[GRASS-user] reprojection problem

Tyler Smith tyler.smith at mail.mcgill.ca
Thu Dec 15 12:11:40 EST 2011


I'm a GIS novice, trying to reproject a vector layer. My objective is to
get a world map
projected into Lambert Equal-Area, centered on the north pole. I chose this
as it shows the entire arctic well, but I don't have to use Lambert

This is what I've tried so far:

Created a new location with the location wizard, selecting
 'read projection and datum terms from georeferenced data file'

The target file was:

retrieved  from http://www.sharegeo.ac.uk/handle/10672/124

This appears to be correct, as I now have my location world-ll, which
contains in the
PERMANENT mapset the layer WorldCountries. The region info is:

projection: 3 (Latitude-Longitude)
zone:       0
datum:      wgs84
ellipsoid:  wgs84
north:      83:37:38.7084N
south:      90S
west:       180W
east:       180E
nsres:      8:40:52.93542
ewres:      18
rows:       20
cols:       20
cells:      400

I then made a new location, using the wizard again:
  select coordinate system from a list: laea
  central parallel: 90
  central meridian: 100
  false northing: 0
  false easting: 0
  datum code: wgs84

I then set the extent to 90N, -90S, 180E, -180W, NS resolution 0.1, EW
resolution 0.1

The resulting region info is:

name       : Lambert Azimuthal Equal Area
proj       : laea
datum      : wgs84
ellps      : wgs84
lat_0      : 90
lon_0      : 100
x_0        : 0
y_0        : 0
no_defs    : defined
unit       : meter
units      : meters
meters     : 1

>From here I used the gui to import the WorldCountries vector layer from
generating the command:

  v.proj input=WorldCountries location=world-ll mapset=PERMANENT

This command runs without error, but with a few suspicious warnings:

  v.proj input=WorldCountries location=world-ll mapset=PERMANENT
  Building topology for vector map <WorldCountries>...
  Registering primitives...
  55402 primitives registered
  417249 vertices registered
  Building areas...
  Area of size = 0.0 ignored
  Area of size = 0.0 ignored
  27423 areas built
  26809 isles built
  Attaching islands...
  Attaching centroids...
  Number of nodes: 54788
  Number of primitives: 55402
  Number of points: 0
  Number of lines: 0
  Number of boundaries: 28000
  Number of centroids: 27402
  Number of areas: 27423
  Number of isles: 26809
  Number of incorrect boundaries: 1
  Number of centroids outside area: 1
  Number of areas without centroid: 22

At this point, the WorldCountries layer appears in the Map Layers tab, but
not on the
display. Zooming to selected layer produces an error:
  Unable to zoom to vector map <WorldCountries at PERMANENT>

What have I done wrong?


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