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Getting WGS84 GPS Data into ArcGIS
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http://www.wwu.edu/huxley/spatial/tut/GPS_to_ArcGIS.htm
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Getting WGS84 GPS Data into ArcGIS
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See also Adding X-Y Data to ArcGIS See also How to get data from Excel to ArcGIS
By default, GPS receivers record data in latitude-longitude using the WGS84 (World Geodetic System 1984) datum (WGS84 is “an earth fixed global reference frame, including an earth model.” See http://www.wgs84.com/wgs84/wgs84.htm). Many GPS receivers allow the user to view their location in local coordinates as well (e.g., UTM, State Plane, etc.), performing a translation from WGS84 to the desired coordinate system (and datum). Similarly, some GPS software packages allow you to convert to the coordinate system of your choice when you export your data. Often, however, GPS data can only be exported in WGS84, typically as a text file with X-Y coordinates along with an ID, a time stamp, altitude and/or other information. Steps for bringing this “raw” GPS data successfully into ArcGIS are outlined below.
Note that this information is somewhat written for our local datasets (i.e., converting WGS84 GPS data to the commonly used coordinate systems in the WWU area: UTM zone 10 North, and State Plane WA North, NAD83 or NAD27). If you have data that is already in a projected coordinate system (something other than WGS84, e.g. UTM or State Plane) than you can still follow the basicAdd XY Data instructions.
Getting Data From the GPS The process of getting your data out of a GPS receiver will vary depending upon the type of receiver and/or the GPS software being used. For the purposes of this tutorial, it is assumed that the GPS data is in a standard ASCII text file, with commas or tabs delimiting the columns of information (not spaces). These columns should include (at the very least) an X (Longitude) and Y (Latitude) field in decimal degrees (if your data is in degrees, minutes and seconds you will need to convert it to decimal degrees). For best results, make sure that the text file: Is TAB or COMMA delimited (not space) Has only one header row containing the names of the fields Uses only standard alpha-numeric characters in the field names Has no more than 8 characters and no spaces in the field names Has no blank rows Has no extra rows of information below the data X and Y fields must be numeric
Using WGS84 GPS Data in a WGS84 Datum Open ArcMap
Optional: Add Data (from the File menu choose Add Data)
Check/Set the Coordinate System and Datum From the View menu choose Data Frame Properties In the Data Frame Properties window: Click the Coordinate System tab Make sure the Current coordinate system is WGS84 (e.g. GCS_WGS_1984). If not: Use the browse window below Select a coordinate system: to browse to the desired system using a WGS84 datum, e.g., Predefined | Geographic Coordinate Systems | World | WGS 1984
Add GPS data to ArcMap From the Tools menu choose Add XY Data… In the Add XY Data window: Choose a table… Browse to your data file X Field = <Longitude> (or whatever your E-W field is named) Y Field = <Latitude> (or whatever your N-S field is named) For the Spatial Reference of Input Coordinates | Description: (by default this will say “Unknown Coordinate System”) Click on Edit (below the Description box) In the Spatial Reference Properties window, press Select In the Browse for Coordinate System window browse to: Geographic Coordinate Systems | World | WGS 1984 Press Add Back in the Spatial Reference Properties window, press OK Back in the Add XY Data window, Press OK
Optional: Export data to a WGS84 shapefile: Right-click on X-Y data in the Table of Contents and choose Data | Export Data… In Export Data window: Check Use the same Coordinate System as the data frame Rename and/or change the storage location of the new shapefile as desired in the Output shapefile box Click OK
