Support HeatMap

[bhaskarvk]

Options

• https://www.patrick-wied.at/static/heatmapjs/plugin-leaflet-layer.html / https://github.com/pa7/heatmap.js/tree/develop/plugins/leaflet-heatmap
• https://github.com/Leaflet/Leaflet.heat (This is from the Leaflet guys)
• https://github.com/ursudio/webgl-heatmap-leaflet

I'm leaning towards #3 as it has performance benefits over the other two.

[bhaskarvk]

closed in 488de06

[RCura]

After trying a lot to use this library, I'm now convinced that it's not satisfying enough for a real use:

• The original library hasn't evolved in years ;
• some of the functions that probably worked years ago do not anymore, for example gradientTextures that doesn't work (heatmap remains black, check the original example), and thus doesn't allow to change the default colors ;
• heatmap.blur() and heatmap.multiply() can't be applied live : layer has to be removed, changed and added again.

In comparison, Leaflet.heat is way more reliable, considering it's developed by Leaflet authors and more actively maintained.

As for the perfomances, I did some benchmark using the feature/heatmap branch of rstudio/leaflet and comparing it to this WebGLHeatmap binding, for different size datasets :

• small : 10k random points
• medium : 100k random points
• big : 500k random points

Benchmark files

• Leaflet.heat small
• Leaflet.heat medium
• Leaflet.heat big
• WebGLHeatmap small
• WebGLHeatmap medium
• WebGLHeatmap big

Benchmark results

Framework	Size	Time (s)
Leaflet.heat	Small	1.14
Leaflet.heat	Small	1.14
Leaflet.heat	Small	1.16
Leaflet.heat	Small	1.20
Leaflet.heat	Small	1.13
-----------	------	------
WebGLHeatmap	Small	1.32
WebGLHeatmap	Small	1.35
WebGLHeatmap	Small	1.41
WebGLHeatmap	Small	1.38
WebGLHeatmap	Small	1.32
-----------	------	------
Leaflet.heat	Medium	1.60
Leaflet.heat	Medium	1.63
Leaflet.heat	Medium	1.65
Leaflet.heat	Medium	1.61
Leaflet.heat	Medium	1.68
-----------	------	------
WebGLHeatmap	Medium	1.70
WebGLHeatmap	Medium	1.83
WebGLHeatmap	Medium	1.83
WebGLHeatmap	Medium	2.23
WebGLHeatmap	Medium	2.19
-----------	------	------
Leaflet.heat	Big	3.23
Leaflet.heat	Big	3.17
Leaflet.heat	Big	3.22
Leaflet.heat	Big	3.29
Leaflet.heat	Big	3.23
-----------	------	------
WebGLHeatmap	Big	3.29
WebGLHeatmap	Big	3.17
WebGLHeatmap	Big	3.29
WebGLHeatmap	Big	3.21
WebGLHeatmap	Big	3.14

This shows that for such datasets, there is no significant differences in load time. I also checked memory use (js heap), and the result is also approximately the same.

For all those reasons, I'd like Leaflet.heat to be considered worthy of being added to leaflet.extras, as I think it would be a big asset for this package, and for R spatial analysts in general.

[bhaskarvk]

@RCura Thanks for the detailed comparison. I'll integrate leaflet.heat soon.

[bhaskarvk]

@RCura Some more comments
Recently I fixed some performance issues in the WebGL heatmap code (see #42), have you tried with the revised code for your benchmarking ?
I know why gradientTextures doesn't work (CORS issue) and in theory should be fixable.

I will integrate Leaflet.heat but just wanted to make sure your benchmarking is done against the latest code base.

[RCura]

@bhaskarvk : I ran those tests like 2-3 days ago, and used the github version of leaflet.extras, so, this commit was taken into account :)
The performance boost probably affects larger datasets, that I haven't been testing here as I'm looking for "real-time" exploration :)

As for the gradientTextures, I'm glad you found :)
It seems to have been bugging for years (see that issue : pyalot/webgl-heatmap#7), and the author seems to have abandonned this repo (this PR hasn't been answered in 1 year), so, I don't know how/if you want to correct it, but a fresh fork might be a good option :)

Thanks for your work 😀

[bhaskarvk]

Cool thanks for the confirmation. You've certainly made a solid case for Leaflet.heat :)

[Vishan07]

Great to read that Leaflet.heat will be integrated. Do you have an expectation as to when this will be available?

[dutchminator]

I'd like to add my vote for integrating leaflet.heat.
@bhaskarvk Do you have an ETA more specific than "soon" on when you will be able to implement it? Is there any way we can assist you with this?

[bhaskarvk]

I'll start working on this today, so hopefully before the start of next week.