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I have a raster that I downloaded and for whatever reason there is no 'proj4string' when it is read in. 

ndvi= raster("av_TOTND1996v4.bsq")
> proj4string(ndvi)
[1] NA

The documentation says that it is georeferenced, and I am wondering if I could create a custom 'proj4string' to define the data. I also have access to ARCGIS, however I am not really familiar with it, and can't figure out how to reset the center of the projection.

The georefernce information provided is:

Spatial_Reference_Information:
Horizontal_Coordinate_System_Definition:
Planar:
Map_Projection:
Map_Projection_Name: Lambert Azimuthal Equal Area
Lambert_Azimuthal_Equal_Area:
Longitude_of_Projection_Center: -100.000000
Latitude_of_Projection_Center: 45.000000
False_Easting: 0.000000
False_Northing: 0.000000
Planar_Coordinate_Information:
Planar_Coordinate_Encoding_Method: row and column
Coordinate_Representation:
Abscissa_Resolution: 1000.000000
Ordinate_Resolution: 1000.000000
Planar_Distance_Units: meters
Geodetic_Model:
Horizontal_Datum_Name: D_Sphere_ARC_INFO
Ellipsoid_Name: Sphere_ARC_INFO
Semi-major_Axis: 6370997.000000
Denominator_of_Flattening_Ratio: infinity
hrbrmstr
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Reed
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1 Answers1

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Your best bet would be to try and find the code for the data from whoever supplied you the data. Otherwise you will have to construct the proj4 string, assuming you have all the details...

You can search for spatial reference codes on http://spatialreference.org/ so if your data is for a know geographic area you could perhaps search for that location (eg if its a project on Madagascar, maybe it uses a Madagascan grid system).

That site is also a good source of example proj4 strings that might teach you how to construct one from your info. For example, here's a European Lambert Equal Area conical projection that might be a bit like yours:

http://spatialreference.org/ref/epsg/3035/proj4/

Although your centre longitude of -100 tells me its not this (nor is it Madagascar...)

The HTML version of the projection is a bit more enlightening as to what the parameters mean:

http://spatialreference.org/ref/epsg/3035/html/

Note that a proj4string won't define the size of your grid cells. You'll probably have to do that by setting the extent of your grid. Actually I don't see any information about where in your coordinate system the grid cells are. What does extent(ndvi) tell you? Are you sure there's not a companion .hdr file you've not got?

Spacedman
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  • Thanks, that was very helpful and I came up with this: 'proj.ndvi = "+proj=aeqd +lat_0=-100 +lon_0=45 +x_0=1000, +y_0=1000 +units=m"' When I set this, and then check it, it find that the 'ellps' argument defaults to 'WGS84'. ('coord. ref. : +proj=aeqd +lat_0=-100 +lon_0=45 +x_0=1000, +y_0=1000 +units=m +ellps=WGS84'). I'm just curious if this default is correct, or where i can find more information on what it should be since the 'Sphere_ARC_INFO' name specified in the Metadata (above) generates 'unknown elliptical parameter name' error – Reed Mar 01 '15 at 16:57
  • there is a companion .hdr file but I have no clue how to use it, am i missing something when i read in the file? – Reed Mar 01 '15 at 17:30
  • Looks like a sphere of that radius, so try adding a=6370997 and b=6370997. Could you add the output of summary(ndvi) to your Q - it might tell us if its reading in the hdr. If it has the same name as the .bsq and is in the same folder it should be read (but it might not have the projection in it anyway). Actually, I wonder if EPSG:2163 is your projection: http://spatialreference.org/ref/epsg/2163/html/ (found by searching for that sphere radius) – Spacedman Mar 01 '15 at 21:49