYRefLineColor will draws a reference line and determines the color for the shaded regions.

vpHeightF and vpWidthF will changes the aspect ratio of the plot. Since we stretch the plot, we also moved it slightly to the left using vpXF.

trYMinF, trYMaxF can be used to limit the extent of the y-axis. There are corresponding resources for the x-axis.

A Python version of this projection in color is available here.

xy_6.ncl: Explicit axis labeling

tmXBMode = "Explicit", tmXBValues, adn tmXBLabels will allow the user to explicitly set the tick mark labels for the bottom x (XB) axis. Similar resources exist for the left y (YL) axis etc.

ind returns the indexes of the input where it is True.

ispan allows the user to create an integer array. This is frequently used when creating the x-array in an XY plot.

xy_7.ncl: An example of a double y plot: two separate line with their own unique axis.

gsn_csm_xy2 allows the user to draw two lines each with their own separate Y-axis.

A Python version of the xy_7_2 projection is available here.

xy_8.ncl: Additional axis explicitly set by the user.

tmXUseBottom= False, tmXTOn, and tmXTLabelsOn allows the user to set a top X-axis in addition to the bottom X-axis. We could have done the same for the right Y-axis using the corresponding YR resources.

As in example 6 above, we can now use the explicitly labeling resources tmXTMode = "Explicit", tmXTValues, and tmXTLabels to label the axis.

xy_9.ncl: Turns on grid.

tmXMajorGrid= True, Turns on the grid in the x-direction.
tmXMajorGridThicknessF, controls the line thickness.
tmXMajorGridLineDashPattern, controls the type of line. Similar resources exist for the y-axis grid.

xy_10.ncl: Demonstrates Greek characters into a text string and drawing a polygon around a xy line.

There are numerous fonts/character sets in NCL. As this example demonstrates, you change between sets by using a function code. The default code is a ":", but since this is a character that people often put into their strings, we recommend changing that to a non-used character like a "~". You can change this on the fly as demonstrated in this example, or in your .hluresfile.

A Python version of this projection is available here.

xy_11.ncl: Demonstrates the use of the function gsn_csm_y (available since NCL version 4.2.0.a023) which creates a line plot with no defined x-axis except for array index values.

This example also demonstrates how to set the precision of an additional axis.
tmYRLabelsOn turns on the labels, tmYUseLeft = False, will sure than any settings, such as precision used by the left axis are not used for the right axis. tmYRAutoPrecision = False, turns off the auto precision for the right axis and finally, tmYRPrecision sets the desired precision.

xy_12.ncl: Emphasize part of a line.

Method 1: Break the line up into different parts and draw as it it were multiple lines. This way you can specify the color and style of each segment.

Method 2: Similar to example 14, but demonstrates how to create a polygon around a portion of a xy line in order to highlight it.

A Python version of both projections is available here.

xy_13.ncl: Add error bars using gsn_add_polyline and gsn_add_polymarker.

A Python version of this projection is available here.

xy_14.ncl: Label a line.

xyLabelMode = "Custom", allows the user to label a line.

xyExplicitLabels will set the string to label the line, xyLineLabelFontHeightF sets the label size, and xyLineLabelFontColor sets the color.

xy_15.ncl: Turn off borders and tickmarks on selected sides and demonstrates how to draw tickmarks inward.

tmYRBorderOn = False, will turn off a border while tmYROn = False, will turn off the tickmarks for that side. Corresponding resources exist for the other sides.

tmXBMajorOutwardLengthF set to 0.0 will draw the tickmarks inward. You must do this for the minor tickmarks as well. Separate resources exist for each axis.

xy_16.ncl: Profile plot with polyline, legend and log scaling with explicit labeling.

See the legend example page for a description of the legend resources used in this example as well as other legend resources.

A Python version of the first example profile plot projection is available here.

xy_17.ncl: Demonstrates how to fill the areas between two Y curves uising the special "gsn" resources gsnXYAboveFillColors and gsnXYBelowFillColors.
xy_vert_17.ncl: This example is similar to xy_17.ncl, except it demonstrates how to fill the areas between two X curves using the special "gsn" resources gsnXYLeftFillColors and gsnXYRightFillColors.

These resources were added in NCL V6.4.0.

xy_18.ncl: Demonstrates how to use the special "gsn" resource gsnXYFillColors to fill the area between two curves. Also shows how to manually attach a legend and extra text and the top of the plot.

After all the plot elements are created and attached, this script calls maximize_output to maximize the size of the plot in the frame. This only applies for PS/PDF output.

