CRGS Coordinate System Definition

The following parameters can be used to define the Cleveland Regional Geodetic Survey coordinate system. Two methods have been tested, and both are presented here. The examples shown primarily use MapInfo Professional's method for defining the coordinate system. An Arc/Info user has donated a "project file". In either case, a generic description of the parameters is also given.

The first method, The "McFadden Shift", was developed first, and is less accurate than the second. The second method is a "Stereographic" projection, which was based on the first, but with some additional parameters that improve the accuracy.

Method I: The McFadden Shift:
The so called "McFadden Shift" method is named for a former staff member of the Cuyahoga County Engineer's Office. Those parameters and methods are described in a series of reports produced by the Engineer's Office from the 1930's to the 1950's.

In previous attempts to define a working "projection" for CRGS, it was observed that the McFadden method resulted in errors of up to 4 feet at the corners of the county. Consistent with those findings, this implementation of the method has shown errors of up to 7 feet at the northeastern edges of the county. At the "center" of the county (intersection of Brookpark and Ridge Roads), the projection is within 1 foot. These measurements are based on an ad hoc review using several points from the City of Cleveland's GPS surveys from the early 1990's, located throughout the county.

In practice, the MapInfo implementation of the McFadden Shift is a modification of the "Ohio State Plane, Northern Zone (1927)" coordinate system, as defined in MapInfo's projection definition file: "Mapinfow.prj". The "CRGS" definition would appear as follows in the file (parameters all on one line following the title):

"--- CRGS ---"
"CRGS-Modified State Plane Ohio 3401, Northern Zone (1927)\p32022", 3, 62, 8, -81.73458, 41.41859, 40.4333333333, 41.7, 75000,60000

The parameters are:

Note: Previously, the Origin Latitude/Longitude values were reversed. The above values are correct.

We recently received an Arc/Info version of the projection from Joe Gautsch of CH2M Hill of Santa Ana, California (consultants to the Northeast Ohio Regional Sewer District). According to Mr. Hill, the Arc/Info "Project" file would look like the following:

output	
projection
lambert	
units feet	
datum nad27	
parameters	
  40.433333     1st Standard Parallel
       41.7     2nd Standard Parallel 
  -81.73458     Central Meridian
   41.41859     Origin Latitude
      22860     False Easting (in meters)
      18288     False Northing (in meters)
end	

Method II: The Stereographic Projection:
The Stereographic Projection is essentially the same as the above "shift" method, but offers a "Scale Factor" to adjust for errors that are magnified toward the edges of the County. Also, some of the other parameters were adjusted to improve performance, particularly for converting CRGS to Ohio State Plane (NAD 83).

The stereographic method was tested against the same GPS control points and showed much better accuracies in general. 50% of all projected points were within 1 foot, and 91% were within 2 feet.

The MapInfo Projection file entry would be as follows:
"--- CRGS ---"
"CRGS - Stereographic Projection for NAD83 State Plane Input", 20, 62, 8, -81.73458, 41.41859, 1.00005,75001,60000.8

The parameters are:

We have not received Arc/Info or Arcview parameters for the stereographic projection, but welcome any contributions.

We are still investigating other methods, and would appreciate any comments. If you have any questions or comments, please e-mail Daniel Meaney, GIS Manager with the Cuyahoga County Planning Commission, or call (216) 443-3700.

November 16, 1999