I'm using the Chart component in MIT App Inventor to display data. The data and the chart’s displayed values are not changing, but the line style itself changes over time — it starts as a curve, and then slowly becomes a straight line. Does anyone know why this is happening and how I can keep the line consistently as a curve?
（AS THE VIDEO）
Thanks in advance for any help.
Can you upload an aia file to demonstrate this issue.
Please keep the aia as easy/simple as possible.
If I’m not wrong, you are adding the same points repeatedly
chart02.aia (2.7 KB)
Yes,i need to update my data by this way
As docs says old values are not deleted…
We are wandering into advanced statistics here.
Keeping the old data might be changing the estimation technique used to extrapolate the curves between points.
If you love the curves, perhaps just graph the most recent n data points?
But what i want is check if the data is updated ,just like heartbeat. So i try to get the data from my web database repeatedly.
So delete any points older than the last 10 points from your graph.
Sample app graphing only recent points:
After sleeping on your question I remembered some of my math.
There are techniques to derive the coefficients of an nth degree polynomial from a collection of n points.
So one point gives you a flat line, two points gives you a tilted line, three points gives you a parabola, more points gives you more smooth lumps in your curve.
This process becomes unwieldy when you reach too many points.
That's why you want to load your curvy graph from only a few recent data points.
A global list variable can be used as a vestibule or conveyor belt to act as the graph source, flushing and refreshing the graph from the length limited source as each new point arrives.