Coordinate Systems & Vertical Datum Issues Mark Seidelmann, PE, GISP Erick Lobao, GISP September 30, 2011 Photo Optional Excited to be here Partner could not be here Originally intended for more general audience Theme of the conference. You are here? Practical example of a common problem Not a surveyor

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. Definitions. Interchangeable jargon Significance of projections Live demo Feedback-non esri users Obvious take home- communicate and document Intro – Definitions – Significance –Tools & Tricks– Conclusions

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 Projections introduce Distortion. Some preserve some features better than others. Intro – Definitions – Significance – Tools & Tricks - Conclusions

Definitions Coordinate Systems: 6 5 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 How you describe your location? Two types of projections: Geographic uses Latitude and Longitude (angles measured from the center of the earth). Length is variable. Projected: Assumes a flat surface. Uses X,Y coordinates. Intro – Definitions – Significance – Tools & Tricks - Conclusions

Definitions Horizontal Datum: Where is origin (0,0)? Vertical Datum: 6 5 Horizontal Datum: Where is origin (0,0)? Vertical Datum: A reference surface from which elevation measurements are made. Where is Elevation 0 ft? ? In order to clearly share location information, Compare different data sets. You must know what origin your coordinate system references. Datums link spheroid (model of the earth, to specific parts of the earths surface). The earth is not a sphere, varies, datums help account for this. ? Intro – Definitions – Significance – Tools & Tricks - Conclusions

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 Different data producers have different needs, and therefore use different coordinate systems.

Example (Floodplain Mapping) Real world example of significance. Flood insurance Rate maps are a “regulatory” tool. Impact people. Location & Elevation help determine where flooding occurs. Datum shifts / impact coordinates and elevation values.

Datum Conversion It’s all Relative! House Elev. As maps get updated and Datums change, elevation values are impacted. Everything moves together. Can be difficult to communicate to home owners. 805 804 5 Flood Elev. 800 799 New Datum Old Datum

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 FEMA Reports specify & Document this. NOAA - NADCON software to generate & measure this. Use NADCON to Update legacy data

FIS and FIRM Data products impacted by datum changes. Flood insurance Study (report) Flood insurance Rate Map.

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

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

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)

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

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