GeoRegions.jl

Extraction of gridded geoscience/climate data
Author JuliaClimate
Popularity
1 Star
Updated Last
1 Year Ago
Started In
February 2020

GeoRegions.jl

Repo Status Travis CI Documentation Build
MIT License MIT License Latest Documentation Latest Documentation

Created By: Nathanael Wong (nathanaelwong@fas.harvard.edu)

Introduction

GeoRegions.jl is a Julia package that aims to streamline the following processes:

  • query if a point / grid is within a specified boundary
  • extract point data (given coordinates) from a given region
  • extract gridded data (given grid boundaries) from a larger (parent) region (grid must be entirely within the parent region)

In general, these boundaries can be specified either using [N,S,E,W] coordinates, or by longitude and latitude vectors.

GeoRegions.jl can be installed via

] add GeoRegions

Workflow

Is Point/Grid in (Region)?

Relevant Functions: ispointinregion, isgridinregion

Let us define a (Region) domain specified by [rN,rS,rE,rW], with rlon and rlat being the longitude and latitude vectors of the region.
Given that we have a point coordinate (plon,plat), and grid boundaries defined by [N,S,E,W],

We can check if the point is within the region via:

ispointinregion(plon,plat,rlon,rlat)
ispointinregion([plon,plat],rlon,rlat)
ispointinregion(plon,plat,[rN,rS,rE,rW])
ispointinregion([plon,plat],[rN,rS,rE,rW])

And we can check if the grid is within the region via:

isgridinregion([N,S,E,W],rlon,rlat)
isgridinregion([N,S,E,W],[rN,rS,rE,rW])

Extract Point/Grid Data from Parent (Region)

Relevant Functions: regionextractpoint, regionextractgrid, regionextractgrid!

If we have a set of gridded data rdata in a (Region) domain with rlon and rlat being the longitude and latitude vectors defining the region, then given that we have a point coordinate (plon,plat), and grid boundaries defined by [N,S,E,W],

We can extract the data nearest the coordinate (plon,plat) via:

regionextractpoint(rdata,plon,plat,rlon,rlat)

We can extract gridded data for a region bounded by [N,S,E,W] via:

regionextractgrid(rdata,[N,S,E,W],rlon,rlat)

GeoRegions

GeoRegions.jl also utilizes the concept of a GeoRegion (short for Geographical Region), which is simply a set of predefined rectilinear regions specified by [N,S,E,W] coordinates. This is similar to the Python module regionmasks (see https://github.com/mathause/regionmask), which has also inspired many of the functionalities found in GeoRegions.jl.

In GeoRegions.jl, a set of GeoRegions have already been specified in gregiontemplate.txt in the src folder. These include:

  • A global region GLB encompassing the entire globe
  • Giorgi Regions (from Giorgi and Franciso [2000]), specified by GF_xxx, where xxx is a region in Giorgi and Franciso [2000]

Currently, all GeoRegions are rectilinear in the (lon,lat) domain. However, future releases of GeoRegions.jl aim to be more flexible in their specification of region boundaries, allowing for arbitrary polygons as defined in GeometryTypes.jl and PolygonOps.jl

Setup / gregioncopy()

Upon running any function from GeoRegions.jl involving the usage of GeoRegions, unless an array containing GeoRegion information is included as input, the function gregioncopy() is called. gregioncopy() does several things:

  • gregioncopy() checks for a file named gregions.txt in jfol = $(DEPOT_PATH[1])/files/GeoRegions/
  • if $(jfol)/gregions.txt does not exist, gregioncopy() will
    • create the directory jfol (if it does not already exist)
    • copy the information from src/gregionstemplate.txt into $(jfol)/gregions.txt
  • NB: If you want to reset gregions.txt to the default GeoRegions template, gregioncopy(overwrite=true) will overwrite gregions.txt if it already exists

Query for GeoRegion Information

  • gregioninfoall() displays all the available GeoRegions in gregions.txt and their properties in a table format
  • isgeoregion(ID) checks if $(ID) is a valid GeoRegion identifier in gregions.txt

Adding Custom GeoRegions

You can add your own custom GeoRegions to gregions.txt using the function gregioninfoadd(). There are two methods to accomplish this:

  • You can create a textfile in the same format as gregions.txt (e.g. $(path)/addgreg.txt), and point gregioninfoadd() to this textfile, so for example
    • gregioninfoadd("$(path)/addgreg.txt")
  • Or if you want to add in individual GeoRegions manually, you can do it as follows, for example:
    • gregioninfoadd(ID="TST",parent="GLB",N=30,S=25,W=5,E=8,name="Test",throw=false,note="Test")
    • will add the line TST,GLB,30,5,25,8,Test,Test to gregions.txt

Extracting data for GeoRegion

Suppose we are given gridded data rdata spanning longitude rlon and latitude rlat, we extract data for a GeoRegion greg via the following steps:

  1. gregiongridvec(greg,rlon,rlat) returns a Dict (let's call it rinfo) containing necessary information required for extraction of data from rdata
  2. regionextractgrid(rdata,rinfo) will return the data gdata for the GeoRegion greg

Therefore we can call regionextractgrid() multiple times in loops for the same region greg without needing to reextract region information, thus saving time. This is particularly useful when dealing with data over many timesteps.