On 8 October 2010 19:52, Barry Rowlingson <b.rowlingson@lancaster.ac.uk>wrote:

> On Fri, Oct 8, 2010 at 5:32 PM, ogbos okike <ogbos.okike@gmail.com> wrote:
>
> > My data points are given in latitude and longitude (geographic). Using
> AACGM
> > geomagnetic coordinate software, I converted them to magnetic
> coordinates.
> > World map (such as implemented in R, which can be generated using maps
> has
> > no data points). It is only implemented in R such that one can use maps
> > library to generate it. However, that is in geographic coordinates.
>
>  I'm not sure what world map you are referring to here. Can you tell
> us the R commands that plot it?
>
> library(maps)
 data(worldMapEnv)
 map("world")
The three steps above in R gives you the world map I mean.


 The data points are in there somewhere,

 Yes. The points are there. Thanks. But I wonder how R use those few data
points to create the map. Transforming them will be easy for me but how to
feed them back to R so as to use map library to generate the world map will
be a problem.
Plotting the transformed coordinates (world) using raster will not make
meaning as it will not appear as map. What I am doing involves using raster
package to plot huge lightning strikes detected over the globe and using
map("world", add = TRUE) to add world map to the raster plots. That works
perfectly well if I leave my data in geographic coordinates.  But since I
wish to know how this behaves in magnetic coordinates, I need to transform
both (i.e. I also need the world map above in magnetic coordinate.

> and if you want to transform
> them with something that isn't spTransform then we'll have to tell you
> how to get them. If the map is a SpatialPolygonsDataFrame then the
> coordinates are obtained by getting the individual polygons which are
> made up of rings which are made up of points and so on. Messy but
> possible to apply a generic transformation function to them.
>
>  What does your conversion software work on? Text files?
>
> Yes
Ogbos

> Barry
>

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