Is this possible? I tried

gridSurface.InteractivityStyles.Add(yIndex, String.Format("({0}, {1}) {2}", xIndex, zIndex, yData[yIndex++]));

but get an incompatibility message. 

Hi Kevin,

You have to pass a NInteractivityStyle object instead of string, but in general it is better to use the collection indexer, like this:

gridSurface.InteractivityStyles[yIndex] = new NInteractivityStyle("some string");


If you intend to use the same formatting for all surface data points, it is much better to use the series's interactivity style object:

gridSurface.InteractivityStyle = new NInteractivityStyle("(<xindex>, <zindex> ) <value>");

As you know <xindex> <zindex> and <value> are predefined tags that are internally replaced with the respective values for the selected surface data point.

Best Regards,
Nevron Support Team

Thanks - is there a list of tags somewhere in the Help? What I'd like to do here is use the axis labels instead of the grid indexes. I can add each tooltip manually but it would be great if there was a tag for this.

Most of the series related topics in the documentation contain sections called "Formatting commands" that specify the tags that can be used for particular series types. You can check the topics under:

Chart for .NET \ User's Guids \ Chart Types

especially:

One Value Series Functionality
XY Scatter Series Functionality
XYZ Scatter Series Functionality
Series Test Formatting

The tags can be used to insert series values and calculated values in the data labels or the legend. For now it is not possible to insert axis scale values.

Best Regards,
Nevron Support Team