Chart's X Value of Latest Element

[mje]

I'm stumped here. I have a situation where at run time I need to wipe a chart's history clean and start it anew, but I want all future updates to appear continuous with the x-scale established by previous updates. Basically I need to empty the history array and set an appropriate offset value to the x scale such that all future points are measured relative to my new origin, all the while preserving the existing scale's range.

 

Problem is I can't figure out how to get the last x-value used when only given a chart's refnum. The x scale offset and multiplier properties seem like they would help, but the problem is once the chart history is exhausted, the offset value is never updated. Hence the Offset + Multiplier * History.Length formula only works up until the point the history begins to roll around, after which the calculation returns a constant value.

 

I can't assume the scale's range property reflects the last possible element either...the chart could be in the process of "filling" up rather than scrolling, never mind how the update mode is configured.

 

Surely there's a way of determining the last x value from a chart refnum? I mean the chart needs to either be aware of it or be able to calculate it to render properly, am I blind or is this value not accessible?

 

Note: I know I can get this functioning by using my own counter for number of updates the chart has seen instead of using the length of the history array, but it seems ridiculous to have to carry around duplicate state data like this. Surely I'm missing some obvious property?

[Jordan Kuehn]

Would this accomplish what you are trying to do?  Quick and dirty, but it gets the idea across.

 

Edit// Interesting looks like the snippet tool doesn't care for the linked nodes.

 

Edit x2// Here is CCT capture.  Much better.

[mje]

Negative, that will only work if the chart is set to sweep mode and the chart is full since the scale maximum value doesn't necessarily correspond to the last used x-value. I've attached a VI that demonstrates the behavior I'm after. Note "Method 2" does exactly what I want to do, it just seems redundant to have to duplicate this state information, so I'm wondering if there's a better way?

 

Chart Reset.vi (LV 2012 SP1)

[ShaunR]

Negative, that will only work if the chart is set to sweep mode and the chart is full since the scale maximum value doesn't necessarily correspond to the last used x-value. I've attached a VI that demonstrates the behavior I'm after. Note "Method 2" does exactly what I want to do, it just seems redundant to have to duplicate this state information, so I'm wondering if there's a better way?

 

Chart Reset.vi (LV 2012 SP1)

 

You have forgotten to take into account the X.RngeStart value.

Edited May 29, 2013 by ShaunR