A Python version of this projection is available here.

xy_19.ncl: Draw three curves, each with a separate Y axis, using gsn_csm_xy3. The second frame shows how to customize the individual curves, and move the rightmost Y axis to the right, using amOrthogonalPosF. The third frame shows how to add your own legend using gsn_create_legend and gsn_add_annotation.
xy_20.ncl: Draw two curves, each with a separate X and Y axis, using gsn_csm_x2y2. This example also shows a way of creating a custom legend using calls to gsn_text and gsn_polyline.
xy_21.ncl: Draw a single curve with three Y reference lines, with a fill above the topmost and below the bottommost lines. The resources used are gsnYRefLine, gsnBelowYRefLineColor, and gsnAboveYRefLineColor.
xy_vert_21.ncl: This example is similar to xy_21.ncl, except it shows how to fill curves based on an X reference line.

The resources used are gsnXRefLine, gsnLeftXRefLineColor, and gsnRightXRefLineColor.

These resources were added in NCL V6.4.0.

xy_22.ncl: Draw a single curve with the left Y axis shifted to the left. This kind of plot can be done multiple ways. In this case, it is done by basically drawing the same plot twice, the second time with the plot shifted to the left and everything turned off but the left Y axis.
axes_3.ncl: Shows various ways that you can control all four axes of a plot. Although this is an XY plot, these techniques apply for contour and vector plots as well.
xy_23.ncl: Shows how to use gsn_attach_plots and the resource gsnAttachPlotsXAxis to attach multiple XY plots along the bottom X axes, and how resizing the base plot will automatically cause all plots to be resized.

Several "tmYR" tickmark resources are set to control the ticks and the labels on the right Y axis. The default is to put tickmarks and labels only on the left axis. To put them on the right only, you need to set (for one) tmYUseLeft to False. The resource tmYRLabelDeltaF is set to 2.0 to move the labels further away from the right tickmarks, and tmYRLabelJust is set to "CenterRight" to right-justify the labels.

xy_24.ncl: Shows how to use special "gsn" resources to fill areas between curves.

The first frame shows how to fill areas between adjacent curves that don't intersect, using gsnXYFillColors. This resource can be an array of color indexes or color names, and should have one fewer colors than you have curves.

The second frame shows how to fill areas between adjacent curves that intersect, using gsnXYAboveFillColors and gsnXYBelowFillColors to indicate the colors where one curve is above or below the other curve. For any areas you don't want filled, you can use "transparent" or -1.

Available in version 5.1.0 and later.

xy_vert_24.ncl: This example is similar to xy_24.ncl, except it shows how to fill between curves that are vertically oriented. This feature was added in NCL V6.4.0.

In the first frame, the gsn_csm_xy function detects that your X values are the multi-dimensional array, so the gsnXYFillColors are applied between the X curves.

The second frame shows how to fill areas between adjacent curves that intersect, using gsnXYRightFillColors and gsnXYLeftFillColors to indicate the colors where one curve is to the right or left of the next curve. These resources were added in NCL V6.4.0.

xy_25.ncl: Shows how to add data (curves) to an existing XY plot.

The first frame shows an XY plot created using gsn_csm_xy2, and the second frame shows a new curve that was added to the plot represented by the right Y axis.

The point of this example is to show how to use the relatively unknown NhlAddData function to add data to an XY plot. This example uses some of the normally-hidden object-oriented features of NCL to create a new data object, and to set additional resources.

You need to use the special "xy2" attribute that is returned from the gsn_csm_xy2 call.

xy_overlay_25.ncl: This example is similar to xy_25.ncl, except it shows how to add the third curve by creating another XY plot and overlaying it on the existing two-curve plot.

  • first frame - the original two-curve plot
  • second frame - the third curve in its own plot
  • third frame - the third curve plot overlaid on the two-curve plot

Note that additional code had to be added to turn off the titles before drawing the three-curve plot.

The third curve is in the same data space as the blue curve of the two-curve plot, which is represented by the "xy2" attribute. When you call overlay, you need to use this attribute as the base plot to overlay on.

xy_26.ncl: This plot is similar to example 25. It shows another method for adding curves to an existing XY plot that has two different Y axes.

The first frame shows an XY plot created using gsn_csm_xy2, and the second frame shows how to add a curve to the data space represented by both Y axes using gsn_add_polyline.

To add curves to the data space of the right Y axis, you need to use the special "xy2" attribute that is returned from the gsn_csm_xy2 call.

unique_10.ncl / unique_10_thicker.ncl: This script shows how to create a series of XY plots attached along the X axes, with gray-filled bars added for emphasis.

The second image is identical, except with thicker plot elements for a nicer looking image. It was created by "unique_10_thicker.ncl".

This is a typical plot that people see in papers of paleoclimate studies.

This example was contributed by Yi Wang of PNNL.

xy_27.ncl: This plot shows how to create an XY plot that contains four curves, each with a separate Y axis. Two of the axes are drawn outside of the plot as single vertical lines.

gsn_csm_xy3 is used to draw the first three curves. The fourth curve is created separately, and added as an annotation using NhlAddAnnotation The Y axis for the fourth curve is also added as an annotation. This allows to you resize the original "plot", and all four curves will be resized accordingly.

Michel Mesquita of the Bjerknes Centre for Climate Research gave us permission to include his script.

xy_28.ncl: This script shows how to draw a hodograph plot, which is a suitable approach in describing diurnal variations in the wind vector at a given point.

