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# PyNGL example vector plots

This script shows the different capabilities of drawing vectors on a map. It creates two plots: one global map and one of Northern America.

Software requirements:

• Python 2.7.x
• Numpy 1.9.2
• PyNGL/PyNIO 1.5.0

Run the vector example script:

python PyNGL_vector_rectilinear.py

Script PyNGL_vector_rectilinear.py:

'''
DKRZ PyNGL Script: PyNGL_vector_rectilinear.py

Description:       Python script using PyNGL Python module
- vector plot on map (rectilinear data)
1st plot :  vectors on global map, colored
2nd plot :  vectors colored by temperature
- curly vectors

2015-06-04  meier-fleischer(at)dkrz.de
'''
import numpy, os
import Ngl, Nio

#--  define variables
diri   = "\$HOME/NCL/general/data/new_data/" #-- data directory
fname  = "rectilinear_grid_2D.nc"           #-- data file name

minval =  250.                              #-- minimum contour level
maxval =  315                               #-- maximum contour level
inc    =    5.                              #-- contour level spacing

#--  open file and read variables
f      = Nio.open_file(diri + fname,"r")    #-- open data file
temp   = f.variables["tsurf"][0,::-1,:]     #-- first time step, reverse latitude
u      = f.variables["u10"][0,::-1,:]       #-- first time step, reverse latitude
v      = f.variables["v10"][0,::-1,:]       #-- first time step, reverse latitude
lat    = f.variables["lat"][::-1]           #-- reverse latitudes
lon    = f.variables["lon"][:]              #-- all longitudes

nlon   = len(lon)                           #-- number of longitudes
nlat   = len(lat)                           #-- number of latitudes

#-- open a workstation
wkres           =  Ngl.Resources()          #-- generate an resources object for workstation
wkres.wkWidth   =  1024                     #-- plot resolution 2500 pixel width
wkres.wkHeight  =  1024                     #-- plot resolution 2500 pixel height
wks_type        = "png"                     #-- graphics output type
wks             =  Ngl.open_wks(wks_type,"Py_rectilinear_vector",wkres)

#-- create 1st plot: vectors on global map
res                           =  Ngl.Resources()
res.vfXCStartV                =  float(lon[0])                #-- minimum longitude
res.vfXCEndV                  =  float(lon[len(lon[:])-1])    #-- maximum longitude
res.vfYCStartV                =  float(lat[0])                #-- minimum latitude
res.vfYCEndV                  =  float(lat[len(lat[:])-1])    #-- maximum latitude

res.tiMainString              = "~F25~Wind velocity vectors"  #-- title string
res.tiMainFontHeightF         =  0.024                        #-- decrease title font size

res.mpLimitMode               = "Corners"                     #-- select a sub-region
res.mpLeftCornerLonF          =  float(lon[0])                #-- left longitude value
res.mpRightCornerLonF         =  float(lon[len(lon[:])-1])    #-- right longitude value
res.mpLeftCornerLatF          =  float(lat[0])                #-- left latitude value
res.mpRightCornerLatF         =  float(lat[len(lat[:])-1])    #-- right latitude value

res.mpPerimOn                 =  True                         #-- turn on map perimeter

res.vpXF                      =  0.1                          #-- viewport x-position
res.vpYF                      =  0.92                         #-- viewport y-position
res.vpWidthF                  =  0.75                         #-- viewport width
res.vpHeightF                 =  0.75                         #-- viewport height

res.vcMonoLineArrowColor      =  False                        #-- draw vectors in color
res.vcMinFracLengthF          =   0.33                        #-- increase length of vectors
res.vcMinMagnitudeF           =   0.001                       #-- increase length of vectors
res.vcRefLengthF              =   0.045                       #-- set reference vector length
res.vcRefMagnitudeF           =  20.0                         #-- set reference magnitude value
res.vcLineArrowThicknessF     =   6.0                         #-- make vector lines thicker (default: 1.0)

res.pmLabelBarDisplayMode     = "Always"                      #-- turn on a labelbar
res.lbOrientation             = "Horizontal"                  #-- labelbar orientation
res.lbLabelFontHeightF        =  0.008                        #-- labelbar label font size
res.lbBoxMinorExtentF         =  0.22                         #-- decrease height of labelbar boxes

#-- draw first plot
map1 = Ngl.vector_map(wks,u[::3,::3],v[::3,::3],res)           #-- draw a vector plot

#-- create 2nd plot: sub-region colored by temperature variable
tempa = (temp-273.15)*9.0/5.0+32.0                            #-- convert from Kelvin to Fahrenheit

res.mpLimitMode               = "LatLon"                      #-- change the area of the map
res.mpMinLatF                 =  18.0                         #-- minimum latitude
res.mpMaxLatF                 =  65.0                         #-- maximum latitude
res.mpMinLonF                 = -128.                         #-- minimum longitude
res.mpMaxLonF                 = -58.                          #-- minimum longitude

res.mpFillOn                  =  True                         #-- turn on map fill
res.mpLandFillColor           =  16                           #-- change land color to grey
res.mpOceanFillColor          =  -1                           #-- change color for oceans and inlandwater
res.mpInlandWaterFillColor    =  -1                           #-- set ocean/inlandwater color to transparent
res.mpGridLineDashPattern     =   2                           #-- grid dash pattern
res.mpOutlineBoundarySets     = "GeophysicalAndUSStates"      #-- outline US States

res.vcFillArrowsOn            =  True                         #-- fill the vector arrows
res.vcMonoFillArrowFillColor  =  False                        #-- draw vectors with colors
res.vcFillArrowEdgeColor      =  1                            #-- draw the edges in black
res.vcGlyphStyle              = "CurlyVector"                 #-- draw nice curly vectors
res.vcLineArrowThicknessF     =   5.0                         #-- make vector lines thicker (default: 1.0)

res.tiMainString              = "~F25~Wind velocity vectors"  #-- title string

res.lbTitleString             = "TEMPERATURE (~S~o~N~F)"      #-- labelbar title string
res.lbTitleFontHeightF        =  0.010                        #-- labelbar title font size
res.lbBoxMinorExtentF         =  0.18                         #-- decrease height of labelbar boxes

#-- draw 2nd plot
map2 = Ngl.vector_scalar_map(wks,u[::1,::1],v[::1,::1],tempa[::1,::1],res)

#-- done
Ngl.end()

Plot result:

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