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GIS Expo 2014: Transformations between the geodetic datums of hawaii
1. US Army Corps of Engineers
BUILDING STRONG®
Sarah Falzarano, GISP
14 March 2014
Transformations between the
Geodetic Datums of Hawaii
Using ArcGIS
2. BUILDING STRONG®
Coordinate Systems
Geographic Coordinate
System
Projected Coordinate
System
X and Y values will vary depending on horizontal datum
3. BUILDING STRONG®
Geodetic Datum
The earth is not a perfect sphere
►Bulge at the equator
Using a combination of an ellipsoid and
geoid, a datum is born
►Creates the best possible fit
• Specific to a geographic location
Used in conjunction with a coordinate
system
4. BUILDING STRONG®
Coordinate Systems and
Datums for Hawaii
Coordinate System
Geographic
Hawaii State Plane
UTM
Datum
WGS 1984
NAD 1983
► NAD 1983 (1986)
► NAD 1983 HARN (1993)
► NAD 1983 PA11 (2011)
Old Hawaiian Datum
5. BUILDING STRONG®
NGS Adjusted NAD83
National Adjustment of 2011
NAD83 PA11 for the Pacific Plate
► State of Hawaii
► American Samoa
► Republic of the Marshall Islands
NAD83 MA11 for the Mariana Plate
► Commonwealth of the Northern Mariana Islands
► Guam
► Palau
NAD83 2011 for North America
6. BUILDING STRONG®
CORS Stations
Use NAD83 PA11
►Sometimes this is referred to as NAD83
2010.00 epoch
►Many surveyors refer to NAD83 epoch 2010
• Or they may report their data simply as NAD83
• If it is recent data, it is most NAD83 PA11
9. BUILDING STRONG®
Datum Transformations
Designed for a particular area
Have associated errors
Errors compound every time a
transformation is done
Consistency is key
►Use the same transformation each time
18. BUILDING STRONG®
ArcGIS Projection and Transformation
Files Specific to Hawaii
Version 10.2.1
►Includes files
Prior to version 10.2.1
►Will need to copy files to your profile
►Composite transformations not available prior
to 10.1
►Contact myself or Craig Clouet for files and
instructions
Mix and match coordinate systems and datums.Datums can have different realizations. Think of it as a different flavor of NAD83.
Don’t let the terminology fool you. NAD83 PA11 and NAD83 epoch 2010.00 are the same. In addition, some surveyors just report their data in NAD83 and disregard the realization they are using. However, if they tie into a CORS station, they are using NAD83 PA11.
Here’s the NGS datasheet for the ZHN1 CORS station showing that it is using NAD83 PA11 epoch 2010.00
Have you all seen this map provided by ESRI? It outlines the State Plane zones and UTM zones, but you’ll also notice an inset that describes the difference between NAD83 datum realizations for a particular NGS benchmark. The difference between datum realizations will vary depending on your geographic location, so it is not a straight shift of coordinates from one datum realization to another.
In this example, I’m projecting data from NAD83 PA11 to NAD83 HARN (normally, you would go the opposite way, but this is just an example). You’ll notice that a geographic transformation is prepopulated by ArcGIS. However, this may not be the best transformation to use. If you click on the down arrow, you’ll find other options available. How do you know which one is the best?
In this example, I’m projecting data from NAD83 PA11 to NAD83 HARN (normally, you would go the opposite way, but this is just an example). You’ll notice that a geographic transformation is prepopulated by ArcGIS. However, this may not be the best transformation to use. If you click on the down arrow, you’ll find other options available. How do you know which one is the best?
If you’ve been practicing GIS in Hawaii for a few years, you may be familiar with the previous datum transformation recommendations from ESRI. This were recommendations based on the best available models and information at the time before NAD83 PA11 was available. However, since this document came out, things have changed a bit and some of these transformations are no longer recommended.
Here is a list of new recommendations with the associated error introduced with the transformation. That’s right – everytime you perform a transformation, you introduce a small amount of error into your data. I tried to capture every possible combination of transformation, from Old Hawaiian Datum to each of the flavors of NAD83 plus WGS84; from vanilla NAD83 to the other flavors plus WGS84, etc. You’ll see that some transformations are actually a combination of two transformations, called a composite transformation. If you would like a copy of these recommendations, you can contact me or Craig Clouet.