This script was contributed by Haoming Chen from LASG/IAP in Beijing, China.

xy_29.ncl: This script demonstrates a use of polymarkers. Each file had approximately 30 years of observations. Observations were available for only few days each year. This displays the range of values each year for one selected ascii file (South Pole).

This script was contributed by Birgit Hassler (NOAA).

axes_4.ncl: This script shows how to replace the default axes in an XY plot with a cartesian coordinate system. This method should also work for contour and vector plots.
xy_30.ncl: This script demonstrates how to make the Y axis irregular by overlaying it on a "blank" plot created with gsn_csm_blank_plot. You need to set trYCoordPoints to the array of irregularly-spaced Y values you want on the Y axis.

gsn_csm_blank_plot won't be available until version 6.0.0, so it's included in this example.

The first frame of this example shows the default plot with a linearly-spaced Y axis, and the second frame shows how to make this axis irregularly spaced.

The "ypts" variable is the array that defines the new spacing on the Y axis.

xy_31.ncl: This example shows how to create several of your own dash patterns.

The first frame uses predefined dashed patterns, which can be hard to distinguish if you make the lines really thick.

The second frame uses dash patterns created with the NhlNewDashPattern function.

Here's what the strings look like for the predefined dash patterns:

  0   "$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$"
  1   "$$$$__$$$$__$$$$__$$$$__$$$$__$$$$__$$$$__$$$$__"
  2   "$__$__$__$__$__$__$__$__$__$__$__$__$__$__$__$__"
  3   "$$$$__$__$$$$__$__$$$$__$__$$$$__$__$$$$__$__"
  4   "$$$$__$_$__$$$$__$_$__$$$$__$_$__$$$$__$_$__"
  5   "$$_$$_$$_$$_$$_$$_$$_$$_$$_$$_$$_$$_$$_$$_$$_$$_"
  6   "$$$_$$$_$$$_$$$_$$$_$$$_$$$_$$$_$$$_$$$_$$$_$$$_"
  7   "$_$$_$_$$_$_$$_$_$$_$_$$_$_$$_$_$$_$_$$_$_$$_$_$$_"
  8   "$_$$$_$_$$$_$_$$$_$_$$$_$_$$$_$_$$$_$_$$$_$_$$$_"
  9   "$$_$$$$_$$_$$$$_$$_$$$$_$$_$$$$_$$_$$$$_$$_$$$$_"
  10  "$$$$_$$_$_$$_$$$$_$$_$_$$_$$$$_$$_$_$$_$$$$_$$_$_$$_"
  11  "$$__$$__$$__$$__$$__$$__$$__$$__$$__$$__$$__$$__"
  12  "$$$$$$__$$$$$$__$$$$$$__$$$$$$__$$$$$$__$$$$$$__"
  13  "$$$_$$$__$$$_$$$__$$$_$$$__$$$_$$$__$$$_$$$__"
  14  "$$___$$___$$___$$___$$___$$___$$___$$___$$___$$___"
  15  "$_$___$_$___$_$___$_$___$_$___$_$___$_$___$_$___"
  16  "$$$$$_____$$$$$_____$$$$$_____$$$$$_____$$$$$_____"
xy_32.ncl: This example shows how to draw a 8-curve XY plot with 4 legends stacked side-by-side.

In order to do this, it is necessary to create 4 XY plots, each with two curves and two items in its legend. The legend for each plot is moved to the right or left slightly so they don't overlap. The plots are then all "connected" into one plot using the overlay procedure.

xy_33.ncl: An ncl-talk question wanted to reproduce a plot created by Excel. This required fairly basic steps: (a) read values from an ASCII (text) file via asciiread; (b) apply a 13-point running average runave; (c) fit a 3rd degree least squares polynomial using lspoly (or lspoly_n) to the output from the running average function; and, (d) plot all three series using a common ordinate array.
mkZmean.ncl: This script creates a panel of four XY plots, with filled curves and a custom legend added to the bottom right plot. It was contributed by Dustin Swales, an associate scientist at NOAA/PSD.
xy_34.ncl: This plot is similar to the one generated by xy_23.ncl. It shows how to draw a series of stacked plots, with the Y axes labeled alternatively on the left and right, and with areas of the first and fourth plots highlighted with filled boxes and text.

The Y location of each plot is changed by setting the vpYF value. The highlighting is done with calls to gsn_add_polygon, gsn_add_polyline, and gsn_add_text.

xy_35.ncl : Illustrates the use of new XYPlot opacity resources (new with NCL 6.4.0):


xy_36.ncl: Illustrates the use of the new X reference line resources added in NCL 6.4.0:


xy_yref_36.ncl: This script is identical to the previous one, except the X and Y arrays are swapped, and this time horizontal reference lines are drawn.


xy_37.ncl: Illustrates how to fill the background area of a plot using gsn_add_polygon.