[R-sig-Geo] Mapping Pacific centered map for Spatial analysis

[Roger Bivand]

On Sun, 13 Mar 2022, Micha Silver wrote:

>
> On 13/03/2022 01:41, sownal chand wrote:
>>  Hello Sir/Madam,
>>
>>  I am Sownal Chand, from Fiji Islands and am currently working on a project
>>  which involves spatial analysis of climate data (Temperature, rainfall,
>>  etc). I have been able to write codes in R for Point interpolations of
>>  these parameters but I require some assistance in mapping these raster
>>  files on the southwest pacific maps. For example, a map of Fiji Islands  (
>>  https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.pinterest.com%2Fpin%2F740982944911004875&data=04%7C01%7CRoger.Bivand%40nhh.no%7C3d492fafcd7247d2090e08da04cde59b%7C33a15b2f849941998d56f20b5aa91af2%7C0%7C0%7C637827580063300234%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=5xNJDee6Glb%2FW7MCkO8biDzHl1%2Bv5hc%2FBsU%2FmO9neLE%3D&reserved=0
>>  ) and I am facing some
>>  difficulties in making these plots.
>>
>>  I hope that some expert would be willing to help me with this and the
>>  map's
>>  CRS setting is a bit confusing and I am a beginner in this area ( i. e,
>>  spatial analysis using R). I have been looking at tutorials and codes to
>
>
> There are tons of online resources. You could, for example, refer to:
>
> https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgeocompr.robinlovelace.net%2F&data=04%7C01%7CRoger.Bivand%40nhh.no%7C3d492fafcd7247d2090e08da04cde59b%7C33a15b2f849941998d56f20b5aa91af2%7C0%7C0%7C637827580063300234%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=08BU9QbKjLNh5TkKeu38etqzU%2FOysx7fqsGoVq3kImw%3D&reserved=0
>
>
>>  crop country boundaries and shapefiles and still found lots of errors in
>>  my
>>  codes.
>
>
> You have raised a few different questions. Would you mind to post what you 
> have done so far, and point out the errors and difficulties?
>

It does also seem possible that the problems are initially caused by using 
geographical (spherical) coordinates rather than projected coordinates. 
Projection of the input points to say EPSG:3460, or for the broader 
Pacific Basin EPSG:3832, may be helpful. See 
https://www.asprs.org/wp-content/uploads/2012/05/10-2000-fiji.pdf for the 
then (publication 2000) valid description of why EPSG only seems to record 
Fiji with 1956 (international ellipsoid) and 1986 (WGS1972 ellipsoid).

EPSG:4326 can be transformed to EPSG:3460 with 2m accuracy. Using then a 
projected planar extent in the local grid, the problem of crossing 180 
degrees is removed. In addition, the interpolation will use metres not 
degrees as the metric of the positions of the points and grid cells. The 
planar representation should also remove plotting problems.

Hope this helps,

Roger

>
>>  Hoping to find solutions to my problems and learn from this.
>>
>>  yours sincerely
>>  sownalc
>>  Contact: sownalchand using gmail.com
>>  PH +679 2960779
>>
>>   [[alternative HTML version deleted]]
>>
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>
>

-- 
Roger Bivand
Emeritus Professor
Department of Economics, Norwegian School of Economics,
Postboks 3490 Ytre Sandviken, 5045 Bergen, Norway.
e-mail: Roger.Bivand using nhh.no
https://orcid.org/0000-0003-2392-6140
https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en