GIS Expo 2014: Transformations between the geodetic datums of hawaii
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Presentation by Sarah Falzarano, Army Corps of Engineers
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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
- 10. BUILDING STRONG® Projecting Data in ArcGIS
- 11. BUILDING STRONG® Projecting Data in ArcGIS
- 16. No longer recommended No longer recommended No longer recommended OutdatedDatumTransformation Recommendations
- 17. BUILDING STRONG® Recommended Datum Transformations From To Transformation Error (m) Old Hawaiian Datum NAD83 (86) Old_Hawaiian_To_NAD_1983 0.20 NAD83 HARN Old_Hawaiian_To_NAD_1983_HARN_Hawaii 0.05 NAD83 PA11 Old_Hawaiian_To_WGS_1984_8 + WGS_1984_(ITRF08)_To_NAD_1983_PA11 2.10 WGS84 Old_Hawaiian_To_NAD_1983_HARN_Hawaii + WGS_1984_(ITRF00)_To_NAD_1983_HARN 0.15 NAD83 (86) NAD83 HARN NAD_1983_To_HARN_Hawaii 0.05 NAD83 PA11 WGS_1984_(ITRF00)_to_NAD_1983 + WGS_1984_(ITRF08)_To_NAD_1983_PA11 0.15 WGS84 WGS_1984_(ITRF00)_To_NAD_1983 0.10 NAD83 HARN NAD83 PA11 WGS_1984_(ITRF08)_To_NAD_1983_PA11 + WGS_1984_(ITRF00)_To_NAD_1983_HARN 0.15 WGS84 WGS_1984_(ITRF00)_To_NAD_1983_HARN 0.10 NAD83 PA11 WGS84 WGS_1984_(ITRF08)_To_NAD_1983_PA11 0.05
- 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
Notas del editor
- 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.