[olau]

Original Flot maintainer here.

I once had to deal with many million data points for an application. I ended up mip-mapping them client-side.

But regarding sampling, if it's a line chart, you can sample adaptively by checking whether the next point makes a meaningfully visible difference measured in pixels compared to its neighbours. When you tune it correctly, you can drop most points without the difference being noticeable.

I didn't find any else doing that at the time, and some people seemed to have trouble accepting it as a viable solution, but if you think about it, it doesn't actually make sense to plot say 1 million points in a line chart 1000 pixels wide. On average that would make 1000 points per pixel.

[PaulDavisThe1st]

We routinely face this in the audio world when drawing waveforms. You typically have on the order of 10-100k samples per second, durations of 10s-1000s of seconds, and pixel widths of on the order of 1-10k pixels.

Bresenham's is one algorithm historically used to downsample the data, but a lot of contemporary audio software doesn't use that. In Ardour (a cross-platform, libre, open source DAW), we actually compute and store min/max-per-N-samples and use that for plotting (and as the basis for further downsampling.

[leeoniya]

> In Ardour (a cross-platform, libre, open source DAW), we actually compute and store min/max-per-N-samples and use that for plotting (and as the basis for further downsampling.

this is, effectively, what uPlot does, too: https://github.com/leeoniya/uPlot/issues/1119

[ghc]

> Original Flot maintainer here.

I discovered flot during my academic research career circa 2008 and it saved my ass more times than I can count. I just wanted to say thank you for that. I wouldn't be where I am today without your help :)

[leeoniya]

hey!

> But regarding sampling, if it's a line chart, you can sample adaptively by checking whether the next point makes a meaningfully visible difference measured in pixels compared to its neighbours.

uPlot basically does this (see sibling comment), so hopefully that's some validation for you :)

[dapperdrake]

This is a good sampling transform to offer. Call it "co-domain awareness" or something.