welcome handouts available joel cusick national park service alaska regional office...
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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
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