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SEWRPC Technical Report No. 35, Vertical Datum Differences In

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SEWRPC Technical Report No. 35, Vertical Datum Differences In • J... II K' -ITJ::l/..,HE J) t / ~ L ~ I ( ,/ ,• I~ ...... )i' ~ If... 1f -. 'u J • • s.o THEASTERN wiseo - P. LAN 'N,LN G eOMMISS 0'1\1 SOUTHEASTERN WISCONSIN REGIONAL PLANNING COMMISSION KENOSHA COUNTY RACINE COUNTY Leon T. Dreger David B. Falstad, Chairman Thomas J. Gorlinski Martin J. Itzin Sheila M. Siegler Jean M. Jacobson, Secretary MILWAUKEE COUNTY WALWORTH COUNTY Daniel J. Diliberti John D. Ames William Ryan Drew Anthony F. Balestrieri Tyrone P. Dumas Allen L. Morrison, Treasurer OZAUKEE COUNTY WASHINGTON COUNTY Leroy A. Bley Lawrence W. Hillman Thomas H. Buestrin, Daniel S. Schmidt Vice-Chairman Patricia A. Strachota Elroy J. Schreiner WAUKESHA COUNTY Duane H. Bluemke Robert F. Hamilton Paul G. Vrakas SOUTHEASTERN WISCONSIN REGIONAL PLANNING COMMISSION STAFF Kurt W. Bauer, PE, AICP, RLS ........................ Executive Director Philip C. Evenson, AICP ............................. Assistant Director Kenneth R. Yunker, PE ............................. Assistant Director Robert P. Biebel, PE ...................... Chief Environmental Engineer Monica C. Drewniany, AICP ............... Chief Special Projects Planner Leland H. Kreblin, RLS ....................... Chief Planning Illustrator Elizabeth A. Larsen ............................ Administrative Officer Donald R. Martinson, PE .................. Chief Transportation Engineer John R. Meland .................. Chief Economic Development Planner Thomas D. Patterson. .. Geographic Information Systems Manager Bruce P. Rubin ............................... Chief Land Use Planner Roland O. Tonn, AICP .............. Chief Community Assistance Planner TECHNICAL REPORT NUMBER 35 VERTICAL DATUM DIFFERENCES IN SOUTHEASTERN WISCONSIN Prepared by Earl F. Burkholder, PLS, PE Consulting Geodetic Engineer Circleville, Ohio 43113-7240 for the Southeastern Wisconsin Regional Planning Commission December 1995 Inside Region $2.00 Outside Region $5.00 (This page intentionally left blank) SOUTHEASTERN WISCONSIN REGIONAL PLANNIN 916 N. EAST AVENUE • P.O. BOX 1607 • WAUKESHA, WISCONSIN 53187-1607 • December 7,1995 STATEMENT OF THE EXECUTIVE nffiECTOR Since early 1964, the Regional Planning Commission has recommended to the governmental agencies operating within the Southeastern Wisconsin Region the use of a unique system of survey control as a basis for the compilation oflarge-scale topographic and cadastral maps, and as a basis for the conduct of land and engineering surveys. More recently, the Commission has also recommended the use of this system as a basis for the development of automated, parcel-based land information systems within the Region. The recommended survey control system involves the remonumentation of the U. S. Public Land Survey corners within the Region and the establishment of State Plane Coordinates for those corners in order to provide a reliable horizontal survey control network. The system, however, also includes the establishment of elevations for the remonumented corners and for related auxiliary benchmarks to provide a reliable vertical survey control network fully integrated with the horizontal survey control network. As of January 1996, the recommended horizontal and vertical survey control system will have been extended over a total area of 1,840 square miles, or about 68 percent of the approximately 2,700-square-mile Region; and elevations determined for about 8,300 U. S. Public Land Survey System corners and accessories thereto, and for an additional 1,800 benchmarks which are not U. S. Public Land Survey System corners. All of these elevations were determined to meet Federal standards for Second Order Class II differential level networks. All of this vertical survey control work within the Region has been referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29), a datum formerly known as Mean Sea Level Datum. The Federal government in 1977 determined to undertake a readjustment of the national vertical control survey network and to adopt a new datum, known as the North American Vertical Datum of 1988 (NAVD 88). The new vertical survey control datum does not provide any significant advantages over the continued use ofthe old datum within the seven-county Southeastern Wisconsin Region. Indeed, the introduction of the new datum may be expected only to entail unnecessary cost and potential confusion in the use of benchmark elevations. This potential confusion may lead to costly errors in surveys made for public works engineering and construction, and for the exercise ofland use regulations relating particularly to floodlands. In this respect, it should be noted that the differences between the two datums within the Region range from about 0.10 foot to about 