Preparing Minnesota’s Coordinate Systems for 2022 · Transverse Mercator Oblique Mercator...

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Preparing Minnesota’s Coordinate Systems for 2022

Geoff Bitner, LSMnDOT/NGS State Geodetic Coordinator

67th MSPS Annual MeetingFebruary 15, 2019

Collect in Coordinates

Compute in Coordinates

Construct in Coordinates

Grid Coordinates are Everywhere

Coordinate Systems Will Need Updating

New datum in 2022 (Reference Frame)

• Expect coordinate shifts of ≈ 1.0m‐1.5m

• Expect elevation shifts of ≈ ‐0.75m

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Purpose of Today’s Presentation

• Cover some coordinate system basics

• Look at available methods and options

• Review a brief history of coordinate systems in MN

• Look at the future of the County Coordinate system

• Discuss State Plane for 2022

Grid Coordinate System

• A rectangular (Cartesian) system based on straight line distances which approximate measurements upon the surface of the Earth

• An ordered pair of perpendicular axis

Source: By K. Bolino - Made by K. Bolino (Kbolino), based upon earlier versions., Public Domain, https://commons.wikimedia.org/w/index.php?curid=869195

Issues with Grid Systems

• Projections or flattening the sphere

• Consider the size and shape of the project area

• Distortions or dealing with scale

• Consider the effects of distance and elevation

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Three Common Projections

◦ Lambert Conic

◦ Transverse Mercator

◦ Oblique Mercator


◦ Lambert Conic



Source: The Minnesota County Coordinate System: a handbook for users; Whitehorn, Kenneth; St. Cloud, MN, 1997, Fig. 4

Source: Oregon Coordinate Reference System, Handbook and User Guide, available at ftp://ftp.odot.state.or.us/ORGN/Documents/ocrs_handbook_user_guide.pdf


◦ Lambert Conic



Properties of a Lambert Conic

• Think of a cone placed over a sphere

• Good for areas long in the east/west direction

• May intersect the ellipsoid along two parallels (secant) or one (tangent)

• Used in State Plane and many MN County coordinates

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◦ Lambert Conic



Source: The Minnesota County Coordinate System: a handbook for users; Whitehorn, Kenneth; St. Cloud, MN, 1997, Fig 5.



◦ Lambert Conic



Properties of Transverse Mercator

• Think of a cylinder placed over a sphere, parallel with the equator

• Good for areas long in the north/south direction

• Best known for its use in the Universal Transverse Mercator (UTM) grid system

• Also used in several MN County coordinates


◦ Lambert Conic





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◦ Lambert Conic



Properties of Oblique Mercator

• Think of a cylinder placed over a sphere and rotated for best fit

• Best known in Minnesota for its use along the North Shore of Lake Superior

• Can be difficult to model in software and field controllers



Issues with Grid Systems

• Projections or flattening the sphere

• Consider the size and shape of the project area

• Distortions or dealing with scale

• Consider the effects of distance and elevation

Two Types of Distortion

Linear

• Often thought of as a ratio of distortion related to distance

+/‐ 20 ppm (mm/km)+/‐ 0.11 ft/mile1:50,000

• Can be positive or negative

Angular

• Known as the convergence angle for conformal projections

• Or, the difference between grid north and geodetic north

• The convergence angle increases with distance from the central meridian

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Linear Distortion

• Negative DistortionGrid shorter than Ground

• Positive DistortionGrid longer than Ground

Source: Understanding the State Plane Coordinate System, available at http://www.ngs.noaa.gov/PUBS_LIB/UnderstandingSPC.pdf

Linear Distortion due to Earth Curvature


Linear Distortion due to Ground Ht vs. Plane Ht


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Distortion Example Between Grid Systems

Earth SurfaceEllipsoid

Ellipsoid Semi‐major Semi‐minor

GRS80 6,378,137.0 6,356,752.3141

Crow Wing 6,378,546.96 6,357,160.896


Ellipsoid Semi‐major Semi‐minor

GRS80 6,378,137.0 6,356,752.3141

Crow Wing 6,378,546.96 6,357,160.896

Expands ellipsoid height by ≈ 410m

JONES 2Ellip Ht. 370.5m

RABBIT RESETEllip. Ht. 397.5m


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Expands ellipsoid height by 409.957m

