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Linked below is a polygon shapefile whose projection is NAD83 and whose values are LU/LC codes. Coordinates are meters of northing and easting. I would like to convert it to an ASCII raster with coordinates measured in latitude and longitude. I'm sure it is a simple process, but I can't figure out the re-projection. Tools I have are ArcGIS or SAGA or R. I can even open the ASCII text and modify the header if no recalculation is necessary.

http://hawaii.gov/dbedt/gis/lulc.htm

EDIT: Thanks to Dan Patterson for pointing this out: the projection is actually UTM 4, and NAD83 is the DATUM. The output raster should have the same datum. If I want output to have lat/long coordinates, does that mean it has no projection?

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  • Tricky. Is the shape file a regular grid of points in NAD83? Because even if you project those to lat-long you'll not get a regular grid out, so you then have to interpolate to a raster in lat-long. Its def doable in R with packages sp, rgdal, raster,etc... Might get you a full answer later, no GIS capabilities on this phone...
    – Spacedman
    Commented Mar 10, 2011 at 22:53
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    The projection is Universal Trans Mercator, Zone 4 (Meters) its datum is NAD83. You have to define its coordinate system before reprojecting. In ArcGIS, use the Define Projection tool in arctoolbox, then project it
    – user681
    Commented Mar 10, 2011 at 23:00
  • To carry on from the previous comment, you need to define the projection (as stated above), then project it to a Geographic Coordinate System (in ESRI-speak) which is result in decimal degree data, just ensure that you keep the datum the same. These tools are all in the standard arctoolbox toolset.
    – user681
    Commented Mar 10, 2011 at 23:52

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You have two tasks here. The first is to to coordinate transform (re-project) from UTM to Lat/Long (also called geographic or "no projection") and the second to convert from vector to raster.

In arcgis one approach is to use the Project tool to convert to geographic, then use one the To Raster geoprocessing tools located in the Conversion Tools toolbox, in this case Polygon to Raster. And now finally Raster to ASCII tool.

A second and perhaps more intutive vector to raster conversion is to load the shapefile into Arcmap, symbolize the polygons with "categories > unique values" as you want them to look, set the data frame coordinate system to Geographic NAD83 or WGS-1984, and then use File > Export map, save as TIFF with Format>"write geotiff tags" checked, bump the dpi and/or pixel dimensions up as you need them, then follow up with RasterToAscii.

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    Except, you'd want to reproject first, then rasterize second
    – Mike T
    Commented Mar 10, 2011 at 23:24
  • eep! you're right, thanks for catching that. I've changed the order.
    – matt wilkie
    Commented Mar 10, 2011 at 23:36

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