Line plots

Plotting overview• Plotting procedures: Line plots: plot, oplot, plots, axis Map plots: contour 3-D plots: surface, shade_surf (Putting labels over the plot: xyouts )• When a plotting procedure is called, the default

behavior is as follows:

1. Erase the contents of the current window (a new window is created if none exits)

2. Establish appropriate data coordinates for the input data

3. Draw axes (including labels and tick marks) 4. Draw the data lines

Line plots — Plot • Syntax: plot, x, y plot, y (the data points are plotted against

corresponding array indices) plot, x, y, max=dmax, min=dmin (limit the

maximum and minimum data values to be plotted)

• Overplotting oplot, x, y• Scatter plots plot, x, y, psym=1• Polar plots plot, r, t, /polar

Plot customization• Keywords General: title, charsize, charthick For data lines: linestyle, thick, psym, symsize, color, /nodata, /noerase, /noclip For axis: /ynozero, /xlog, /ylog, [xyz]title, range, style, thick [xyz]ticks, tickv, tickname, ticklen

Creating Axes• The axis procedure may be used to create customized axes on

existing plots. Often used when one or more variables with different units are plotted with respect to the same ordinates

axis, [x or y]axis=[0 or 1], [xy]range= …, [xy]title=…

(where xaxis=0 bottom, xaxis=1 top, yaxis=0 left, yaxis=1 right)

• Example:

t=findgen(11)

g=9.8

v=g*t

x=0.5*g*t^2.0

plot, t, v, /nodata, ystyle=4, xtitle=“Time”

axis, yaxis=0, yrange=[0,100], /save, ytitle=“Velocity”

oplot, t, v

axis, yaxis=1, yrange=[0, 500], /save, ytitle=“Distance”

oplot, t, x, linestyle=2

Multiple panels and plot positioning

• Global system variables

• Multiple panels !p.multi=[0, n_columns, n_rows, 0, 0] To disable multiple panels: !p.multi=0• Plot positioning !p.position=[x1, y1, x2, y2]

Graphic devices• Commonly used graphic devices: X, PS• Select a graphic device set_plot, device_name (‘X’ or ‘PS’)• Configure the graphic device device, filename=file_name, bits_per_pixel=8, /color,

$ /portrait (or /landscape), $ /inches, xsize=xsiz, xoffset=xoff, ysize=ysiz,

yoffset=yoff

Using fonts in postscript• See

http://idlastro.gsfc.nasa.gov/idl_html_help/About_Device_Fonts.html

• You can specify the name, style and size of the letters

plot,[0,1]

device, /times, /bold

xyouts, 0.5, 0.5, ‘bold’

In-class assignment VIIData files are stored at:

http://lightning.sbs.ohio-state.edu/geo820/data/

1. Read the netCDF file sst.mnmean.nc for ERSST data. Plot the SST time series for 0N155E for for 1979-2005, with the corresponding y-axis on the left.

2. Read the HDF file ssmi.hdf. Overplot on the above figure the V10m time series for 0N155E with the corresponding y-axis on the right.

3. Plot four panels on the same page, with each panel containing both the SST and V10m time series for 0N155E, 0N170E, 0N185E, 0N200E