Raster legend not updated if specifying manual breaks

[lbusett]

Hi,

on current mapview@develop, the raster legend is apparently not properly updated when manually specifying breaks. For example:

library(raster)
library(mapview)
f <- system.file("external/test.grd", package="raster")
r <- raster(f)
pal <- grDevices::colorRampPalette(RColorBrewer::brewer.pal(5, "RdYlGn"))
mapview(r, col.regions= pal)

gives:

, but if we manually specify breaks, the map is modified, but the legend is no longer "correct":

brks <- classInt::classIntervals(1:10000,
                                 style = "fixed",
                                 fixedBreaks = seq(0,10000,500),
                                 intervalClosure = "right")
mapview(r, col.regions= pal, at = brks$brks)

I may be wrong, but I think previous mapview behaviour was different, and the legend followed the specified "breaks". Am I wrong?

HTH,

Lorenzo

[lbusett]

UPDATE

I tried to see if I was able to "fix" this but without success... sorry. FYI: if it helps, I saw that "old" behaviour can be "restored" easily by uncommenting here.

mapview/R/raster.R

Line 164 in 0a3517f

# m = addRasterLegend(x = x,

[tim-salabim]

I know, legends are the hill I'm gonna die on... I'll have a look at this on the weekend.

[lbusett]

Thanks... and sorry for the bad news. I tried to work on this but failed.
By the way: I just noticed that also the behaviour you get by reinstating addRasterLegend does not appear to be correct, unless you set a small number of breaks (e.g., 10), leading to a "discrete" legend instead of a colourbar.

[lbusett]

Oh, sorry: With low number of breaks, also current mapview is ok:

f <- system.file("external/test.grd", package="raster")
r <- raster(f)
pal <- grDevices::colorRampPalette(RColorBrewer::brewer.pal(5, "RdYlGn"))
brks <- classInt::classIntervals(1:10000,
                                 style = "fixed",
                                 fixedBreaks = seq(0,10000,1000),
                                 intervalClosure = "right")
mapview(r, col.regions= pal, at = brks$brks)

[tim-salabim]

Sorry for the long silence. I think this is a deliberate choice of mine (though the exact reasons escape me as it is long ago I made the decision). IIRC, I read somewhere that the human brain can perceptually not distinguish meaningfully between more than ~12 shades of a colour. That's why we map to a continuous legend when there are more than 12 (maybe 11) breaks. Also, not restricting this means that the legend can become quite useless if too many breaks are specified (as the bottom of the legend will disappear from the window).

Therefore, I am a bit reserved about changing this behaviour. After all, mapview is intended for quick views/checks of the data. If someone needs a different legend, they can easily omit it in the mapview call and add it explicitly using leaflet::addLegend.

What do you think @lbusett ?

[lbusett]

@tim-salabim

having a discrete legend when the number of breaks is low and a continuos one when it is high seems fine to me.

My main concern here was that when specifying a high number of breaks (to get a continuous legend), the legend is no longer correct: the raster is shown using the correct "colors" based on the breaks, while the legend shows the values we would get if breaks were not set.
My use-case for that is to be able to specify a legend/palette with fixed range irrespective of a raster "real" values. Maybe there is a easier way to set min-max to achieve this?

[tim-salabim]

The above commit should at least partly solve this issue. Not sure if we should limit the breaks to the range of the data or simply go with what the user specifies. Thoughts?

[lbusett]

@tim-salabim

thanks, Iìll try to check it out tomorrow. In my opinion it would be better to go with what the user specifies (that's what's already happening with the discrete legend, apparently). That would allow for example to use colors to reflect "absolute" values of a variable within a specified range rather than its "relative" variations within the extent. If I am not mistaken , limiting the breaks to the range of data would more or less mimic what already happens if breaks are not specified (i.e., first figure in my first post).

[tim-salabim]

Ok, I think I now (sort of) understand what's going on... pal = leaflet::colorNumeric(...) in conjunction with leaflet::addLegend(..., pal = ...) seems to only evaluate the palette until the maximum of the domain, hence neglecting all values beyond its max value. Therefore, I opted to always use leaflet::colorBin when specifying breaks (at), i.e. remove the distinction between < or > than 12 distinct color values.

This now gives for your example above:

library(raster)
library(mapview)

f <- system.file("external/test.grd", package="raster")
r <- raster(f)
pal <- grDevices::colorRampPalette(RColorBrewer::brewer.pal(5, "RdYlGn"))
mapview(r, col.regions= pal)

brks <- classInt::classIntervals(1:10000,
                                 style = "fixed",
                                 fixedBreaks = seq(0,10000,500),
                                 intervalClosure = "right")

mapview(r, col.regions= pal, at = brks$brks)

which seems correct.

Let's see what will come up in other use-cases. This whole legend thing really seems to go round and round. Fixing something here, likely means breaking something somewhere else... Sigh. Though, at least I feel it's headed in the right direction.

[lbusett]

@tim-salabim

Hi, I was finally testing this out, but i have a problem: After updating my "develop" fork , trying to do devtools::load_all() yields:

Loading mapview Error in setMethod("plainView", signature(x = "RasterLayer"), function(x, : no existing definition for function ‘plainView’

Am I doing something wrong?

Lorenzo

[tim-salabim]

I never use devtools::load_all(), I just build the package (ctrl + shift + b in RStudio). Never seen this error before

[lbusett]

Ok, I'll try again. It's just that i did not want to mess with my currently installed mapview version.

[lbusett]

Ok, I managed to have it working (just by loading "plainview" beforehand.

Now the example with fixed breaks works ok (thanks). However, unfortunately now I a m seeing this if I do not specify the breaks:

library(raster)
library(mapview)
f <- system.file("external/test.grd", package="raster")
r <- raster(f)
mapview(r)

Below, my session info:

• Session info ------------------------------------------------------------------------------------------------------------------
  setting value
  version R version 3.6.3 (2020-02-29)
  os Windows 10 x64
  system x86_64, mingw32
  ui RStudio
  language (EN)
  collate English_United Kingdom.1252
  ctype English_United Kingdom.1252
  tz Europe/Paris
  date 2020-07-02

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