IDL 8.0 Graphics: A
Primer in the new
Graphical System
Jonathan Fairman
UAH Atmospheric Science
3/4/11 and 3/7/11
Short Course
What’s new in IDL 8.0?
New graphics system
 New plotting routines
 New mapping routines
 New contour routines
 New vector routines
 Ability to do streamlines!
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Overview
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New System Introduction
Changes to PLOT
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Annotations: TEXT, LEGEND
 New routines: BARPLOT, ERRORPLOT
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Changes to CONTOUR
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Changes to IMAGE
Changes to MAP
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MAPGRID, MAPCONTINENTS
New Routines
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COLORBAR
VECTOR, STREAMLINE
Bugaboos with new routines
So, what’s this new system,
anyways?
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Functional graphics
 Old
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IDL direct graphics were procedural
Aspects of iPlot tools/object graphics systems
Scriptable
Dynamic Plot Changes without redrawing
Smart saving images
Old direct graphics system still works, so your
code will still produce the plots
However, some things are worth merging over
Graphics basis
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No need to set device keywords
Opens new window with white background automatically
Stores graphical variables in memory, dynamically addressable
LaTeX-like syntax for special characters
Colors are stored in the system
Symbols are stored in the system
Can use text to specify symbols and colors (versus old specification
of numbers)
Let’s start with just introducing the WINDOW
W1 = window()
PLOT
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Old code:
Device, decomposed=0, retain=2
!p.background = 255
Loadct, 39, /silent
Window, 0, xs=600, ys=600
Plot, findgen(10), color=0, /nodata
oplot, findgen(10), color=250
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New Code:
P=plot(findgen(10), color=‘red’,$
dimensions=[600,600])
PLOT
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Properties:
Under the old code, had to specify everything in one statement, e.g.:
Plot, findgen(33)/16*!pi, sin(findgen(33)/16*!pi), color=0,
xrange=[0,2*!pi], $
yrange=[-1,1], charsize=2.0, ystyle=1, xstyle=1 , $
ytitle=‘Y = sin(x), xtitle =‘ x = [0,2!7p!8]’,/nodata
oplot, findgen(33)/16*!pi, sin(findgen(33)/16*!pi), color=250, thick=2
Oplot, findgen(33)/16*!pi, sin(findgen(33)/16*!pi), psym=3, color=0
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New code is dynamic – can set things separately as well as together
P1=plot(findgen(33)/16*!pi, sin(findgen(33)/16*!pi))
P1.color=‘red’
P1.xrange=[0,2*!pi]
P1.ytitle=‘Y = sin(x)’
P1.xtitle =‘x = [0, 2$\pi$] ;this is equivalent to:
P1.symbol=‘plus’
P1.sym_color=‘black’
P1 = plot(findgen(33)/16*!pi, sin(findgen(33)/16*!pi), color=‘red’,$
xrange=[0,2*!pi, ytitle=‘y = sin(x)’, xtitle=‘x = [0, 2$\pi$],$
symbol=‘plus’
Annotations
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LEGEND: uses plot data to make legend,
replacing old method of PLOTS and XYOUTS
TEXT: outputs text to screen (analogue:
XYOUTS)
Create multiple plots with differing names
Use annotations.pro from collections
BARPLOT
Draws a bar plot of data
 Syntax:
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 B1
= BARPLOT(x, y)
Old syntax for bar plots in
make_precip_barplot.pro
 Let’s go to the code…
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ERRORPLOT
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Specification:
 E1
= ERRORPLOT(x,y,xerror,yerror)
 Draws
a box and whisker plot
 All plot keywords the same
 Find
the code in make_precip_error.pro
CONTOUR
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Similar to other plotting systems, but with a twist!
Nonfilled contours similar to changes in PLOT system
Filled contours a little different…
Old code:
Loadct, 39, /silent
Max1 = max(data)
Min1 = min(data)
Contour, data, x, y, nlevels=251, /cell_fill,
levels=findgen(251)/250.*(max1-min1) – min1, color=0
New code:
C1 = contour(data,x,y,n_levels=251,/fill, rgb_table=39)
COLORBAR
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Remember how much of a pain making colorbars was? Not anymore!