JONES 2RABBIT RESET

UTM15

57,726.63’ State Plane

14.64ft 57,741.27’ Crow Wing Cnty

22.27ft 7.63ft 57,748.90’








Grid System Options

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Grid System Options

Use an Existing Coordinate System

1. State Plane or UTM

Create a Coordinate System to Minimize Distortion

1. Modify an existing system – State Plane/UTM

2. Modify the ellipsoid – Effectively altering the datum

3. Develop a modern Low Distortion Projection system such as those in Iowa, Kansas, Indiana, or Wisconsin

Popular Coordinate Systems in MN

Universal Transverse Mercator or UTM

In MN – UTM15 E “E” is for Extended

• Developed in the 1940s• Zone widths, 6° Longitude• Scale less than 1:2,500

≈½ per mile• Great for GIS and large scale planning

Source: http://www.history.noaa.gov/stories_tales/geod1.html


State Plane Coordinate System – (not so popular?)

• C&GS for civilian use• Developed in 1930s• Defined by state/county• Three zones in MN based on Lambert Conic prj.

• Distortion ≈ 1:10,500

Source: https://geodesy.noaa.gov/SPCS/index.shtml

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UTM andState Plane


Justification for Minimizing Distortion

• Eliminates the need to scale coordinates and reduces the chance for conversion error

• Measurements are close to being 1‐to‐1, i.e.,

1 foot in the field = 1 foot in the office

• Angles in the field match angles in the office

• Modern systems can be developed for easy use in software, standardized procedures, and universal acceptance

Some Options

A. Use an Existing Coordinate System

• State Plane or UTM

B. Create a Coordinate System to Minimize Distortion

1. Modify an existing system – State Plane/UTM

2. Modify the ellipsoid – Effectively altering the datum

3. Develop a modern Low Distortion Projection system such as those in Iowa, Kansas, Indiana, or Wisconsin

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Controlling Distortion

1. Modify Existing System

State PlaneEarth Surface

Ellipsoid


2. Modify the Ellipsoid





2. Modify the Ellipsoid

3. Create a Low Distortion Projection (LDP)


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Some Options

Coordinate System OptionsIt’s about understanding and managing distortions

• Do Nothing… not so good

• State Plane or UTM… good for large areas (statewide)

• Low Distortion Projections… good for small areas (local)







Brief History in MN

1930s & ‘40s – State Plane

1960s – Modify State Plane

1970s – Modified State Plane/Roscoe project system

1980s – Minnesota County Coordinate System

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Minnesota Dept of Highways Datum

A modified system based on State Plane

State PlaneEarth Surface

Ellipsoid

Minnesota Dept of Highways Datum

• Developed in early 1968• Zones generally follow SPCS

Distortion Goals:1:10,000 (rural)1:20,000 (urban)

Minnesota Project Coordinate System

• Developed in early ‘70s• Zones defined by:

• 1° Long. / 15’ Lat.• Conforms to USGS

Distortion Goals:1:30,000

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A modified ellipsoid system to achieve low distortions

Minnesota County Coordinate System



• Developed in 1985• Zones generally defined by county boundaries

Distortion Goals:1:50,000 (rural)1:100,000 (urban)


• 87 Counties

• 67 unique ground planes

• Low distortions ≈0.10ft/mileor better

• Secant planes

• Modified ellipsoids

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County Plane Coordinate System Project

Conducted by Steven Rick Brown June 1984 – March 1985• Followed methods promoted by NGS

• Preliminary work done by hand• Specific programs were developed to speed analysis

• Reliance on USGS quad maps for elevations and positions (lat/long)








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• Smaller zones

• Multiple names for single set of parameters

• Difficult to model parameters in modern software

• Inconsistent with modern practice – i.e., modified ellipsoid & secant to ellipsoid

Current County Coordinate System

Challenges with the existing County Coordinate System


Benefits of Modernizing

Low Distortion Projection

• Larger zones with similar performance to Cnty Coord.