0.36 foot, just enough to cause serious problems if neglected in the conduct of engineering surveys, and in the administration offloodland zoning regulations. Since no benefits can be shown as attendant to the very large costs that would be entailed in shifting from NGVD 29 to NA VD 88 within the Region, the Southeastern Wisconsin Regional Planning Commission has determined to continue to utilize NGVD 29 as a basis for its surveying and mapping activities within Southeastern Wisconsin. In order to facilitate the use of the NAVD 88 datum within the Region by such agencies as may desire to do so despite good reasons to the contrary, the Commission in October 1994 entered into an agreement with Mr. Earl F. Burkholder, Consulting Geodetic Engineer, to review existing transformation methodologies, develop as may be necessary new methodologies, and propose recommended methodologies for the ready and reliable bidirectional transformation of elevations between the two vertical datums concerned. The work was completed in December 1995 and the results are presented in this report. The transformation methodolo­ gies herein presented permit the ready conversion of elevations between the two datums concerned to various levels of accuracy, including a level of accuracy adequate to maintain the integrity of the Second Order Class II benchmark elevations within the Region. Respectfully submitted, ~Kurt W. Bauer Executive Director (This page intentionally left blank) EARL F. BURKHOLDER, PLS, PE Consulting Geodetic Engineer P.O. Box 13240 Circleville, Ohio 43113 Tel & Fax (614) 477~6261 December 1, 1995 Dr Kurt Bauer, Executive Director Southeastern Wisconsin Regional Planning Commission P.O. Box 1607 Waukesha, Wisconsin 53187 Dear Dr. Bauer, Transmitted herewith is the report entitled, "Vertical Datum Differences in Southeastern Wisconsin." The report documents the relationship between the National Geodetic Vertical Datum of 1929 (NGVD 29) as presently used throughout the seven-county area served by the Southeastern Wisconsin Regional Planning Commission (SEWRPC) and the North American Vertical Datum of 1988 (NAVD 88) as published by the National Geodetic Survey (NGS) of the National Oceanic Atmospheric Administration (NOAA) of the U.S. Department of Commerce. The Southeastern Wisconsin Regional Planning Commission has, over a period of more than 30 years, established and promoted use of elevations referenced to the NGVD 29 for topographic mapping, for floodplain delineation, for sewerage, drainage, flood control and water quality studies, and for hydrologic and hydraulic computations. The Commission has also maintained a system of closely spaced monumented benchmarks throughout the region as part of the infrastructure which supports public works engineering and site development. The value of the information accumulated in the NGVD 29 database over the past 30 years will be preserved and enhanced by documenting the relationship between the two datums throughout the Region. Three options for determining the relationship between the two datums were identified. The most costly option would be to resurvey all benchmarks within the Region on the new datum. Another option, also costly, would be to abstract all control leveling information from existing records and readjust all control leveling networks. The third option would be to employ an interpolating program known as VERTCON developed for that purpose by the NGS. As a combination of options two and three, this report documents the performance of VERTCON against both the elevations published by the NGS and representative lines of Second-Order leveling completed by the Commission. For the comparatively small number of cases where a First-Order vertical datum trans­ formation is required the resurvey option is recommended. However, elevations for thousands of existing Second- and Third-Order benchmarks scattered throughout the Region can be efficiently converted from one datum to the other using VERTCON as described in the report. The relationship to and use of the International Great Lakes Datum is also described. Thank you for the opportunity to be of service to the Commission. Yours truly, . j ~ /J . ~~~. Earl F. Burkholder, PLS, PE Consulting Geodetic Engineer (This page intentionally left blank) TABLE OF CONTENTS Page Page Introduction and Summary ............. 1 Accuracy Considerations ............... 6 Vertical Datums ...................... 2 Iso-Hypsometric Map of Goals and Objectives .................. 5 VERTCON Predictions ................ 12 Existing SEWRPC Leveling Networks .... 5 Conclusions and Recommendations ...... 14 LIST OF APPENDICES Appendix Page A VERTCON Documents 19 A-I VERTCON Version 2.0 21 A-2 VERTCON Version 2.0 - Input Options ........................................ 24 A-3 VERTCON Version 2.0 - Output Formats .....................................
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