Using WGS84 GPS Data w/a NAD83 or NAD27 Datum Frequently, GPS data will need to be used in conjunction with local data sets using a NAD83 or NAD27 datum. (NOTE: While the instructions below use ArcMap, ArcToolbox can also be used for defining the projection of your data and/or for re-projection from one datum to another, however, make sure to use the proper Geographic Transformations as discussed above). In brief, there are two methods of getting WGS84 GPS data into NAD83 or NAD27 coordinate systems The first of these is to assign a NAD83 datum for the GPS data (even though the data is actually WGS84) (See discussion on why a NAD83 datum works for WGS84 data below) and provides a simpler, more rapid process for viewing and using the GPS data. The second option requires a few additional steps but should produce slightly better results. Experimental tests indicate that the difference between the two methods to be less than 2 meters. Given the inherent inaccuracy of GPS, the first method may well be “good enough” for most applications. These methods are outlined below, with more complete details on the following pages: Method 1 – WGS84 to either NAD83 or NAD27 (define the data as NAD83, even though its really WGS84)
Method 2a WGS84 to NAD83 (define the data as WGS84, re-project to NAD83)
Method 2(b) WGS84 to NAD27 (first get the data to NAD83, then re-project it to NAD27)
Method 1a Details: Using WGS84 data in a NAD83 Datum
Open ArcMap Optional: Add Data (File | Add Data) Check/Set the Coordinate System and Datum: View | Data Frame Properties In the Data Frame Properties window: Click the Coordinate System tab If the Current coordinate system isn’t NAD83: In the box below Select a coordinate system: browse to the desired system using a NAD83 datum (e.g., Predefined | Projected Coordinate Systems | UTM | Nad 1983 | NAD 1983 UTM Zone 10N or Predefined | Projected Coordinate Systems | State Plane | Nad 1983 | NAD 1983 StatePlane Washington North FIPS 4601) Add GPS data to ArcMap From the Tools menu choose Add XY Data… In the Add XY Data window: Choose a table… Browse to your data file X Field = <Longitude> (or whatever your E-W field is named) Y Field = <Latitude> (or whatever your N-S field is named) For the Spatial Reference of Input Coordinates | Description: (by default this will say “Unknown Coordinate System”) Click on Edit (below the Description box) In the Spatial Reference Properties window, press Select In the Browse for Coordinate System window browse to: Geographic Coordinate Systems | North America | North American Datum 1983.prj Press Add Back in the Spatial Reference Properties window, press OK Back in the Add XY Data window, Press OK
Optional: Export data to a NAD83 shapefile (right-click on X-Y data in the Table of Contents and choose Data | Export Data… In Export Data window: Check Use the same Coordinate System as the data frame Rename and/or change the storage location of the new shapefile as desired in the Output shapefile box Click OK
Method 1b Details: Using WGS84 data in a NAD27 Datum
Open ArcMap - Optional: Add Data (File | Add Data) Check/Set the Coordinate System and Datum View | Data Frame Properties In the Data Frame Properties window: Click the Coordinate System tab If the Current coordinate system isn’t NAD27: In the box below Select a coordinate system: browse to the desired system using a NAD27 datum (e.g., Predefined | Projected Coordinate Systems | UTM | Nad 1983 | NAD 1983 UTM Zone 10N or Predefined | Projected Coordinate Systems | State Plane | Nad 1983 | NAD 1983 StatePlane Washington North FIPS 4601) Add GPS data to ArcMap From the Tools menu choose Add XY Data… In the Add XY Data window: Choose a table… Browse to your data file X Field = <Longitude> (or whatever your E-W field is named) Y Field = <Latitude> (or whatever your N-S field is named) For the Spatial Reference of Input Coordinates | Description: (by default this will say “Unknown Coordinate System”) Click on Edit (below the Description box) In the Spatial Reference Properties window, press Select In the Browse for Coordinate System window browse to: Geographic Coordinate Systems | North America | North American Datum 1983.prj Press Add Back in the Spatial Reference Properties window, press OK Back in the Add XY Data window, Press OK
Optional: Export data to a NAD27 shapefile (right-click data layer in the Table of Contents and choose Data | Export Data… In Export Data window: Check Use the same Coordinate System as the data frame Rename and/or change the storage location as desired Click OK
