WELCOME Handouts Available Joel Cusick National Park Service Alaska Regional Office Joel Cusick National Park Service Alaska Regional Office Paper Presented to: ESRI Survey and GIS Summit, August 2006 Sunday, August 6, 2006 San Diego, CA Paper Presented to: ESRI Survey and GIS Summit, August 2006 Sunday, August 6, 2006 San Diego, CA

Are You Really Mapping Submeter? Revenge of the Shift

Fire Hydrant Survey Survey GPS Transform: NAD27 to WGS84_4

The Wrong Place 50 feet

Revenge of the Shift

NAD27-NAD83 N 61º 33’ 50.0” W 149º 44’ 21.0” NAD27 N 61º 33’ 50.0” W 149º 44’ 21.0” NAD83 200’ – 800’ horizontal

The Insidious Shifts 3’ – 50’ horizontal NAD83 – WGS84/ITRF00

Objective  Verify Datum Used in GIS  Confirm Reference Frame of GPS  Apply the Correct Transformation  Verify Datum Used in GIS  Confirm Reference Frame of GPS  Apply the Correct Transformation

Step 1. Verify Datum in GIS  GIS as a blender  Datum Transformations  Standardize on NAD83  Scale  GIS as a blender  Datum Transformations  Standardize on NAD83  Scale

GIS as a Blender  It’s the GIS Way

Datums and Shifts  Most all coordinate systems are referenced to a specific datum  Mix two different datums for the same point  Most all coordinate systems are referenced to a specific datum  Mix two different datums for the same point

Datum Shift Errors  Datum shift errors are realized when different datums are mixed and wrong assumptions are made

Datum Transformations  Formula to convert between two datums  Legacy GIS  Thousands  Move GPS data data to/from GIS  WGS84_To_??  Formula to convert between two datums  Legacy GIS  Thousands  Move GPS data data to/from GIS  WGS84_To_??

Datum Transformations  In a GIS They Work Both Ways

Datum Transformations  You Can’t Go Back!  Human Error is the Cause  Lack of documentation  Fundamental principle behind Mobile GIS  You Can’t Go Back!  Human Error is the Cause  Lack of documentation  Fundamental principle behind Mobile GIS

Standardize on NAD83  If you are using GPS data you should be in NAD83 Alaska - Part of the Continental United States since 1867! …But Still using the 1866 Spheroid

What’s Wrong with NAD27  Best fitting to just North America  Non Geocentric  Significant scale and azimuth distortion  Poorly determined relationship to the geoid  Best fitting to just North America  Non Geocentric  Significant scale and azimuth distortion  Poorly determined relationship to the geoid

Standardize on NAD83  Dave Doyle in Alaska February 2005  Cousin Vinny  Dave Doyle in Alaska February 2005  Cousin Vinny * Dave Doyle, Senior Geodesist – NGS, Alaska Survey and Mapping Conference, Anchorage Alaska.

Standardize on NAD83  Convert NAD27 to NAD83 using NADCON  Cases where NADCON is not a good idea  USFS reliance on PLGR’s from mid 1996 to 2000  Convert NAD27 to NAD83 using NADCON  Cases where NADCON is not a good idea  USFS reliance on PLGR’s from mid 1996 to 2000

Unusual NAD27 Conversion Cases * Andrew Lister, Research Forester, USDA Forest Service,

– Mark Roper

Scale – Worry or Not?  GIS Data Scales  Data digitized at 1:24,000  NMAS states - +/- 40 feet  Mapping GPS Errors  Large - Autonomous GPS (pre SA)  Mid - PLGR / Autonomous GPS Today  Small - Mapping Grade  GIS Data Scales  Data digitized at 1:24,000  NMAS states - +/- 40 feet  Mapping GPS Errors  Large - Autonomous GPS (pre SA)  Mid - PLGR / Autonomous GPS Today  Small - Mapping Grade

Step 1. Verify Datum in GIS  Standardize on NAD83!  Convert NAD27 to NAD83 using NADCON  Special Cases Require Care  Consider Scale of Data  Standardize on NAD83!  Convert NAD27 to NAD83 using NADCON  Special Cases Require Care  Consider Scale of Data

I’m in NAD83 WGS84 /ITRF00 Step 2. Confirm the GPS Reference Frame  Which Reference Frame are you In?

Datum Adjustments  WGS84 (G1150) – most current version  “Original” NAD83 = NAD83 (1986)  NAD83 (1992)  NAD83 (2002)………….  NAD83 (CORS96) (Epoch )  WGS84 (G1150) – most current version  “Original” NAD83 = NAD83 (1986)  NAD83 (1992)  NAD83 (2002)………….  NAD83 (CORS96) (Epoch )

Over Time Datums Have Grown Apart NAD83 (1986) = WGS84 WGS84 = ITRF00 (2cm) NAD83 ~ 1 meter

Which Reference Frame are You In?  CORS users are in ITRF00

Which Reference Frame are You In?  Since you corrected against a CORS station…

Which Reference Frame Are You In? NAD83 (CORS96)  NDGPS (Beacon)  OMNISTAR (Satellite)  CORS Post Processed  Autonomous GPS  WAAS WGS84 (G1150) ITRF00 =

GPS Base Station Providers  The Trick is knowing what reference frame

Step 2. Confirm the GPS Reference Frame  Which Reference Frame Are You In?

Step 3. Apply the Correct Transformation  Use Zero Transformations when Appropriate  If NDGPS differential  NAD83 Reference Frame  If post-process CORS, WAAS – ITRF00 Reference Frame  Transform using NAD83 (CORS96)  Use Zero Transformations when Appropriate  If NDGPS differential  NAD83 Reference Frame  If post-process CORS, WAAS – ITRF00 Reference Frame  Transform using NAD83 (CORS96) See Handout for Trimble and ArcPad Users

Avoid the Shift  GIS Community  Surveyors  Software Developers  GIS Community  Surveyors  Software Developers

Avoid the Shift  GIS Community

Avoid the Shift  GIS Community  Test Against Control  GIS Community  Test Against Control 

Avoid the Shift  Surveyors  Communicate better in map products, digital data and reference stations  Surveyors  Communicate better in map products, digital data and reference stations

Avoid the Shift  Software Developers  Standardize Syntax  Enhance Datum Interfaces  Software Developers  Standardize Syntax  Enhance Datum Interfaces

Avoid the Shift  Software Companies  Standardize Syntax  Enhance Datum Interfaces  Embed Transformation Used inside Data Layers  Software Companies  Standardize Syntax  Enhance Datum Interfaces  Embed Transformation Used inside Data Layers MXGPS

Conclusion  Verify Datum in GIS  Confirm Reference Frame  Apply the Correct Transform  Verify Datum in GIS  Confirm Reference Frame  Apply the Correct Transform

Acknowledgements  Carl Beyerhelm, USFS  Ron Bisio – Trimble  Shane Clarke - ESRI  Michael Dennis, Geodetic Analysis  David Doyle, NGS  Melita Kennedy, ESRI  Andrew Lister, USFS  Mark Roper, USFS  Mel Philbrook, Trimble  Myles Sutherland, ESRI  Carl Beyerhelm, USFS  Ron Bisio – Trimble  Shane Clarke - ESRI  Michael Dennis, Geodetic Analysis  David Doyle, NGS  Melita Kennedy, ESRI  Andrew Lister, USFS  Mark Roper, USFS  Mel Philbrook, Trimble  Myles Sutherland, ESRI