Coordinate Systems & Vertical Datum Issues

1. Coordinate Systems & Vertical Datum Issues Mark Seidelmann, PE, GISP Erick Lobao, GISP September 30, 2011 Photo Optional

2. Introduction • Projections, datum's, and coordinate systems are an attempt to represent a 3 dimensional surface on a flat plane. • Real world significance (Floodplain Administrators). • Tips and Tricks. • Defining the Coordinate system and datum to be used early on avoids confusion later. Intro – Definitions – Significance –Tools & Tricks– Conclusions

3. Definitions • Map Projection: • A systematic representation of all or part of the surface of a round body on a plane. • Factors when picking a projection: • Area • Shape • Scale • Direction Intro – Definitions – Significance – Tools & Tricks -Conclusions

4. 6 5 Definitions • Coordinate Systems: • Reference System that uses numbers (coordinates) to define locations on a surface • Geographic: • Uses 3-d Surface • Latitude & Longitude • Length is variable • Projected: • Uses Flat Surface • X,Y • Length is constant Intro – Definitions – Significance – Tools & Tricks -Conclusions

5. 6 5 Definitions • Horizontal Datum: • Where is origin (0,0)? • Vertical Datum: • A reference surface from which elevation measurements are made. • Where is Elevation 0 ft? ? ? Intro – Definitions – Significance – Tools & Tricks -Conclusions

6. Common Coordinates in Ohio • Geographic: • World Geodetic System (WGS 84) • North American Datum 1983 (NAD83) • Projected: • State Plane – 2 zones North and South • NAD 27 • NAD 83 • NAD 83 HARN • UTM 16 and 17 north • Local Projections & Monuments • Projections for Different Purposes

7. Example (Floodplain Mapping)

8. 800 805 799 804 Datum Conversion It’s all Relative! House Elev. 5 Flood Elev. New Datum Old Datum

9. Datum Conversion • NADCON (NOAA) • NGVD 29 Vs. NAVD 88 • Vertical Datum Shift outlined in FEMA Guidelines and Specs Appendix B • Redelineated studies BFE’s haven’t changed • Datum shift is calculated for the county • Rarely shifted stream by stream

10. FIS and FIRM

11. Issue 1: Different Projections • Issues • All my data is in NAD83 State Plane Ohio South • New data is in UTM 17N. • Solution • Make sure the new data is defined as UTM 17N. • Project the dataset to NAD83 State Plane South. • Common Mistake • Redefining data to NAD83 State Plane South. Intro – Definitions – Significance – Tools & Tricks - Conclusions

12. Issue 2: Incorrect Projection • Issues • Projection on supplied data is incorrect or unknown. • Solution • Check Location. • Use data with known coordinates and compare. • Re-define Projection (start with the usual suspects). • Spatial adjustment tool • Common Mistake • Assuming the original projection was correct! Intro – Definitions – Significance – Tools & Tricks - Conclusions

13. Ohio Identify the Coordinate System • State Plane South NAD83 or NAD27 Feet • (1,300,000 to 2,500,000 , 145,000 to 1,470,000) • State Plane South NAD83 meters • (400,000 to 770,000 , 44,500 to 450,000) • State Plane North NAD83 or NAD27 Feet • (1,300,000 to 2,500,000 , -460,000 to 850,000) • State Plane North NAD83 meters • (400,000 to 770,000 , -141,000 to 260,000) • UTM NAD83 17 N • (168,000 to 540,000, 4,250,000 to 4,650,000) • Geographic • (38.462192 to 41.93089, -84.836426,-80.397949)

14. Conclusions • Knowing the coordinate system and datum of your data is essential. • Unknown / wrongly defined coordinate systems can cause delays and mistakes. • Understand impacts of Datum Changes to your data. Intro – Definitions – Significance – Tools & Tricks - Conclusions

15. Questions? • Erick Lobao, Stantec, Project Manager, GISP • erick.lobao@stantec.com • Mark Seidelmann, Stantec, Senior Project Engineer, PE, GISP • mark.seidelmann@stantec.com Intro – Definitions – Significance – Tools & Tricks - Conclusions