Can we specify which values are used for the Axis Labels?

[kimonkremizas]

I have an XYGraph where Y is of type Double and X is of type Long, representing time in EpochMilliseconds. I coded it so that the X Axis Label displays either the year if the value is a timestamp on January 1st or the month otherwise. The issue is that if I can't specify which values should be labeled, the likelihood of January 1st being one of them is minimal when the range spans, for example, 7 years.

So my question can be summed up as: Can we specify which values are used for the labels?

[gsteckman]

The short answer is no. But, if you always know exactly what values your axis will have, you can write an axis model that always provides the tick values you want. But I suspect that's not the situation you have. This would also not adapt the number of tick values depending on the size of the axis.

What if you could put an Annotation on the axis at the position of where the year would be? See #28 . In this case you would use the text of the year as your annotation.

[kimonkremizas]

I think that the Axis Annotation could work, but there might be some overlap with the AxisLabels. Unless they were aware of each other's existence, so e.g. Annotation has priority over Label. Or the idea is to have some vertical padding between them, so there is no overlap?

I just tried to do something similar using the XYAnnotation and the VerticalLineAnnotation. How would 2024 and 2025 be shown along with Nov, Mar, Oct and Feb?

As an alternative, does adding a parameter called e.g. majorTickValues on AxisModel sound like a good idea to you or not?

[gsteckman]

If there is an axis annotation, then it could conceivably overlap with the label. The use case I had in mind for the feature would be to put markers on the axis, e.g. a small triangle or other indicator, which could be drawn with a transparency so as not to completely obscure the labels. For your use case, that would be an issue unless the annotation could be drawn below the axis labels, for example. Since the feature doesn't exist yet, I haven't thought through how it would work and if the annotation size and placement would be used to possibly alter the size of the plot itself.

The AxisModel adjusts the tick values based on the data range provided as well as the current zoom and pan position. If a static set of tick values is provided then they wouldn't get updated when the plot is zoomed or panned.

I think the root of the challenge here is that it's not straightforward to get from milliseconds to the first day of a year. That causes the intervals of the tick values to be strange because it is evenly spacing long values, not dates. The best solution here is probably to have an AxisModel that uses Dates directly. Then it could be more sophisticated in choosing tick values that align with intervals of time, e.g. seconds, days, months, quarters, years.

[kimonkremizas]

You are right, I was not taking zoom and pan into account. And yes, having a time-specific AxisModel would be ideal. For now I got around the year label issue by using the XYAnnotation and the VerticalLineAnnotation as you suggested, but still try to find out if there is a way to have the month labels being shown on the first day of the month instead of a "random" day.

Can you elaborate a bit more on this sentence of yours? Since in my case I don't want to support any zooming/scrolling, maybe this could be a workaround.

But, if you always know exactly what values your axis will have, you can write an axis model that always provides the tick values you want.

[gsteckman]

As an example, if you were always going to plot dates from the year 2024, you could make a custom AxisModel that returns values for the first millisecond of each month in the year. Probably not useful. To do anything much more sophisticated is probably about the same amount of work as making an AxisModel that uses a date type instead of Long.