5

I have this projection in PROJ4:

+proj=tmerc +lat_0=41.836944 +lon_0=-87.684722 +x_0=0 +y_0=0 +datum=NAD83 +units=m +no_defs

What's the WKT translation?

I saw this site: http://cfconventions.org/wkt-proj-4.html but that doesn't help if you don't know the underlying syntax. For me, it's like being given the definition of 5 Chinese words and being told to construct a sentence out of them.

  • I've never seen it, and I'm pretty sure it's not in the EPSG registry. It's not State Plane or UTM, not set right for an Illinois state system. It could be a Chicago ProjCRS, but I didn't find anything on a quick search. – mkennedy Dec 20 '16 at 0:21
  • Using GDAL, you can put the string in a text file, and run gdalsrsinfo on that file to get a WKT string. – AndreJ Dec 20 '16 at 10:15
6

Technically, I think you have two questions. The first is just what's the WKT for this PROJ.4 string. The second is about how a CRS WKT is structured. An answer to the second question is probably too long for Stackexchange, but I've put some pointers below.

In answer to the first (should be single line, formatted into multiple lines for readability), I'm using a modified EPSG / Esri version.

PROJCS["Ben Cooper unknown CRS",
GEOGCS["NAD83",
  DATUM["North American Datum 1983",
    SPHEROID["GRS 1980",6378137.0,298.257222101]],
  PRIMEM["Greenwich",0.0],
  UNIT["Degree",0.0174532925199433]],
PROJECTION["Transverse Mercator"],
PARAMETER["False Easting",0.0],
PARAMETER["False Northing",0.0],
PARAMETER["Scale Factor",1.0],
PARAMETER["Central Meridian",-87.684722],
PARAMETER["Latitude of Origin",41.836944],
UNIT["Metre",1.0]]

Above parameters are what Esri, and generally the version 1 of WKT, use. The EPSG registry uses these parameter names instead:

PARAMETER["Latitude of natural origin",41.836944]
PARAMETER["Longitude of natural origin",-87.684722]
PARAMETER["Scale factor at natural origin",1.0]

So, you can get WKT versions of all the CRS and transformations in the EPSG registry, but they're CRS WKT version 2 which is detailed in ISO and OGC standards released last year. There's some discussion in the annexes about the differences. The website spatialreference.org also has various WKT versions, but doesn't appear to have your particular CRS.

As a starting point on the structure of a CRS WKT string, I suggest you look at the new standard, available from OGC here. That should have references to the earlier WKT versions.

Note: Based on the values of the center parameters when I convert them to DMS, I think they're 41°50'13"N and 87°41'05"W and should probably have their values made more precise when converted to decimal degrees.

  • 1
    If you're interested in how Esri structures our WKT strings, drop me a line (@esri.com). I have some documents that I can send you. – mkennedy Dec 20 '16 at 1:00
  • +1 False easting and northing both set to zero makes me think this is definitely a custom projection. – Mintx Dec 22 '16 at 4:31

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