Earth at night

Import NASA's Night on Earth and Reproject in Polar Stereographic

This micro-tutorial requires GRASS 6.5

Get data

Download http://eoimages.gsfc.nasa.gov/ve/1438/land_ocean_ice_lights_2048.tif from NASA's Visible Earth website.

Import

• Create a WGS84 Lat/Lon location (EPSG # 4326)

# import into lat/lon, overriding projection check and
# setting dummy region bounds which fit into geographic
# space (the file is missing georeferencing metadata but
# we do know exactly what it should be).

r.in.gdal -o -l in=land_ocean_ice_lights_8192.tif out=land_ocean_ice_lights

for BAND in red green blue ; do
  r.region map=land_ocean_ice_lights.$BAND n=90 s=-90 w=-180 e=180
done

g.region n=90 s=45 w=-180 e=180

# create 15° and 30° grid line vectors
v.mkgrid map=grid_15 box=15,15 grid=12,24 pos=coor coor=-180,-90 breaks=30
v.mkgrid map=grid_30 box=30,30 grid=6,12 pos=coor coor=-180,-90 breaks=30

Reproject North side

• Create new location based on EPSG #3413

# WGS 84 / NSIDC Sea Ice Polar Stereographic North
<3413> +proj=stere +lat_0=90 +lat_ts=70 +lon_0=-45 +k=1 +x_0=0 \
       +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs  <>

#### NORTHERN HEMISPHERE #################
# pull in grids
v.proj in=grid_15 location=world_ll
v.proj in=grid_30 location=world_ll

g.region n=10000000 s=-10000000 w=-10000000 e=10000000 res=5000 -p

MAP=land_ocean_ice_lights

for BAND in red green blue ; do
  echo "Processing [$BAND] ..."
  r.proj -n in=$MAP.$BAND location=world_ll \
     method=cubic_f memory=300
  r.mapcalc "${MAP}_$BAND = if($MAP.$BAND > 255, 255, if($MAP.$BAND < 0, 0, int($MAP.$BAND)))"
  g.remove "$MAP.$BAND"
  g.rename "${MAP}_$BAND,$MAP.$BAND"
  r.colors $MAP.$BAND color=grey255
  echo
done

# draw
d.erase
d.rgb r=$MAP.red g=$MAP.green b=$MAP.blue
d.vect grid_15 type=boundary color=80:40:40
d.vect grid_30 type=boundary color=120:50:50

# output 
d.out.file night_on_earth_N -c size=1000,1000 format=png
d.out.file night_on_earth_N_small -c size=250,250 format=png

Reproject South side

• Create new location based on the inverse of EPSG #3413

+proj       : stere
+datum      : wgs84
+lat_0      : -90
+lat_ts     : -70
+lon_0      : +135
+k          : 1

#### SOUTHERN HEMISPHERE #################
# pull in grids
v.proj in=grid_15 location=world_ll
v.proj in=grid_30 location=world_ll

g.region n=10000000 s=-10000000 w=-10000000 e=10000000 res=5000 -p

MAP=land_ocean_ice_lights

for BAND in red green blue ; do
  echo "Processing [$BAND] ..."
  r.proj -n in=$MAP.$BAND location=world_ll \
     method=cubic_f memory=600
  r.mapcalc "${MAP}_$BAND = if($MAP.$BAND > 255, 255, if($MAP.$BAND < 0, 0, int($MAP.$BAND)))"
  g.remove "$MAP.$BAND"
  g.rename "${MAP}_$BAND,$MAP.$BAND"
  r.colors $MAP.$BAND color=grey255
  echo
done

# remove stray NULLs
for BAND in  green blue ; do
  echo "Processing [$BAND] ..."
  g.rename "$MAP.$BAND,$MAP.$BAND.tmp1"
  r.neighbors in="$MAP.$BAND.tmp1" out="$MAP.$BAND.tmp2"
  r.patch in="$MAP.$BAND.tmp1,$MAP.$BAND.tmp2" out="$MAP.$BAND"
  g.remove "$MAP.$BAND.tmp1,$MAP.$BAND.tmp2"
  echo
done

# draw
d.erase
d.rgb r=$MAP.red g=$MAP.green b=$MAP.blue
d.vect grid_15 type=boundary color=80:40:40
d.vect grid_30 type=boundary color=120:50:50

# output
d.out.file night_on_earth_S -c size=1000,1000 format=png
d.out.file night_on_earth_S_small -c size=250,250 format=png

Result

• Northern Hemisphere
• Southern Hemisphere