DataPlotter - linear or logarithmic display of 2D data

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Introduction

The DataPlotter is a .NET control for graphical display of 2D data. For both the X and Y axis a linear or logarithmic (any base) scaling can be selected. Also for both axis the data range can be specified.

Maybe it is of interest to somebody else out there. At least it can be used as another sample on how to fiddle with GDI+ in .NET.

Background

For charting in the .NET world there is still the good old MSChart ActiveX control or you have to buy one of the new .NET controls on the market.

Since neither the MSChart control made me happy for my purpose nor did I want to spend money, I decided to start something on my own. This project is nothing fancy or new -- it's just my first steps in .NET graphics.

Using the code

The implementation of DataPlotter is quite simple: It's a .NET Windows control library with a bunch of properties. Everything else happens in the OnPaint function.

These are the properties:

A few hints on some properties:

• The borders define the inner axis rectangle. Use bigger borders on the left and bottom to have enough space for the scaling numbers.
• If a LogBase property is below 2 then a linear scaling is selected. Otherwise the number is the base for logarithmic scaling. Typically use 0 for linear and 10 for logarithmic scales.
• For logarithmic scaling, use full decades for the RangeStart and RangeEnd properties, e.g. 0.01 to 1000 for a LogBase of 10.
• The Data arrays must be of the same size of course.

A short walkthrough of the OnPaint function:

• Check the property values for consistency.
• Prepare the graphical tools. There are pens for the graph, grid lines and axis and a brush for scale numbering.
• The inner axis rectangle is calculated by deducting the border properties from the client rectangle size.
• The grid lines are drawn for X and Y directions. Here also the scale numbers are written.
• Then the axis rectangle is created.
• The data arrays are transformed into an array of points. The values from RangeStart to RangeEnd are mapped onto points of the axis grid considering the LogBase scales. Invalid points (detected by exception handler) are skipped by reusing the last valid point.
• The points are drawn according to the DrawMode.

The DataPlotter is an assembly that can be used as shown in the DataPlotterTest application. This demo has four buttons with sample data for the possible linear/logarithmic scalings. There is also a property grid so see/change the DataPlotter's properties.

Where to go from here

The current implementation of DataPlotter served my purpose quite well. But there are many useful extensions and enhancements I can think of:

• Use more than one set of data to be drawn in different colors in the same diagram.
• Add description properties like title, names for the axis etc.
• Extend draw modes, e.g. dotted or dashed lines etc.

Help yourself and let me know about your own enhancements.