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gsn_polyline

Draws a polyline on the given plot.

Prototype

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"  ; This library is automatically loaded
                                                          ; from NCL V6.2.0 onward.
                                                          ; No need for user to explicitly load.

	procedure gsn_polyline (
		wks  [1] : graphic,  
		plot [1] : graphic,  
		x    [*] : numeric,  
		y    [*] : numeric,  
		res  [1] : logical   
	)

Arguments

wks

A Workstation identifier. The identifier is one returned either from calling gsn_open_wks or calling create to create a Workstation object.

plot

A plot identifier created by using one of the many gsn functions, or by calling create to create a View object.

x
y

One-dimensional arrays of the same length containing the X and Y coordinates of the polyline, and must be in the range of the X/Y coordinates of the data in plot. If drawing the line on a map, then X should correspond to longitude values, and Y to latitude values.

res

A variable containing an optional list of polyline resources, attached as attributes. Set to True if you want the attached attributes to be applied, and False if you either don't have any resources to set, or you don't want the resources applied.

Description

If a missing value is encountered in x and/or y, then this pair is ignored, and the polyline will be disconnected at this pair.

There are many line dash patterns available, and you can use the gsLineDashPattern resource to change the dash pattern. The default is a solid line. You can also create your own dash pattern using the NhlNewDashPattern function.

If you want to resize the plot (i.e., by passing the plot to gsn_panel or setting the vpWidthF or vpHeightF resources), then use the function gsn_add_polyline. This will cause the polyline to be attached to the given plot, and hence automatically resized when the plot is resized.

Note: there is a potential incompatible change in NCL version 6.2.0, when attaching lines or polygons to a map. This change affects gsn_polyline, gsn_add_polyline, gsn_polygon, and gsn_add_polygon.

Previously, drawing a polyline around the equator, for example, could be specified using 2-element arrays. For example:

  lnid = gsn_add_polyline(wks,map,(/0,360/),(/0,0/),lnres)
Now, however, in order to eliminate a number of ambiguous situations and to make user code simpler in most cases, a new behavior has been introduced: the line between two points on the globe always follows the shortest path. In the example above, the behavior in NCL V6.2.0 leads to a 0-length line. The recommended approach now for drawing a line around the equator is to use four points, such that the distance from one to the next is always less than 180 degrees. For example:

  lnid = gsn_add_polyline(wks,map,(/0,120,240,360/),(/0,0,0,0/),lnres)

See Also

gsn_polygon, gsn_polymarker, gsn_polygon_ndc, gsn_polymarker_ndc, gsn_polyline_ndc, gsn_add_polygon, gsn_add_polymarker, gsn_add_polyline, gsn_text, gsn_text_ndc, gsn_add_text, gsn_add_shapefile_polylines, gsn_add_shapefile_polymarkers, gsn_add_shapefile_polygons, NhlNewMarker, NhlNewDashPattern

Examples

Example 1

Draw several horizontal lines on an XY plot and color them separately. We then do this a second time using the more simple gsnYRefLine method:

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"

begin
  wks = gsn_open_wks("x11","line")  ; Open X11 window

;
; Create some dummy data.
;
  npts = 500
  x    = fspan(0,npts-1,npts)
  y    = 500.+ 0.9 * x * sin(0.031415926535898*x)

;
; Set some resources.
;
  xyres             = True     
  xyres@gsnFrame    = False   ; Don't advance frame
  xyres@gsnMaximize = True    ; Maximize plot in frame
;
; Create and draw plot, but don't advance frame just yet.
;
  xy = gsn_csm_y(wks,y,xyres)

;
; Set up some values to add some horizontal lines.
;
  xvalues = (/min(x),max(x)/)
  yvalues = (/     300,     450,  510,   670,    720,    910/)

  colors  = (/"orange","purple","red","blue","brown","green"/)
  nvalues = dimsizes(yvalues)

;
; First way to add lines, using gsn_polyline.
;
  lnres = True
  do i=0,nvalues-1
    lnres@gsLineColor = colors(i)
    gsn_polyline(wks,xy,xvalues,(/yvalues(i),yvalues(i)/),lnres)
  end do

  frame(wks)   ; Now advance frame.
;
; Second way, using gsnYRefLine.
;
  delete(xyres@gsnFrame)
  xyres@gsnYRefLine       = yvalues
  xyres@gsnYRefLineColors = colors

  xy = gsn_csm_y(wks,y,xyres)
end
For some more examples, see:

Also, see the suite of polyline examples.