Added polyline offset plugin support with example data and script

[fermumen]

Pull Request

Hi,

I have implemented https://github.com/bbecquet/Leaflet.PolylineOffset which is great for visualizing directional road flows on road networks. I was wondering if this would be the best way to share the work with the community.

Essentially I modify the layers file and js sources to accept 'offset' as a variable and add new dependencies for the plug-in

Best regards, Fernando

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:white_check_mark: fermumen
:x: Fernando Munoz Mendez

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[fermumen]

@trafficonese I've gone through your comments hopefully you'll be able to install it and test it now.

[fermumen]

I decided to do without corunaroads as it's probably a bit redundant. Somehow running document() has created a conflict on map-shiny.Rd. Any idea why?

[trafficonese]

I think it is because of the new roxygen version. But you should be able to look at the conflicts, resolve them and merge the results.

[fermumen]

@trafficonese The R checks are ok but as you said we are not passing the Javascript one. I'm a bit out of my depth in JS, unfortunately. It is entirely possible that I haven't properly followed these steps? I'm not sure since I prepared the pull request in April last year and I don't remember 😅

[trafficonese]

Unfortunately i'm no JS-Pro either and I dont know exactly what the checks are doing. But did you use yarn build ? This should build a fresh /htmlwidgest/leaflet.js. Its not included in your PR so you probably skipped that part :)

[schloerke]

Yes. Calling yarn build in the terminal will be necessary for the JS check to pass.

[fermumen]

Success! Thanks @schloerke and @trafficonese, the fresh yarn build did the trick.

[trafficonese]

I have a little suggestion:

Could you include the leafletPolylineoffsetDependencies only if an offset is used? Otherwise the dependency is always added, but not always needed/required.

So if offset is 0/NULL/NA, dont include the dependency.

[fermumen]

For some reason, I'm getting some error when installing, but I think is entirely due to my machine: ERROR: dependency 'leaflet.providers' is not available for package 'leaflet'

I'll try to fix it but in the meanwhile, I haven't been able to install the package and test the new modifications.

Edit: I installed the latest dev version of 'leaflet.providers' I'm not sure why it stopped working but I'm guessing it could be an issue with MRAN

[fermumen]

It looks like the Polylineoffset dependency is being added to the maps regardless we use leafletPolylineoffsetDependencies or not. Any idea why?

[AntonWijbenga]

Are issues with lines becoming circles or other erratic shapes solved in this version? The issues are discussed in the issue list of the bbecquet repository. For example here: https://github.com/bbecquet/Leaflet.PolylineOffset/issues/1

I once adjusted a fork that had fixed such issues and made it compatible with the never version fo Leaflet (v2?). I use ShinyJS to include the .js source and then just use the offset parameter in the addPolylines function. Example: addPolylines(..., options=list(offset=3), ...) which works.

The JS file I use can be found here: https://traphx.maptm.nl/leaflet.polylineoffset_arw.js

I have limited experience with package building and/or JavaScript. Otherwise I'd give it a go myself.

[fermumen]

Hi @AntonWijbenga,

Those issues with erratic shapes exist in the version implemented here, particularly the circles problem would happen for very complex shapes. In the past I have managed to mitigate it by simplifying the shape with rmapshaper package. I haven't touched this PR in ages (two years) but if there is a version of the polyline offset that solves it you should be able to include it in the appropriate folder in inst/htmlwodgets/lib/ to make it work.

[ainefairbrother]

Hi, thanks for implementing this feature! I would really like to use it, but can't find any documentation regarding how to implement this. Could you please provide a gist?

Thanks again, Aine

[fermumen]

Hi, thanks for implementing this feature! I would really like to use it, but can't find any documentation regarding how to implement this. Could you please provide a gist?

Thanks again, Aine

Hi!

This was never merged to the main branch, and it was implemented a while ago. Not sure how easy it would be to make it work but try remotes::install_github("rstudio/leaflet#614") and perhaps use a CRAN mirror for Early 2020, you can look at the example in scripts from this PR. Alternatively if you can switch to python, the Folium team has this implemented here