On 7/13/16, 7:38 AM, "Elvis Stansvik" <elvst...@gmail.com> wrote:
> Hi Adam, > 2016-06-27 21:55 GMT+02:00 Thompson, Adam B. <thompso...@ornl.gov>: > > The software package I co-develop at work is dependent on Qt 4.8, but we > > plan to move to Qt 5 when we have time/funding. We currently depend on a > > third-party plotting package for our 2D data visualization, but we'd like to > > be able to use QtCharts when we upgrade. > > > > > > > > Some of our data sets are time-dependent and are often extrapolated hundreds > > or thousands of years in the future. As such, a logarithmic time scale would > > be quite useful, if not necessary to view the data in a truly meaningful > > manner. > > > > > > > > Can anyone provide guidance on properly extending QDateTimeAxis (, > > QLogValueAxis, or QAbstractAxis) to provide a logarithmic time scale as I've > > described? > > I have not used QtCharts at all myself yet, but from looking at the > classes you mentioned, I don't think there's a way to combine the > functions of QDateTimeAxis and QLogValueAxis to get what you want. > Also note, that even if this had been possible, there's this > limitation (from the QDateTimeAxis) docs: > > "QDateTimeAxis works correctly with dates from 4714 BCE to 287396 > CE. There are also other limitiation related to QDateTime. Please > refer to QDateTime documentation." > > Which may or may not be a problem for you. > > What you probably have to do is to create a custom axis type, deriving > the QAbstractAxis that you mentioned. You could of course have a look > at the source of QDateTimeAxis and QLogValueAxis for inspiration. > > Time, and especially calendar systems, is a tricky business, but > depending on your requirements, you may not have to deal much with > that. > > A possibility may be to use a QLogValueAxis as your internal > representation, to leverage some of its functionality. But since it > works with floating point numbers, I think I'd rather make my own that > works with an integer type as internal representation of time. > > Sorry I can't be of more help, but I think deriving QAbstractAxis to > implement a custom axis type is what you'll have to do. > > Elvis Elvis, Thank you for your response. True, there are potential limitations to keep in mind when attempting to display dates far into the future. The documentation for QDateTime (http://doc.qt.io/qt-5/qdatetime.html) mentions a much larger supported range of values, so I find that a little confusing. If there were a way to use QLogValueAxis but provide custom labels, that would easily suffice, but I don’t see a way to do that, either. Those types depend on private classes derived from QAbstractAxisPrivate, but I wouldn’t be able to extend that myself since it’s declared in a private header and implemented in qabstractaxis.cpp. The same goes for extending QLogValueAxis(Private) or QDateTimeAxis(Private). Adam Thompson Computer Scientist, Nuclear Engineering Oak Ridge National Laboratory +1.865.241.8062 _______________________________________________ Interest mailing list Interest@qt-project.org http://lists.qt-project.org/mailman/listinfo/interest
