[Gdal-dev] Shapfiles and Projections

[Kent Eschenberg]

Thank you all for your assistance. The gdal/ogr library can read the shapefile 
if the directory also contains the dbf and shx files that came along with the 
shp file. Specific responses below.

  -----Original Message-----
 > gdrinfo doesn't seem to find a projection in a shapefile describiing roads
 > (from the National Atlas). I was expecting something like what gdalinfo
 > finds in a geotiff file. Could someone point me towards the answer?

Martin Chapman wrote:
 > Make sure there is a .prj file with the same name as the .shp file.  NTAD
 > data doesn't always come with these projection files.  If you read the .txt
 > file with the shape file it will tell you what datum it is using.  Attached
 > is a wgs84 prj file that should work if you rename it to be the same as your
 > .shp file.  NTAD is generally in WGS84.

Hmmm ... I didn't do that; there is no prj file but it now seems to work.

Ed McNierney wrote:
 > Unfortunately, the concept of projections and coordinate systems in general
 > was late in coming to the shapefile format, and many (if not most)
 > shapefiles have no projection/coordinate information with them.
 >
 > Your shapefile should have a .txt file with it (presumably roadtrl20.txt
 > if you're using the roads layer from the National Atlas) and it will
 > contain this information:
<clip>

Yes, a txt file was supplied and it has information similar to your example. 
However it doesn't seem to be used. I'm still developing my application and so 
I'll find out soon enough if it is needed by hiding or not hiding the txt file.

Frank Warmerdam wrote:
 > I assume you were using ogrinfo?
 >
 > It will report coordinate system info if it finds it.  Does your shapefile
 > dataset include a .prj file?   If not, there is not declared coordinate
 > system for the file.

Yes, my mistake, I am using ogrinfo. No prj file was supplied but it seems that 
information was provided in the txt file.

Kent
Pittsburgh Supercomputing Center