Three coordinate systems are involved when drawing a chart on the screen:
- The inner-most coordinates are the pixels on the screen, TAChart calls them image coordinates.
- The outer-most coordinates are the values plotted on the axes; these are the units of the data values provided by the chart source. In TAChart speak these are called axis coordinates.
- In between these two systems are the graph coordinates. This is an inivisible linear coordinate system layed over the chart. The connection between graph and image coordinates is made by the chart methods GraphToImage and ImageToGraph. The connection between graph and axis coordinates is defined by axis transformations. The axis transformations provide methods GraphToAxis and AxisToGraph. Normally, where there is no transformation, TAChart uses an identity transformation, i.e. assumes graph and axis coorindates to be equal. When the transformations object has been assigned to an axis you can also call the axis' GraphToAxis and AxisToGraph methods. And when a series has been assigned to an axis (by setting its AxisIndexX and/or AxisIndexY) you can also use the series' methods GraphToAxis and AxisToGraph.