Old code:
Ncolors=255
Loc = [0.1,0.1,0.8,0.125]
xsize= (loc(2) – loc(0))*D.X_VSIZE
Ysize = (loc(3) – loc(1))*D.Y_VSIZE
Xstart = loc(0)*D.X_VSIZE
Ystart = loc(3) *D.Y_VSIZE
Bar = BINDGEN(256)#REPLICATE(1B,10)
Bar = BYTSCL(bar, top=ncolors-1)
TV, CONGRID(bar, xsize, ysize), xstart+1, ystart=1
PLOT, findgen(251)/250., findgen(251)/250.*max1, /nodata, $
position=loc, yticks=1, ytickformat=‘(A1)’ yminor=1, xticklen=0.25,$
xrange=[min1,max1], xtitle=title1, color=0, /noerase, xstyle=1
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New code:
Loc = [0.1,0.1,0.8,0.125]
cbar1 = colorbar(target = c1, position = loc)
CONTOUR and COLORBAR
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Let’s go to the code… looking at the wind
speed example
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contour_windspeed.pro
IMAGE
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Replaces TV, does some other stuff as well…
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Context:
Im1 = image(bands, xval, yval, order=1)
Old code:
Tv, bands, xval, yval, order=1, true=3
-Still need order command to make things look right if you don’t rotate it
-automatically senses if it’s a 3-band overlay (no more true=3)
-Saves via im1.save, no more write_png, etc.
MAP
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Most overhauled routine
Moves it into more GIS/ENVI type mapping versus IDL
direct mapping
Calling context:
M1 = map(‘Equirectangular’, limit = [min(lat),
min(lon), max(lat), max(lon)],
position=[0.1,0.1,0.9,0.9], dimension=[900,900]
Replaces:
Map_set, limit = [min(lat), min(lon), max(lat),
max(lon)], position = [0.1,0.1,0.9,0.9]
MAP
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The MAP command also leads to changes in MAPGRID and MAPCONTINENTS
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Start a map…
M1 = map(‘Geographic’, limit=[10,-130,50,-60], dimensions=[900,600])
Now, let’s change some properties…
Mg1 = m1.mapgrid
Mg1.linestyle = ‘Dash’
Mg1.label_position = ‘0’
Mg1.font_size=14
;now, let’s add some continents
Mc1 = mapcontinents(/countries)
Mc1 = mapcontinents(/usa)
;now let’s change some properties!
M1[‘Longitudes’].label_angle=0
M1[‘Ohio’].fill_color=‘red’
M1[‘Michigan’].fill_color=‘blue’
MAP
The map works in projection space, not in
the direct space anymore
 So, let’s say we want to plot points in the
map… of the NARR grid or something
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Let’s go to plot_narr_latlon.pro
VECTOR and STREAMLINE
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Two new ways to plot wind features!
Some of these are pretty awesome!
Context:
V1 = vector(uwind, vwind, x, y,
vector_style=‘barbs’)
St1 = streamline(uwind, vwind, x, y,
streamline_stepsize=0.1, streamline_nsteps=200)
Let’s go to the code: start with stream_vector.pro
Combination plots!
OK, so we have covered mapping,
plotting, streamlines, vectors, colorbars…
 Now let’s put some of these together in
IDL 8.0 syntax.
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Let’s look at combo_plot.pro and go from
there…
Bugaboos
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Some issues that I haven’t figured out yet
More then these, just a brief synopsis
MAP
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CONTOUR
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Filled contours have issue with fixed tables
Can be slow to save in EPS
COLORBAR
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Inability to switch to decimal degrees
Haven’t quite figured out how to map a satellite image yet
Can’t specify position, automatically defined based on projection
Problems with multiple maps in the same window
Can’t change range- specified in data
PLOT
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Multiple axes can be slow if it’s not a direct multiplier
Skew-T in the new plotting system would be a nightmare
Overview
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IDL 8.0 makes simple things easier!
IDL 8.0 makes complex things harder!
Overall, adapt code as you see fit- I’m moving
most of my new simple plotting (especially error
and bar plots) to the new system, but will
probably keep the old Direct Graphics for
mapping and filled contours