[SOLVED] How to use NiceSteps in a Βottom Axis
lazarus / 55-TAChart

----------------------------------------------------------------------
donnie · 2017-01-30 11:55

Hi there,
I have a Chart, in which bottom axis is connected with a
DateTimeIntervalChartSource.
(Chart->BottomAxis->Marks->Source->DateTimeIntervalChartSource and
Style->smsLabel).
As to the topic How to Use nice Stps to LeftAxis(http://forum.lazarus.
freepascal.org/index.php/topic,34219.0.html) I have made some values
in order to have marks to let's say every 5 days. The problem is that
if the date range is wide enough it is 'confused'(maybe the mixlength
and maxlength ). I need a general solution e.g. per Day, Week, Month.
The field DateTimeIntervalChartSource -> Steps is refered to the zoom
factor.
I was wondering that if the chart itself can understand that date
range to the zoom factor, maybe that can happen as a variable to nice
steps.
Let's say that we have a chart that it's bottom axis is from
01/10/2016 to 31/12/2016. I am trying to find that parameter that:
If i choose it in days I want to have marks at 01/10,02/10,
03/10...29/12, 30/12, 31/12.
If i choose it in weeks I want to have marks at 01/10,08/10,
15/10...16/12, 23/12, 30/12.
If i choose it in months I want to have marks at 01/10, 01/11, 01/12.

----------------------------------------------------------------------
wp · 2017-01-30 15:43

I was playing a bit with the DateTimeIntervalChartSource in the same
way I did in the LeftAxis thread that you cited. But I did not get an
acceptable solution.

Axis labelling is very complex and depends on many factors, and
data/time axis is even more complex because of the irregular lengths
of months (28/29/30/31 days) and years (365/366 days).

If you have specific labeling requirements then it's best to replace
the DateTimeIntervalchartSource by a standard ListChartSource in which
you store all the labels to be used.

The attached code populates a ListChartSource this way: If the
"autodetect" checkbox is off then you select the date/time units by
means of the combobox; if it is on the program calculates the length
of the displayed axis range and selects an appropriate unit. If labels
are too close and overlap you can increase the SpinEdit to skip a
given number of labels.

Since this is code outside the TAChart library you can modify it as
you like, for example to adjust the format strings.

----------------------------------------------------------------------
donnie · 2017-01-31 13:21

Nice approach wp!
This demo must be added to the TAChart samples for sure!
It is much better with ListChartSource indeed. The autodetect confused
me a bit as it takes consider of the spinedit value and split it to
the maximum possible unit of the bottom axis.
Thanks once again.