Plot: Support multiple X/Y series

[ljburtz]

Hello, migrating from plotjuggler to foxglove but a currently blocking use case is comparing robot odometry calculated by the robot to a ground truth

for this I need to display an x/y plot -> top down map (the x axis is the odometry x, the y axis is the odometry y. there is no timestamp indexing as in a regular time series)

this works great in foxglove for a single plot by using "msg path accumulated) as an index (see screenshot, blue line)

However, I can't find out how to display two (or three) overlapping robot trajectories on the same plot = to compare the robot's odometry estimate with the ground truth

See screenshot of this feature in plotjuggler -> x/y plots make it very intuitive to compare estimated trajectories to ground truth two different trajectory estimates, drifting away from the ground truth as the robot travels

Thanks!

[ljburtz]

Maybe in foxglove parlance these types of x/y plots are a separate panel type? Something closer to the Map panel? But not using a NavSatFix message (longitude / latitude) but simple x and y coordinates pairs from selectable topic's message field?

basically the Map panel is overkill for many use cases (that don't use longitude/latitude) and the current plot panel is best for timeseries where the plot's x axis is a timestamp, not a coordinate

[ljburtz]

this issue also adrresses the feature request in #1393 of 1 year ago! :pray: