[R-sig-Geo] Adding a scale bar and north arrow to a ggplot
Hadley Wickham
hadley at rice.edu
Wed Dec 15 22:20:42 CET 2010
This is something that I hope the student would explore over summer.
Hadley
On Wed, Dec 15, 2010 at 2:27 PM, Pierre Roudier
<pierre.roudier at gmail.com> wrote:
> I'd love to see a separate, dedicated package bringing spatial
> functionalities to ggplot2 - this is such a great tool. However, it
> seems to me that a significant problem when using ggplot2 is the lack
> of geom dedicated to raster data.
>
> My experience is you can't really deal with big rasters using
> geom_tile, it takes too much memory. I guess the development of a
> geom_raster is necessary to fully mimic spplot() functionalities - no
> idea how demanding an effort would that be.
>
> Pierre
>
> 2010/12/15 Roger Bivand <Roger.Bivand at nhh.no>:
>> On Wed, 15 Dec 2010, Paul Hiemstra wrote:
>>
>>> Hi people,
>>>
>>> I posted a similar question to the ggplot2 mailing list and with their
>>> help and a lot of tinkering I got a well working function to add a scalebar
>>> to a ggplot plot. I could add the function to automap, but is there another
>>> package which would be more appropraite, e.g. sp (Roger?)?
>>
>> Paul,
>>
>> If it was added to sp, sp would depend on ggplot2 and its dependencies,
>> which are quite extensive, and include a circularity, because ggplot2
>> suggests maptools, which in turn depends on sp. Consequently, sp is not a
>> good idea. It might even make sense to split sp into sp with just classes
>> and methods, and spViz for vizualisation methods, but changing things now is
>> a bit late!
>>
>> It will be cleaner to try to establish the mapping functionality that uses
>> ggplot2 and sp as a separate package. Maybe Hadley would see this as a
>> sensible development. There are already two supplements to ggplot2 on
>> R-forge, but both moribund, I think, which suggests that this needs thinking
>> through.
>>
>> Roger
>>
>>>
>>> cheers,
>>> Paul
>>>
>>> ps: new version of code here:
>>>
>>> makeNiceNumber = function(num, num.pretty = 1) {
>>> # Rounding provided by code from Maarten Plieger
>>> return((round(num/10^(round(log10(num))-1))*(10^(round(log10(num))-1))))
>>> }
>>>
>>> createBoxPolygon = function(llcorner, width, height) {
>>> relativeCoords = data.frame(c(0, 0, width, width, 0), c(0, height,
>>> height, 0, 0))
>>> names(relativeCoords) = names(llcorner)
>>> return(t(apply(relativeCoords, 1, function(x) llcorner + x)))
>>> }
>>>
>>> addScaleBar = function(ggplot_obj, spatial_obj, attribute, addParams =
>>> list()) {
>>> addParamsDefaults = list(noBins = 5, xname = "x", yname = "y", unit =
>>> "m", placement = "bottomright",
>>> sbLengthPct = 0.3, sbHeightvsWidth = 1/14)
>>> addParams = modifyList(addParamsDefaults, addParams)
>>>
>>> range_x = max(spatial_obj[[addParams[["xname"]]]]) -
>>> min(spatial_obj[[addParams[["xname"]]]])
>>> range_y = max(spatial_obj[[addParams[["yname"]]]]) -
>>> min(spatial_obj[[addParams[["yname"]]]])
>>> lengthScalebar = addParams[["sbLengthPct"]] * range_x
>>> ## OPTION: use pretty() instead
>>> widthBin = makeNiceNumber(lengthScalebar / addParams[["noBins"]])
>>> heightBin = lengthScalebar * addParams[["sbHeightvsWidth"]]
>>> lowerLeftCornerScaleBar = c(x = max(spatial_obj[[addParams[["xname"]]]])
>>> - (widthBin * addParams[["noBins"]]),
>>> y = min(spatial_obj[[addParams[["yname"]]]]))
>>>
>>> scaleBarPolygon = do.call("rbind", lapply(0:(addParams[["noBins"]] - 1),
>>> function(n) {
>>> dum = data.frame(createBoxPolygon(lowerLeftCornerScaleBar + c((n *
>>> widthBin), 0), widthBin, heightBin))
>>> if(!(n + 1) %% 2 == 0) dum$cat = "odd" else dum$cat = "even"
>>> return(dum)
>>> }))
>>> scaleBarPolygon[[attribute]] = min(spatial_obj[[attribute]])
>>> textScaleBar = data.frame(x =
>>> lowerLeftCornerScaleBar[[addParams[["xname"]]]] +
>>> (c(0:(addParams[["noBins"]])) * widthBin),
>>> y =
>>> lowerLeftCornerScaleBar[[addParams[["yname"]]]],
>>> label = as.character(0:(addParams[["noBins"]]) *
>>> widthBin))
>>> textScaleBar[[attribute]] = min(spatial_obj[[attribute]])
>>>
>>> return(ggplot_obj +
>>> geom_polygon(data = subset(scaleBarPolygon, cat == "odd"), fill =
>>> "black", color = "black", legend = FALSE) +
>>> geom_polygon(data = subset(scaleBarPolygon, cat == "even"), fill =
>>> "white", color = "black", legend = FALSE) +
>>> geom_text(aes(label = label), color = "black", size = 6, data =
>>> textScaleBar, hjust = 0.5, vjust = 1.2, legend = FALSE))
>>> }
>>>
>>> library(ggplot2)
>>> library(sp)
>>>
>>> data(meuse)
>>> data(meuse.grid)
>>> ggobj = ggplot(aes(x = x, y = y, color = zinc), data = meuse) +
>>> geom_point()
>>> # Make sure to increase the graphic device a bit
>>> addScaleBar(ggobj, meuse, "zinc", addParams = list(noBins = 5))
>>>
>>>
>>> On 11/18/2010 09:12 PM, Paul Hiemstra wrote:
>>>>
>>>> Dear list,
>>>>
>>>> A common addition to any spatial plot are a north arrow and a scale bar.
