Add alpha option for hcl.colors pals

[PaulC91]

Salut Timothée!

Based on our discussion about using maptile layers with mapsf, I thought it would be useful to have the alpha argument of hcl.colors accessible via all mf_ functions that have a pal argument, so that palettes can be easily mapped with transparency, retaining some visibility of the tile layer below.

Let me know your thoughts.

Paul

[codecov]

Codecov Report

Merging #14 (10643dd) into master (0574658) will increase coverage by 0.00%.
The diff coverage is 100.00%.

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@@           Coverage Diff           @@
##           master      #14   +/-   ##
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  Coverage   95.42%   95.43%           
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  Files          46       46           
  Lines        2472     2475    +3     
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+ Hits         2359     2362    +3     
  Misses        113      113           

Impacted Files	Coverage Δ
R/mf_map.R	100.00% <ø> (ø)
R/mf_doc_utils.R	100.00% <100.00%> (ø)
R/mf_map_c.R	97.43% <100.00%> (ø)
R/mf_map_pc.R	100.00% <100.00%> (ø)
R/mf_map_pt.R	100.00% <100.00%> (ø)
R/mf_map_s.R	94.82% <100.00%> (ø)
R/mf_map_sc.R	89.70% <100.00%> (ø)
R/mf_map_t.R	98.11% <100.00%> (ø)
R/mf_map_utils.R	98.82% <100.00%> (ø)

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[rCarto]

Hello Paul,

(...) so that palettes can be easily mapped with transparency (...)

The keyword here is easily. I try to keep the number of argument relatively small.
Wouldn't it be enough to use hcl.colors(..., alpha = x) directly in function calls?

library(maptiles)
library(mapsf)
#> Le chargement a nécessité le package : sf
#> Linking to GEOS 3.7.1, GDAL 3.1.2, PROJ 7.1.0
library(raster)
#> Le chargement a nécessité le package : sp
mtq <- mf_get_mtq()
# use EPSG:3857 crs
mtq <- st_transform(mtq, crs = 3857)
# get osm tiles
tiles <- get_tiles(mtq, zoom = 11)
# transform to raster
tiles <- brick(tiles)
# display tiles
mf_theme(mar = c(0,0,0,0), inner = T)
mf_raster(tiles)
mf_map(mtq, "MED", "choro",
      nbreaks = 6, pal = hcl.colors(6, "Blues", alpha = .7),
      add = TRUE, leg_frame = T)
mf_title("Median Income")
mf_credits(txt = get_credit("OpenStreetMap"))
mf_scale(5)

^{Created on 2021-04-22 by the reprex package (v2.0.0)}

[PaulC91]

Hi Timothée,

Thanks for you response!

I did try experiment with this and I realise now I was having issues because I was not setting nbreaks explicitly to match the number of colours I supplied manually. There will be a mismatch between legend colours and choro colours if the default calculated nbreaks is not the same as the number of colours supplied.

library(maptiles)
library(mapsf)
#> Loading required package: sf
#> Linking to GEOS 3.8.1, GDAL 3.1.4, PROJ 6.3.1
mtq <- mf_get_mtq()
mf_theme(mar = c(0,0,0,0), inner = T)
mf_choro(
  # default nbreaks is 6 in this case but if we supply a
  # manual palette with 10 colours there is a mismatch
  mtq, "MED", add = F, leg_frame = T,
  pal = hcl.colors(10, "Blues", alpha = 1, rev = T)
)
mf_title("Median Income")
mf_credits(txt = get_credit("OpenStreetMap"))
mf_scale(5)

^{Created on 2021-04-22 by the reprex package (v1.0.0)}

So the nice benefit of adding the alpha argument for me would be to have the ability to simply supply a palette name and alpha level then have the function calculate the appropriate number of breaks and corresponding colours for me.

But I know it's not too much work to find the default nbreaks number myself and use this when supplying the palette so no worries if you don't want to include! :)

Best,
Paul