iOS & macOS Charting Documentation - SciChart iOS & macOS Charts SDK v4.x

Axis 3D APIs - Convert World to Data coordinates

SciChart iOS 3D provides a clean and simple API to transform 3D world coordinates to data-values and vice versa via the ISCIAxisCore.currentCoordinateCalculator API. The ISCICoordinateCalculator has the following methods suitable for conversions:

-[ISCICoordinateCalculator getCoordinateFrom:] - expects a double representation of data-value and returns the corresponding pixel coordinate.
-[ISCICoordinateCalculator getDataValueFrom:] - expects a coordinate in pixels and returns the closest data value to that coordinate (represented in double).

NOTE: For more information about ISCICoordinateCalculator - please read the Axis APIs - Convert Pixel to Data coordinates article.

World Coordinates

All Axes are responsible for converting between data-values and world-coordinates:

X-Axis converts X data-values to X-World coordinates.
Y-Axis converts Y data-values to Y-world coordinates.
Z-Axis converts Z-data values to Z-world coordinates.

NOTE: For more information about the World Coordinates and Data Coordinates - please see the corresponding sections in the Coordinates in 3D Space article.

Getting a CoordinateCalculator instance

There is a ISCIAxisCore.currentCoordinateCalculator property, which is readonly, and which provides a coordinate calculator instance which is only valid for the current render pass.

NOTE: If the ISCIAxisCore.visibleRange changes, the ISCIChartSurface3D.worldDimensions changes or the data changes - then the ISCICoordinateCalculator will be recreated under the hood, so it might give incorrect results. Hence, it’s advisable not to cache CoordinateCalculator instance, or cache it only for a short period of time, e.g. when using inside a loop.

Converting between World to Data Coordinates

As mentioned above - data-values are converted to world coordinates via the -[ISCICoordinateCalculator getCoordinateFrom:] method. Also, Coordinates in pixels are converted back to chart data-values via the -[ISCICoordinateCalculator getDataValueFrom:] method.

Also, you might guess, converting World to Data-Coordinates and vice versa slightly differs for different axis types due to difference in underlying data-types. In particular the following ones:

SCINumericAxis3D
SCIDateAxis3D

Read on to get better understanding of such conversions.

SCINumericAxis3D conversions

The simplest case is the SCINumericAxis3D. ISCICoordinateCalculator for NumericAxis 3D works the data-value as double. So let’s take our Scatter Chart 3D example, and try do some conversions

Scatter Chart 3D

    id<ISCICoordinateCalculator> calculator = yAxis.currentCoordinateCalculator;
    float coordinate = [calculator getCoordinateFrom:50];
    
    // Convert back:
    double dataValue = [calculator getDataValueFrom:coordinate];

    let calculator = yAxis.currentCoordinateCalculator!
    let coordinate = calculator.getCoordinate(50)
    
    // Convert back:
    let dataValue = calculator.getDataValue(coordinate)

    var calculator = yAxis.CurrentCoordinateCalculator;
    var coordinate = calculator.GetCoordinate(50);

    // Convert back:
    var dataValue = calculator.GetDataValue(coordinate);

_{^{Y-Axis: VisibleRange = [-100, 100], Data-Value = 50, Pixel(World)-Coordinate = 149.25}}

NOTE: The exact data-values and coordinates might differ depending on your visibleRange, viewport etc…

SCIDateAxis3D conversions

Similarly to SCINumericAxis3D - the SCIDateAxis3D is quite simple with one difference - it’s ISCICoordinateCalculator works with double representation of Date, which is timeIntervalSince1970. So let’s take our Date Axis 3D as an example, and try do some conversions.

NOTE: Since the ISCICoordinateCalculator works with double representation of Date in timeIntervalSince1970, you will need to do all the needed conversions on your own. See the code below:

Date Axis 3D

    id<ISCICoordinateCalculator> calculator = zAxis.currentCoordinateCalculator;
    NSDate *date = [NSDate dateWithYear:2011 month:5 day:5];
    float coordinate = [calculator getCoordinateFrom:date.timeIntervalSince1970];
    
    // Convert back:
    double intervalSince1970 = [calculator getDataValueFrom:coordinate];
    NSDate *dateValue = [NSDate dateWithTimeIntervalSince1970:intervalSince1970];

    let calculator = zAxis.currentCoordinateCalculator!
    
    let date = NSDate(year: 2011, month: 5, day: 5)!
    let coordinate = calculator.getCoordinate(date.timeIntervalSince1970)
    
    // Convert back:
    let intervalSince1970 = calculator.getDataValue(coordinate)
    let dateValue = Date(timeIntervalSince1970: intervalSince1970)

    var calculator = zAxis.CurrentCoordinateCalculator;
    var date = new DateTime(2011, 5, 5);
    var coordinate = calculator.GetCoordinate(date.ToUnixTime());

    // Convert back:
    var intervalSince1970 = calculator.GetDataValue(coordinate);
    var dateValue = NSDate.FromTimeIntervalSince1970(intervalSince1970).FromDate();

_{^{Z-Axis: VisibleRange = [2019-05-01, 2019-05-08], Data-Value = “2019-05-05”, Pixel(World)-Coordinate = 170.857132}}

NOTE: The exact data-values and coordinates might differ depending on your visibleRange, viewport etc…