Using the "|" operator, the basemap is not rendered in knitted markdown

[felixhaass]

First off, thanks for the terrific package! It has helped me a lot.

I've stumbled across the following minor bug. When I run mapview(breweries) | mapview(franconia) in an rmarkdown chunk that I subsequently knit to HTML, the basemaps are missing.

Here's the code I've used:

---
title: "Testing Leaflet Sliders"
output: html_document
---

```{r}
library(mapview)
mapview(breweries) 
```


```{r}
library(mapview)
mapview(breweries) | mapview(franconia)
```

This gives me the following output:

When I use mapview(breweries) | mapview(franconia) in RStudio, the Viewer Pane shows the correct basemap.

I'm using mapview version 2.9.4.

I tried to narrow down from where the problem originates, but no success. Any idea?

Thanks,
Felix

[tim-salabim]

Thanks @felixhaass , this is a tough one. No idea why this doesn't work. Doesn't help that we don't see any errors in the browser console... Not sure how to fix this

[trafficonese]

It seems that markdown is having problems with leaflet panes.

The following example will show no basemap in a knitted document, but if you remove options = pathOptions (pane = "right") the basemap appears.
Also, if you give the pane the name tile, it also works, so I guess markdown only looks for basemaps in the leaflet-pane leaflet-tile-pane class.

So I'm not so sure that the problem comes from mapview or leaflet.extras2.

library(leaflet)
leaflet() %>%
  addMapPane("right", zIndex = 0) %>%
  addTiles(group = "base", layerId = "baseid", options = pathOptions(pane = "right"))

[tim-salabim]

@trafficonese great catch! Any ideas how to resolve this? Sounds like a job for rstudio & leaflet...

[trafficonese]

Unfortunately, I don't really have a lot of experience with markdown and the entire processing pipeline to figure out where this error actually shows up. But I'm going to dig into rmarkdown a bit, maybe I can find out something.

[tim-salabim]

Well, I'd say that given that you've isolated the problem to be either leaflet or rmarkdown based, we should consider opening an issue with rstudio (probably leaflet).

FWIW, this works

library(leaflet)
leaflet() %>%
  addMapPane("tile", zIndex = 0) %>%
  addTiles(group = "base", layerId = "baseid", options = tileOptions(pane = "tile"))

whereas this doesn't

library(leaflet)
leaflet() %>%
  addMapPane("right", zIndex = 0) %>%
  addTiles(group = "base", layerId = "baseid", options = tileOptions(pane = "right"))

I used tileOptions instead of pathOptions as I think it's better suited for addTiles

[cderv]

FWIW I looked a bit into that as you opened an issue in rmarkdown. I believe this is something missingin Leaflet JS library.
See rstudio/rmarkdown#1949 (comment)

Not sure what could be done on our side, but if something, I would say it would be in leaflet R package by patching the CSS.

[cderv]

We've decided to add the missing CSS in leaflet. Hopefully this is enough to help with your issue.

See rstudio/leaflet#770

[tim-salabim]

Should work now with the dev version of leaflet rstudio/leaflet#770