working with the wisconsin county coordinate systems (wccs) a.j. wortley, jay yearwood

Working with the Wisconsin County Coordinate

Systems (WCCS)

A.J. Wortley, Jay Yearwood

EWUG 2005 - Working with the County Coordinate Systems

Wisconsin County Coordinate Systems

Who is using the County Coordinate Systems?

Who is confident that their data is defined correctly?


What are the Wisconsin County Coordinate

Systems?

Individual counties began developing their own coordinate systems in the 1980s to support large-scale local mapping

Designed to minimize ground-to-projected-grid differentials

WisDOT contracted for development of county-based coordinate systems in 1993


More on the Wisconsin County Coordinate Systems (WCCS)

Based on a mathematical technique that modifies the underlying GRS80 spheroid for each county

Documented in “Wisconsin Coordinate Systems” handbook published by State Cartographer’s Office


Why Project Data to or from WCCS?

Not necessarily a problem if you always work inside a particular county

May be an issue if you are trying to use GIS data from more than one county

Locally-produced data is becoming more widely available and need to be integrated on a regional or statewide basis


How is Projecting Data to or from WCCS a

Problem?

GIS users often expect projection of WCCS-referenced data to be quick and easy

Most GIS software lack tools that handle WCCS projection in a reliable & straightforward manner

Little or no documentation of best practices exists


How is Projecting Data to or from WCCS a Problem? (continued)

Finding a method for projecting WCCS-referenced data can be time-consuming & frustrating

Users (including consultants AND software) can easily define or project WCCS data incorrectly, resulting in positional offsets


Defining Terms Used in Projecting Data

First, a few caveats…– This is not a complete or rigorous discussion of

projection-related issues (not enough time)

– For convenience, we take “Projection” (noun) to be any combination of coordinate system, map projection, and reference datum or spheroid

– For more technical info, refer to “Wisconsin Coordinate Systems” handbook...


Defining Terms Used in Projecting Data (continued)

Projection Definition: Assigning a projection to a spatial data set

Projection Transformation: Physically transforming spatial data from one projection to another projection (“hard” projection)

Projection On-the-Fly: Data stored in different projections are temporarily presented in a single projection for display purposes (“virtual projection”)


How are Projection Functions Handled in

ArcGIS?Projection Definition

ArcGIS version 8– Users must enter WCCS parameters– Problems arise because parameters for both

a custom spheroid and datum are required

ArcGIS version 9– Includes WCCS parameters– Not all WCCS parameters have been tested

and verified



ArcGIS? (continued)

Projection Transformation

Note: Projection of source data must be defined prior to the actual projection!

ArcGIS version 8– Offers users a drop-down list of

transformation methods when using WCCS...



ArcGIS? (continued)Projection Transformation

ArcGIS version 8 - suggested transformation methods:

Best:– Use “Geocentric Translation” with “0” (zero) for

all parametersAlternate:– Use NADCON transformation when going from

NAD27 to WCCS– Use HARN transformation when going from WCCS

to DD, WCCS to NAD83, or NAD83 to WCCS



ArcGIS? (continued)


ArcGIS version 9 - first the bad news…

– No drop-down list of transformation methods when using WCCS

– Transformation must be typed manually from a list of “valid transformation methods”



ArcGIS? (continued)


ArcGIS version 9 - the good news…

– Projection wizard supports projection from WCCS to regional/statewide systems such as WTM83/91

– ...but not the reverse, nor from WCCS to WCCS

– Better news about projection on-the-fly



ArcGIS? (continued)


Workstation ArcInfo

– Has been used successfully for years to project to or from WCCS

– Different organizations use different approaches– Procedures not agreed upon or well documented– Most orgs are migrating to ArcGIS for these

tasks



ArcGIS? (continued)


Verify your projection methodology!

– Always recommended when using new methods– Verify by comparing your projected data to the same

data projected using an established method– Compare to sample test data, or– Compare with sample points projected using WISCON

(point data only)– DON’T rely on results from other CAD/GIS software– Turn off on-the-fly projection



ArcGIS? (continued)

Projection On-the-Fly

ArcGIS version 9

– On-the-fly projection appears to work for vector WCCS data

– On-the-fly projection of raster data from WCCS to regional/statewide systems works...

– ...but not the reverse



ArcGIS? (continued)

Projection On-the-Fly

ArcGIS version 9

– Use with caution!!– All data must first be properly defined– If not, erroneous projection on-the-fly may

result– ...despite the appearance that all is working

fine!


Other Projection Frontiers

to be Explored

Further testing and documentation of projection tools is needed!

Differences in projection functionality between ArcInfo, ArcView & ArcGIS versions 8 or 9 and other software are not well documented

Geodatabase “Spatial Layer Definitions” are not well understood, tested or documented


Wisconsin Land Information Association

WCCS Task Force

Mission: “investigate, analyze, and document…software implementations of data conversions to and from the WCCS”Task Force to make recommendations to simplify these conversionsIncludes representatives from academic, government & private sectorsFor info about the work of the Task Force, see:http://www.geography.wisc.edu/sco/coordsys/

index.php


Wisconsin Land Information Association WCCS Task Force

(cont.)

Based on user frustration and inconsistent software definitions, Task Force recommended the redesign of the WCCS.

Redesign was endorsed by WLIA, WLIB, WSLS, WCSA, LION

Grant obtained for funding of redesign.

Work began Summer 2005

Redesign done, in QC phase


WCCS Redesign

To simplify use of the Wisconsin County Coordinate Systems (WCCS), the WLIA Task Force on Wisconsin Coordinate Systems has recommended their re-design. The re-designed systems are all to be based upon the GRS 80 reference ellipsoid, without the need to change any ellipsoid parameters during coordinate transformations. In addition, coordinate shifts between the original and re-designed systems are to be negligible so that legacy databases can be integrated with new data without concern for positional discrepancies. The target maximum absolute value in any coordinate shift (easting (X) or northing (Y)) is five millimeters.

-A Methodology for Re-Design of the Wisconsin County Coordinate Systems Draft Report


What to Expect?

More complete info at WSLS, WLIA (better timeframe)

Redesign to be complete on April 2006.

Parameters will be submitted to software vendors to be incorporated into next releases.

Regional presentations to be done around the state.

Follow-up presentations at major conferences.


What YOU will need to do

Remember to verify new projection transformation methods AND your data!

– Check the WCCS Task Force website for sample test coordinate data

– Use multiple conversion software for comparison.– Use WISCON (this is not an endorsement)

• Desktop point data projection utility• Developed under contract to WisDOT• May order from private vendor; contact info on SCO site• Cost approximately $200 per copy• Vendor is not known for prompt replies or for support...


What YOU need to do now

Verify your data

Verify your data

Verify your data


Question-and-Answer

working with the wisconsin county coordinate systems (wccs) a.j. wortley, jay yearwood

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