• Eliminates the issues with a modified datum

• Works seamlessly with modern software

• Regional approach reduces the number of transition zones

• May be accepted by NGS

Modern Low Distortion Projection (LDP) system

Current County Coordinate System

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Iowa Regional Coordinate System

Kansas Regional Coordinate System

Minnesota Regional Coordinate System

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Criteria for Consideration

• Determine acceptable distortion: ≈ 20ppm or 0.10ft/mile

• Consider project area & terrain relief: ≈ 70 miles wide and 800ft vertical differential

• Determine best projection:Lambert Conformal Conic & Transverse Mercator

• Break on county boundaries

Criteria for Consideration

• Other Considerations:

• Transportation corridors• Geographical limiters: rivers, lakes, bluffs, etc.• Urban areas: Mankato, Moorhead, St Cloud, Minneapolis/St Paul

• Resource sharing: Dodge/Goodhue, Lac Qui Parle/Chippewa

• County partnerships: Stearns/Sherburne/Wright• GIS regional groups… to a lesser degree

Our Old Friend… Distortion


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Example Distortion Maps

Example Distortion Maps – Changing Plane Ht.

Central Meridian: 94°22’, Ht:225m Central Meridian: 94°22’, Ht:275m

Central Meridian: 94°15’, Ht:275m Central Meridian: 94°30’, Ht:275m

Example Distortion Maps – Changing Meridian

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Central Meridian: 94°24’, Ht:250m Three Regions Instead of One

Example Distortion Maps – Changing Meridian

Two Zone Metro

Single Zone

Example Distortion Maps – Metro Options

Project Timeline

1. 2015 – Began with an initial report

2. 2016 – Stagnated, some discussion

3. 2017 – Staffing changes, recognized need, debate in‐house vs. outsourcing

4. 2018 – Created TAP group, developed preliminary design criteria, creating preliminary maps and data for review

5. 2019 – Will refine design criteria, finalize regions, complete parameters by December 2019, feedback and outreach

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MnDOT’s Proposal

February 2018 – MnDOT began efforts to propose a single State Plane zone.

• Met with MSPS Board, MnGEO, and DNR

• Letter included in Minnesota Surveyor, summer 2018, Vol. 28, No. 1

State Plane Background Information

A Little History

• Developed in 1930s

• Considered a practical solution for engineering

• Three zones in MN

• Distortions ≈ 1:10,000 on the ellipse or ≈ ½ ft/mile

• Never really “took off”

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UTM 15 for Statewide & Regional Mapping

• UTM misused for statewide mapping

MN Spatial Data Exchange Standard

UTM Background Information

• UTM misused for statewide mapping

• Becomes problematic when using GPS and online positioning services

• Distortions ≈ 1:2,500 that’s ≈ 2 ft./mile

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Single State Plane Zones

Other states with a single zone:

• Montana• Nebraska• Tennessee• South Carolina

Justification for a Single Zone

• Current SPCS not used

• UTM is misused

• Simplify legislation

• NGS will do the work

• Provide a legitimate coordinate system for regional and statewide planning purposes

Timeline and Next Steps

1. Development of new reference frame (datum) in 2022 is driving this proposal and timeline

2. NGS has indicated that a single zone for Minnesota will be developed without requiring an “official” request

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Links to Federal Register &NGS Policy, Procedure, and SPCS website

• NGS State Plane Coordinate System website ‐https://www.ngs.noaa.gov/SPCS/index.shtml

• History of State Plane ‐ NGS Policy ‐https://www.ngs.noaa.gov/library/pdfs/NOAA_SP_NOS_NGS_0013_v01_2018‐03‐06.pdf

• NGS Draft Policy ‐https://www.ngs.noaa.gov/INFO/Policy/files/DRAFT_SPCS2022_Policy.pdf

• NGS Draft Procedure ‐https://geodesy.noaa.gov/INFO/Policy/files/DRAFT_SPCS2022_Procedures.pdf

Summary

• Covered some coordinate system basics

• Looked at available methods and options

• Reviewed a brief history of coordinate systems in MN

• Looked at the future of the County Coordinate system

• Discussed State Plane for 2022

Questions?

Geoff Bitner, LS

[email protected]

651‐366‐3490

Date post:	30-May-2020
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