University of Leeds

IT

Overview of Computer Graphics

Charting

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One of the prime uses for graphical software at the University is to produce graphs and charts.

Everyone has data of one kind or another, whether on paper, in the computer, or just in the mind. We often need to know the significance and properties of the data, or to be able to compare different parts of it against other data sets.

One of the simplest aspects of data display is the production of charts. This is where you would want to put your data into a graphical form to show relationships and comparisons between sets of values. There may be a number of reasons why you would want to put your data into a chart:

  • to illustrate differences between different sets of data

  • to show trends between two variables

  • to show patterns of behaviour in one variable.

There are basically two broad areas of graphs:

  • Presentation charts and graphs of the kind used to illustrate a few principal points. We see these on news and current affairs programs on television. A bar chart or a pie chart is used to indicate results of data obtained so far and the general trends. They are often liberally decorated with bright colours to increase their visual appeal and attractiveness to the viewers and to hold their attention. They are used for visual impact and getting a simple point over clearly and effectively.

  • Scientific charts and graphs are more concerned with ensuring that the detail in the data is represented accurately and faithfully. We may have some results obtained from experimental measurements and wish to display them. We may want to compare the results from the data measurements with the results we would expect according to a particular theoretical model. We may want to draw a curve through the data points (i.e. interpolate the data) and display this along with the original points.

The aims of the two are different, and so the facilities you will want from your charting package will also be different.

Presentation charting has more to do with impressive presentation graphics where the aim is to put a salient point across to an audience. As a result the priority with this sort of charting is not always accuracy of representation. You want charts with strong colours, an impressive look and special effects. The effect of a presentation can be enhanced by using 3D graphs, adding pictures to the graph, or using pictograms. These sorts of charts are rarely produced in isolation but as part of a general presentation. Therefore, some presentation packages also have their own charting module for this purpose. Word and PowerPoint use a module called Microsoft Graph and Excel's charting module has some very powerful presentation graphics features. Origin and Gsharp, both dedicated charting packages, also provide professional presentation charting facilities on the PC systems. Gsharp is also available on the UNIX systems.

In scientific charting you want to display data as accurately as possible in order to analyse it graphically or demonstrate clearly your comparisons and results. As this sort of charting is done mainly for analysis, it is rarely an isolated activity but is often done alongside detailed numerical analysis of your data. Two of the most powerful charting packages available are Origin on the PC network and Gsharp on the PC and UNIX systems. Also, many numerical analysis packages have their own charting modules integrated with the rest of the package.

It is clear that your choice of charting program will depend very much on what purpose you want the chart to fulfil, and also what other programs you are already using. On the whole, if you are already using a program that has its own charting module, use that. The table below gives some rough guidelines on your choice of charting PC package, with the packages increasing in facilities and complexity going down the table.

Requirement

Choice

Simple bar, column, line or pie charts to integrate in a word processor

Microsoft Graph in Word, Charting Module in Excel

Charts for use in a presentation

Microsoft Graph in Word or PowerPoint, Charting Module in Excel, Origin

Raw data requiring good quality scientific charting

Origin, Gsharp

Data requiring simple mathematical or statistical analysis

Charting Module in Excel, Origin, Gsharp

Complicated statistical analysis and good quality scientific charts

Graphics module in SPSS



If you want to do charting on UNIX you are recommended to use the Uniras software and in particular Gsharp.

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