TAChart is a package for drawing graphs, charts and other diagrams. It is comparable in features, but not specifically compatible, with Delphi TeeChart package. One substantial difference is that some features (e.g. data sources and axis transformations) are implemented via separate components instead of just properties. This leads to increased flexibility and opportunity for code re-use, but at the cost of some additional API complexity.
Coordinates and axises
TAChart uses three coordinate systems:
- Axis coordinates (known in some other applications as object coordinates) -- this is the "raw" coordinate values obtained from the data. As the name implies, axis coordinates are interpreted in therms of specific axis -- the same coordinate value may have different meaning depending on the axis it is applied to.
- Graph coordinates (aka world coordinates) are converted from the axis coordinates using axis transformation, such as logarithmic scale. Graph coordinates are common for all objects in the chart.
- Image coordinates (aka screen coordinates) are converted from graph coordinates based on the chart viewport. This transformation is always linear and can be influenced by chart tools such as zooming and panning.