Method 2a Details: Using WGS84 data in a NAD83 Datum Open ArcMap Optional: Add Data (File | Add Data) Check/Set the Coordinate System and Datum: View | Data Frame Properties In the Data Frame Properties window: Click the Coordinate System tab If the Current coordinate system isn’t NAD83: In the box below Select a coordinate system: browse to the desired system using a NAD83 datum (e.g., Predefined | Projected Coordinate Systems | UTM | Nad 1983 | NAD 1983 UTM Zone 10N or Predefined | Projected Coordinate Systems | State Plane | Nad 1983 | NAD 1983 StatePlane Washington North FIPS 4601) Add GPS data to ArcMap From the Tools menu choose Add XY Data… In the Add XY Data window: Choose a table… Browse to your data file X Field = <Longitude> (or whatever your E-W field is named) Y Field = <Latitude> (or whatever your N-S field is named) For the Spatial Reference of Input Coordinates | Description: (by default this will say “Unknown Coordinate System”) Click on Edit (below the Description box) In the Spatial Reference Properties window, press Select In the Browse for Coordinate System window browse to: Geographic Coordinate Systems | World | WGS 1984 Press Add Back in the Spatial Reference Properties window, press OK Back in the Add XY Data window, Press OK
Open the View | Data Frame Properties In the Data Frame Properties window: Click the Coordinate System tab Click on the Transformations… button In the Geographic Coordinate System Transformations box: Select GCS_WGS_1984 in the Convert from: box Select NAD_1983_To_WGS_1984_5 in the using: box Click OK to close the Transformations window Click OK to close the Data Frame Properties window
Optional: Export data to a NAD83 shapefile (right-click on X-Y data in the Table of Contents and choose Data | Export Data… In Export Data window: Check Use the same Coordinate System as the data frame Rename and/or change the storage location of the new shapefile as desired in the Output shapefile box Click OK
Method 2b Details: Using WGS84 data in a NAD27 Datum
Complete the Steps detailed in 2a above (bringing WGS84 GPS data into ArcMap and converting it to NAD83 data, exported to a shapefile).
Open the View | Data Frame Properties In the Data Frame Properties window Click the Coordinate System tab Use the browse window below Select a coordinate system: to browse to the desired system using a NAD27 datum Click on the Transformations… button In the Geographic Coordinate System Transformations box: Select GCS_North_American_1983 in the Convert from: box Select NAD_1927_To_NAD_1983_NADCON under using: Click OK to close the Transformations window Click OK to close the Data Frame Properties window
Optional: Export data to a NAD27 shapefile (right-click data layer in the Table of Contents and choose Data | Export Data… In Export Data window: Check Use the same Coordinate System as the data frame Rename and/or change the storage location as desired Click OK
For our part of the world, WGS84 and NAD83 are very close to being the same. This is why Method 1 above (simply defining your WGS84 data as NAD83) works.
However, for ArcMap to use WGS84 data in a NAD27 data frame, a Geographic Transformation must be applied to the data. In the case of WGS84 to NAD27, this involves a mathematical calculation that inevitably introduces a certain amount of error. On the other hand, for Geographic Transformations between NAD83 and NAD27 a much more precise “grid-based” transformation can be used (NADCON: see also http://www.ngs.noaa.gov/TOOLS/Nadcon/Nadcon.html). Because the shift between the two datums is not uniform across the entire country there is no single equation that can be applied. Instead, the grid-based transformation uses a series of locally appropriate coordinate calculations (based on a data file which contains the actual datum shift at each point in a network of grid points) to more precisely convert data. Since WGS84 and NAD83 are almost identical, calling your GPS data NAD83 allows ArcMap to use the more accurate grid-based method of transformation, and will typically give better results than transforming directly from WGS84 to NAD27.
A more precise method is to define the data as WGS84, then use ArcGIS to convert from WGS84 to NAD83 (using NAD_1983_To_WGS_1984_5 for theGeographic Transformation recommended), and then using the NADCON Geographic Transformation to convert from NAD83 to NAD27. This two-step process takes into account the slight differences between WGS84 and NAD83, while also taking advantage the superior NADCON geographic transformation to convert to NAD27.
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