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.
You can add or remove arbitrary number of axises by editing
By default, chart have two axises: one horizontal and one vertical.
They are accessible via
Note that those properties are aliases to
so if you remove those default axises, accessing
LeftAxis will return nil.
Axis transformations are grouped in
It contains a list of transformations which are applied in the order given.
For transformations to have an effect, you should:
- Make sure
Enabledproperty is true for all transformations.
- Assign transformations component to
Transformationsproperty of at least one axis.
AxisIndexYproperties of the series to the appropriate axis index.
Note that by default,
AxisIndexY have a special value of -1,
which means "ignore axis transformations". Also note that if you add or remove axises, the indexes may change.
You can rotate the series by assigning both
AxisIndexX to vertical axis and
to the horizontal axis.
To display several independently scaled series, assign them to two or more axises
TAutoScaleAxisTransform to each axis.
See "axistransf" demo, page "Linear", checkbox "Auto scale".
MaxValue properties you can control the in graph coordinates
of the auto-scaled series. For example, by setting one transformation to a range from 0 to 1, and another
to a range from 1 to 2, you will confine all the series using the first transformation to the upper half of the chart,
and all the series using the second transformation to the lower half (assuming there are no unassigned series left).