Coordinate and Datum Transformations--Instructions

Windows users, be sure to read the section on performance issues.

Follow the links below to other sections of this document.

| General Information | User Interface Details | Performance Issues |

General Information

Using the Tool

Figure 1.  Coordinate and Datum
Transformations Tool User InterfaceThe Coordinate and Datum Transformations tool provides two coordinate display panes, an input pane and an output pane. You can enter coordinates in either geographics (decimal degrees) or UTM coordinates (meters) in the input pane on the left. The coordinate fields in the right-hand pane are for output only; they cannot be edited.

When you have finished entering a coordinate into one of the coordinate fields, use the Tab key or your mouse to move out of the coordinate field. The data in the other fields will be updated automatically.

You can select a different datum for each pane, and you can control the UTM zone to be used for the displayed UTM coordinates.

Datum Transformation Method

The Coordinate and Datum Transformations tool uses the standard Molodensky formulas for datum transformations. The tool uses the WGS 84 datum as its reference datum. Transformations between two non-WGS 84 datums are accomplished by first transforming from the input datum to WGS 84, then from WGS 84 to the output datum.

User Interface Details

Coordinate Display Panes

Figure 2.  Coordinate Display PaneAs described above, there are two data panes in the Coordinate and Datum Transformations tool's user interface. The left-hand pane is for data entry, and the right-hand pane is for displaying the result of a datum transformation.

Each pane displays the coordinates of a point in both geographic longitude and latitude (in decimal degrees) and in UTM x and y (in meters). The UTM display also indicates the zone (1-60) and the hemisphere (N or S).

Geographic Fields

Figure 3.  Geographic FieldsEnter data in these fields to specify a new location. Use decimal degrees, and use negative numbers to indicate West longitudes or South latitudes.

When you have finished entering data in one of the fields, use the Tab key or your mouse to move to another field. The data in the other fields will be updated automatically.

UTM Fields

Figure 4.  UTM FieldsEnter data in these fields to specify a new location. Use meters.

When you have finished entering data in one of the fields, use the Tab key or your mouse to move to another field. The data in the other fields will be updated automatically.

Zone Choice

If you wish to specify a particular zone for the UTM coordinates displayed in one of the panes, choose the zone using this control. The UTM coordinates in the pane will be updated automatically.

By checking the Lock checkbox (see below), you can ensure that this control remains unchanged when you enter new geographic coordinates. This is useful for performing geographic-to-UTM conversions on several points that may normally be considered to lie in different zones.

Hemisphere Choice

The Hemisphere control appears to the right of the Zone control and displays either "N," indicating the Northern hemisphere, or "S," indicating the Southern hemisphere. When entering UTM coordinates, you can change the desired hemisphere with this control.

If this control is changed, the UTM coordinates in the pane will remain unchanged, but the geographic coordinates and the remainder of the data displayed by the tool will be updated.

This control cannot be modified in the read-only output pane. This control is not locked when the Lock checkbox is checked.

Lock Checkbox

By checking this box, you can ensure that the currently selected UTM zone will be used for all UTM coordinates displayed in the pane. You can still change the UTM zone, but the tool will not change the zone itself.

You cannot lock the hemisphere setting.

Datum Select Button

Figure 5.  Datum Select ButtonSelect a new datum for the current pane by choosing this button. A dialog will appear, providing a list from which you can choose a new datum. When you dismiss the dialog by choosing OK, the data displayed in the Coordinate and Datum Transformations tool will be updated.

The currently selected datum is described in the text field below the Select button. If the datum description is too long for the field, you can place the cursor in the field to scroll to the right and read the description.

Performance Issues

This is a list of known performance issues for the Coordinate and Datum Transformations tool.

Java 1.1 Required

This tool requires a Java virtual machine (JVM) that supports Java 1.1 or higher. Some older versions of popular browsers do not support Java 1.1, or do not support it correctly. There is no plan to adapt the tool to run on JVMs that do not support Java 1.1 or higher or to account for the shortcomings of third-party JVMs.

FYI, the reference platforms used to develop the Datum and Coordinate Transformations tool were:

  1. Sun Microsystems Java Development Kit (JDK) 1.3, running on the Windows NT 4.0 platform.

  2. Sun Microsystems Java Development Kit (JDK) 1.3, running on the Red Hat Linux 6.2 platform.

  3. Opera 5.02 (Win32) from Opera Software, with the Sun Java Runtime Environment 1.3.

  4. Netscape Navigator 4.7 (Linux).

Microsoft Internet Explorer Issues

It was observed with an earlier version of this tool that Microsoft Internet Explorer 4.0 (Win32) did not properly support the list box object from which you can choose new geodetic datums. You may be unable to select a new datum when running the tool in the Internet Explorer browser.


Last update: 28 Jun 2001 -- (Copyright) -- (Contact)