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cgconlevels.pro

top cgConLevels

Graphics, Utilities

result = cgConLevels(data [, FACTOR=float] [, MAXVALUE=MAXVALUE] [, MINMAX=MINMAX] [, MINVALUE=MINVALUE] [, NLEVELS=integer] [, /SILENT] [, STEP=STEP] [, SUCCESS=boolen])

This program is designed to create "nicely formatted" contour levels for use in contour plots. The idea is to be able to produce evenly spaced contour intervals with the contour levels rounded off to the preferred degree of accuracy. The program will make a "guess" as to how to do this, but users can also take control of the process if the results are not pleasing enough.

There is no claim that this program always produces the best results. It is more of a tool that can produce decent result in many situations.

The program requires the Coyote Library to be installed on your machine.

Return value

A vector of contour levels of the requested number. Each level is rounded to a predefined or specified degree of accuracy.

Parameters

data in required

The data for which contour levels are desired.

Keywords

FACTOR in optional type=float

The program makes a "guess" at how to best round the levels in the data presented to it. This guess is not always what the user wants. This keyword allows the user to "fine tune" the guess, so that it behaves better. See the examples for details on how this keyword can be used. There is some danger, when using the factor keyword that the results will be terrible. Don't dismay! Just try something else.

MAXVALUE in optional

Normally, the levels are calculated using the minimum and maximum values of the input data. The maximum value used in the calculation can be replaced with this value, if you wish. If both the MinValue and MaxValue keywords are used, you do not need to pass the data parameter.

MINMAX out optional

The actual minimum and maximum values used to calculate the levels.

MINVALUE in optional

Normally, the levels are calculated using the minimum and maximum values of the input data. The minimum value used in the calculation can be replaced with this value, if you wish.

NLEVELS in optional type=integer default=10

The number of contour levels desired.

SILENT in optional type=boolean default=0

Set this keyword if you want the program to remain "silent" in the face of errors. If this keyword is set, the user should rely on the Success keyword to determine whether the program completed its work.

STEP out optional

The step size actually used in the program to calculate the levels.

SUCCESS out optional type=boolen

Upon return, will contain a 1 if the program executed succesfully and a 0 otherwise.

Examples

Here is the normal way a contour plot might be created:

   cgDisplay, WID=0
   data = cgScaleVector(cgDemoData(2), 0.1, 4534.5)
   cgLoadCT, 33, NColors=10, Bottom=1
   cgContour, data, NLevels=10, /Fill, /Outline, $
      Position=[0.1, 0.1, 0.9, 0.75], C_Colors=Indgen(10)+1
   cgColorbar, NColors=9, Bottom=1, /Discrete, /Fit, $
      Range=[Min(data), Max(data)], OOB_High=10, OOB_Low='white'

Here is how the same plot might be created with cgConLevels to produce contour levels at 500 step intervals:

   cgDisplay, WID=1
   data = cgScaleVector(cgDemoData(2), 0.1, 4534.5)
   cgLoadCT, 33, NColors=10, Bottom=1
   levels = cgConLevels(data, Factor=100, MINVALUE=0)
   cgContour, data, Levels=levels, /Fill, /Outline, $
      Position=[0.1, 0.1, 0.9, 0.75], C_Colors=Indgen(10)+1
   cgColorbar, NColors=9, Bottom=1, /Discrete, /Fit, $
      Range=[Min(levels), Max(levels)], OOB_High=10, OOB_Low='white'

In this example, the data is scaled so that it is a bit more perverse. The levels have been chosen so they round in the third decimal place:

   cgDisplay, WID=2
   data = cgScaleVector(cgDemoData(2), 0.153, 0.986)
   cgLoadCT, 33, NColors=10, Bottom=1
   levels = cgConLevels(data)
   cgContour, data, Levels=levels, /Fill, /Outline, $
      Position=[0.1, 0.1, 0.9, 0.75], C_Colors=Indgen(10)+1
   cgColorbar, NColors=9, Bottom=1, /Discrete, /Fit, $
      Range=[Min(levels), Max(levels)], OOB_High=10, OOB_Low='white'

It might be better to have the data rounded in the second data place, to the nearest 0.05 value. This can be done with the Factor keyword:

   cgDisplay, WID=3
   data = cgScaleVector(cgDemoData(2), 0.153, 0.986)
   cgLoadCT, 33, NColors=10, Bottom=1
   levels = cgConLevels(data, Factor=0.05)
   cgContour, data, Levels=levels, /Fill, /Outline, $
      Position=[0.1, 0.1, 0.9, 0.75], C_Colors=Indgen(10)+1
   cgColorbar, NColors=9, Bottom=1, /Discrete, /Fit, $
      Range=[Min(levels), Max(levels)], OOB_High=10, OOB_Low='white'

Author information

Author:

FANNING SOFTWARE CONSULTING:

   David W. Fanning
   1645 Sheely Drive
   Fort Collins, CO 80526 USA
   Phone: 970-221-0438
   E-mail: david@idlcoyote.com
   Coyote's Guide to IDL Programming: http://www.idlcoyote.com

Copyright:

History:

Change History:

  Written, 8 December 2011. David W. Fanning

File attributes

Modification date:	Fri Mar 27 11:07:38 2015
Lines:	290
Docformat:	rst rst

Coyote Graphics Routines

Date: Fri Mar 27 12:14:20 2015

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