6 Replies Latest reply on Dec 20, 2017 1:38 AM by Adi Bannady

    Interpolated Data on a trend in PI Vision

    telston

      Is there a way to make data not interpolate between two points but still show a trend line, instead of a stepped trend line?

       

      For example, we have samples that are sampled monthly.  We DO NOT want interpolated data in between the two points, but the step feature is not ideal for viewing our data.  We would like the trend to look like it would if it was graphed in Excel instead.

       

      Thanks!

        • Re: Interpolated Data on a trend in PI Vision
          jru

          Hi Tiffany,

           

          I'm a little confused by the request.  Typically, if you need to draw a line between 2 events on a graph you can either draw an interpolating line/curve between the events (depending on what order of interpolation, e.g. linear, quadratic) or a stepped plot if the events are discrete.

           

          Are you looking for a curved line?  Can you perhaps send a screenshot of what you are after?

           

          ~Jesse

            • Re: Interpolated Data on a trend in PI Vision
              telston

              I am looking for a graph that looks more like what you would see if it was graphed in Excel, but DOES NOT show the interpolated values in between.  The data I am looking to graph is laboratory data and it is not ideal to interpolate between two points but the stepped graph doesn't look the way we want.  I have included an example of the same data plotted in Excel for reference. 

               

              Thanks!

               

                • Re: Interpolated Data on a trend in PI Vision
                  jru

                  Hi Tiffany,

                   

                  Here's a plot from PI Vision:

                  Here, I'm plotting a line from point-to-point.  I think that's what you are after?

                   

                  Essentially, Vision will draw a line from point-to-point by default.  The tricky part comes down to your data resolution.  If you have too many data points on the trend, Vision will draw lines to significant points.  That's probably why there's "interpolating" behavior.  Here's a visual guide of what i mean.  This is the same PI Tag with larger time context:

                  As you can see, you don't see the nuances as the trend above.  This is because the size of the trend does not support that many data points. 

                   

                  Essentially, the more data points you have in the trend range, the more your trend looks like it's interpolating.

                   

                  ~Jesse

                    • Re: Interpolated Data on a trend in PI Vision
                      telston

                      That is kind of what I am after.  Although, when you scroll through the data in PI Vision, it shows the interpolated data value.  That is what I am hoping to get ride of.  Does that make sense?  See below.  These data points at this specific time period does not exist but is instead interpolated.  That's what we want to get away from so as not to confuse our users.

                       

                        • Re: Interpolated Data on a trend in PI Vision
                          jru

                          Hi Tiffany,

                           

                          I see what your saying now.  Currently no, there is no supported method to get exactly what you need.

                           

                          I think this inherently comes done to how graphs are interpreted.  Usually, with a line graph, my expectation is that the data is continuous and should be interpolated even if there was no actually data point is there.  Because of a line, I can go between 2 data points and estimate with some degree of accuracy the value at a specific point.

                           

                          On the same token, stepped plots allow us to interpret graphs as if values are discrete and not continuous.  This is because a horizontal line infers that we are not changing the value at all in between data points.  The downside is that the viewing pleasure is not always the best.

                           

                          With regards to your actual request, there are ways to help get exactly what you want.  This will require you to alter some of the scripting files in the Vision Installation.  That being said, these changes will affect ALL trends not just the trends you don't want to have an interpolated value.  Therefore, I would only pursue this route if you do not plan to have that trace line display values ever.   Finally, because you are altering the scripting file, Vision would no longer be in a supported state.  OSIsoft can't guarantee that your changes will not cause any unexpected behaviors or that it will still work after upgrades.  If you still want to go with this option, you should contact tech support at: Contact Us

                           

                          I think the more appropriate solution/feature request would be to have a trend format option to either disable the trace for that trend or only show the data points without the connecting lines.  If that's the case, please create an enhancement request at Customer Feedback for OSIsoft & the PI System.

                           

                          Please let me know if you have any questions or need clarification

                           

                          ~Jesse

                      • Re: Interpolated Data on a trend in PI Vision
                        Adi Bannady

                        I presume you would like to see the actual value(or the previous value) when you hover over the trend instead of the interpolated data. This can be accomplished using custom symbols.

                         

                        -Adi