>>>> I've searched online for a straightforward way to add those to a ggplot
>>>> plot. I then decided to give a go myself. A crude first attempt for an
>>>> automatic scalebar addition function is listed below. The example works for
>>>> the meuse dataset, but a second with a different dataset did yield good
>>>> results.
>>>>
>>>> My question to you is: is there anyone who has some good tips / example
>>>> code to add a north arrow and a scalebar to a ggplot image. Any expansions
>>>> on the code below are also welcome.
>>>>
>>>> cheers,
>>>> Paul
>>>>
>>>> ps Some info on my system is listed at the very bottom
>>>>
>>>> library(sp)
>>>> library(ggplot2)
>>>>
>>>> data(meuse)
>>>> data(meuse.grid)
>>>>
>>>> string.length = function(s) {
>>>> # browser()
>>>> if(!is.character(s)) s = as.character(s)
>>>> length(strsplit(s, "")[[1]])
>>>> }
>>>>
>>>> makeNiceNumber = function(num, num.pretty = 1) {
>>>> noNumbers = string.length(as.character(round(num)))
>>>> return(round(num / 10^(noNumbers - num.pretty)) * 10^(noNumbers -
>>>> num.pretty))
>>>> }
>>>>
>>>> makeScaleBar = function(obj, plotname, xname = "x", yname = "y", unit =
>>>> "m", placement = "bottomright") {
>>>> # browser()
>>>> range_x = max(obj[[xname]]) - min(obj[[xname]])
>>>> range_y = max(obj[[yname]]) - min(obj[[yname]])
>>>> if(placement == "bottomright") {
>>>> xcoor.max = makeNiceNumber(max(obj[[xname]]) - (0.05 *range_x ),
>>>> string.length(round(max(obj[[xname]]))) - string.length(round(0.3 *
>>>> range_x)))
>>>> xcoor.min = makeNiceNumber(max(obj[[xname]]) - (0.5 *range_x ),
>>>> string.length(round(max(obj[[xname]]))) - string.length(round(0.3 *
>>>> range_x)))
>>>> ycoor = min(obj[[yname]]) + (0.05 * range_y)
>>>> } else {
>>>> xcoor.min = makeNiceNumber(max(obj[[xname]]) - (0.95 *range_x ),
>>>> string.length(round(max(obj[[xname]]))) - string.length(round(0.3 *
>>>> range_x)))
>>>> xcoor.max = makeNiceNumber(max(obj[[xname]]) - (0.5 *range_x ),
>>>> string.length(round(max(obj[[xname]]))) - string.length(round(0.3 *
>>>> range_x)))
>>>> ycoor = min(obj[[yname]]) + (0.95 * range_y)
>>>> }
>>>> scalebar.data = data.frame(x = c(xcoor.max, xcoor.min), y = ycoor, lbl =
>>>> c(paste(xcoor.max - xcoor.min, unit), 0))
>>>> scalebar.data[[plotname]] = min(obj[[plotname]])
>>>> return(list(geom_path(aes(x = x, y = y), data = scalebar.data, lwd = 2,
>>>> color = "black"),
>>>> geom_text(aes(x = x, y = y, label = lbl), data = scalebar.data,
>>>> vjust = 1.3)))
>>>> }
>>>>
>>>> sb = makeScaleBar(meuse.grid, "dist", placement = "topright")
>>>> ggplot(aes(x = x, y = y, fill = dist), data = meuse.grid) + geom_tile()
>>>> + sb[[1]] + sb[[2]]
>>>>
>>>> R version 2.12.0 (2010-10-15)
>>>> Platform: i486-pc-linux-gnu (32-bit)
>>>>
>>>> locale:
>>>> [1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C
>>>> [3] LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8
>>>> [5] LC_MONETARY=C LC_MESSAGES=en_US.UTF-8
>>>> [7] LC_PAPER=en_US.UTF-8 LC_NAME=C
>>>> [9] LC_ADDRESS=C LC_TELEPHONE=C
>>>> [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
>>>>
>>>> attached base packages:
>>>> [1] grid stats graphics grDevices utils datasets methods
>>>> [8] base
>>>>
>>>> other attached packages:
>>>> [1] ggplot2_0.8.7 digest_0.4.2 reshape_0.8.3 plyr_0.1.9 proto_0.3-8
>>>> [6] sp_0.9-62
>>>>
>>>> loaded via a namespace (and not attached):
>>>> [1] lattice_0.19-13
>>>>
>>>> hiemstra at fg-113:~$ uname -a
>>>> Linux fg-113 2.6.32-21-generic #32-Ubuntu SMP Fri Apr 16 08:10:02 UTC
>>>> 2010 i686 GNU/Linux
>>>>
>>>
>>>
>>>
>>
>> --
>> Roger Bivand
>> Economic Geography Section, Department of Economics, Norwegian School of
>> Economics and Business Administration, Helleveien 30, N-5045 Bergen,
>> Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
>> e-mail: Roger.Bivand at nhh.no
>>
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>
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--
Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University
http://had.co.nz/
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