[R-sig-Geo] Positing a coord_proj for ggplot2
mdsumner at gmail.com
Wed Jul 29 05:52:18 CEST 2015
On Wed, 29 Jul 2015 at 05:38 Roger Bivand <Roger.Bivand at nhh.no> wrote:
> On Tue, 28 Jul 2015, Hadley Wickham wrote:
> >>> This won't be in ggplot2 right now as Hadley is updating/refactoring
> >>> the package and "coords" are going to work a bit differently. Plus
> >>> this adds a dependency I'm not sure he wants to add to it. You can
> >>> stick it in your own, local copy of ggplot2 and re-collate and rebuild
> >>> to use it.
> >>> proj4::project (and even spTransform, to a certain degree - no pun
> >>> intended) are unhappy dealing with lat/lon values outside the -90/90 :
> >>> -180:180 range and even have some issues with points right at the
> >>> extremes, so I did the following in the linked code:
> >>> df$x <- ifelse(df$x <= -180, -179.999999999, df$x)
> >>> df$x <- ifelse(df$x >= 180, 179.999999999, df$x)
> >>> df$y <- ifelse(df$y <= -90, -89.999999999, df$y)
> >>> df$y <- ifelse(df$y >= 90, 89.999999999, df$y)
> >> This may well be unsafe, as 0 - 360 is also valid for longitudes, and in
> >> many cases -180 - 360 will also be feasible. The test in sp is in
> >> sp:::.ll_sanity() which uses an internal tolerance (which may be set)
> to do
> >> similar checks.
> > Is there a function to do this the "right" way? i.e. cut the
> > antimeridian after rotation?
> Not really, because the changes made are most often heuristics based on
> use cases for places near the antimeridian needing planar plotting. The
> "cleanest" solution is probably to determine either 0 to 360 or -180 to
> 180 for a given prime meridian, and fold back anything out of domain, so
> that it can always be displayed on a sphere. -2 or 26 hours is similar in
> relation to daily time (really 2200 the day before or 0200 the day after).
A question on the proj-devel list would probably elicit a principled
> response; I think for example that New Zealand cartographers have a lot of
> experience that many others (US, Europe) do not have.
And Antarcticians. It's surprising how much of a pain this is in many
different ways. The authoritative solution is by Mike Bostock of course.
future? GIS just doesn't traditionally give this sort of flexibility.
> > Hadley
> Roger Bivand
> Department of Economics, Norwegian School of Economics,
> Helleveien 30, N-5045 Bergen, Norway.
> voice: +47 55 95 93 55; fax +47 55 95 91 00
> e-mail: Roger.Bivand at nhh.no
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