WELCOMEWELCOME

Handouts AvailableHandouts Available

Joel CusickNational Park ServiceAlaska Regional OfficeJoel_cusick@nps.gov

Joel CusickNational Park ServiceAlaska Regional OfficeJoel_cusick@nps.gov

Paper Presented to:ESRI Survey and GIS Summit, August 2006

Sunday, August 6, 2006San Diego, CA

Paper Presented to:ESRI Survey and GIS Summit, August 2006

Sunday, August 6, 2006San Diego, CA

Are You Really

Mapping Submeter? Are You Really

Mapping Submeter? Revenge

of the Shift

Revenge of the Shift

Fire Hydrant SurveyFire Hydrant Survey

Survey GPS

Transform:

NAD27 to WGS84_4

The Wrong PlaceThe Wrong Place

50 feet

Revenge of the ShiftRevenge of the Shift

NAD27-NAD83NAD27-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 ShiftsThe Insidious Shifts

3’ – 50’horizontal

NAD83 – WGS84/ITRF00

NAD83 – WGS84/ITRF00

ObjectiveObjective

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 GISStep 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 BlenderGIS as a Blender

It’s the GIS Way It’s the GIS Way

Datums and ShiftsDatums 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 ErrorsDatum Shift Errors

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

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

Datum TransformationsDatum 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 TransformationsDatum Transformations In a GIS They Work Both

Ways In a GIS They Work Both

Ways

Datum TransformationsDatum 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 NAD83Standardize on NAD83 If you are using GPS data

you should be in 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 NAD27What’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 NAD83Standardize on NAD83

Dave Doyle in Alaska February 2005

Cousin Vinny

Dave Doyle in Alaska February 2005

Cousin Vinny

* Dave Doyle, Senior Geodesist – NGS, 2005. Alaska Survey and Mapping Conference, Anchorage Alaska.

Standardize on NAD83Standardize 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 CasesUnusual NAD27 Conversion Cases

* Andrew Lister, Research Forester, USDA Forest Service, 2005. email

– www.fs.fed.us/database/gps Mark Roper

Scale – Worry or Not?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 GISStep 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 FrameStep 2. Confirm the GPS Reference Frame

Which Reference Frame are you In?

Which Reference Frame are you In?

Datum AdjustmentsDatum Adjustments

WGS84 (G1150) – most current version

“Original” NAD83 = NAD83 (1986) NAD83 (1992) NAD83 (2002)…………. NAD83 (CORS96) (Epoch 1997.00)

WGS84 (G1150) – most current version

“Original” NAD83 = NAD83 (1986) NAD83 (1992) NAD83 (2002)…………. NAD83 (CORS96) (Epoch 1997.00)

Over Time Datums Have Grown ApartOver Time Datums Have Grown Apart

NAD83 (1986) = WGS84

WGS84 = ITRF00 (2cm) NAD83

~ 1 meter

Which Reference Frame are You In?Which Reference Frame are You In?

CORS users are in ITRF00 CORS users are in ITRF00

Which Reference Frame are You In?Which Reference Frame are You In?

Since you corrected against a CORS station…

Since you corrected against a CORS station…

Which Reference Frame Are You In?Which Reference Frame Are You In?

NAD83 (CORS96)

NDGPS (Beacon)OMNISTAR (Satellite)

CORS Post Processed Autonomous GPSWAAS

WGS84 (G1150)

ITRF00=

GPS Base Station ProvidersGPS Base Station Providers The Trick is knowing what

reference frame The Trick is knowing what

reference frame

Step 2. Confirm the GPS Reference FrameStep 2. Confirm the GPS Reference Frame

Which Reference Frame Are You In?

Which Reference Frame Are You In?

Step 3. Apply the Correct TransformationStep 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 ShiftAvoid the Shift GIS Community

Surveyors

Software Developers

GIS Community

Surveyors

Software Developers

Avoid the ShiftAvoid the Shift GIS Community GIS Community

Avoid the ShiftAvoid the Shift GIS Community

Test Against Control

GIS Community Test Against Control

http://www.ngs.noaa.gov/cgi-bin/ds_radius_sf.prl http://www.ngs.noaa.gov/cgi-bin/ds_radius_sf.prl

Avoid the ShiftAvoid 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 ShiftAvoid the Shift Software Developers

Standardize Syntax Enhance Datum Interfaces

Software Developers Standardize Syntax Enhance Datum Interfaces

Avoid the ShiftAvoid 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

•www.mxgeo.com/

ConclusionConclusion Verify Datum in GIS

Confirm Reference Frame

Apply the Correct Transform

Verify Datum in GIS

Confirm Reference Frame

Apply the Correct Transform

AcknowledgementsAcknowledgements 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