Thursday, September 22, 2005

New Coordinate Readout Modes in GTViewer 5.0

GTViewer has always provided two modes for Coordinate Readouts: system mode and computed mode. With GTViewer 5.0, two more modes are provided to display coordinates at latitude and longitude values.

The Coordinate Readout defaults to Computed mode and most users probably never change it. Computed mode displays the coordinate values as they are in their source GIS which is what most users want to see. Computed is probably a misleading label, but the values are “computed” from GTViewer’s internal system coordinates. The System mode will display the coordinate values using the internal coordinate system used by GTViewer and is probably only useful to advanced users working directly with the data.

With GTViewer 5.0, there are two new modes for displaying the coordinates as latitude and longitude regardless of the coordinate system used by the data. One mode displays the coordinates as Decimal Degrees and the other as Degrees/Minutes/Seconds.

The Coordinate Readout setting affects the display and use of all coordinate values in GTViewer:

  • The current position on the cursor is shown on the status bar
  • The Attribute Info Dialog’s Element tab show element coordinates
  • The coordinate labels used on Print borders
  • The interpretation of coordinate values in the Locate XY dialog

There are two requirements before the Latitude/Longitude modes can be used:

  • The GPS Components must be installed for GTViewer
  • The data must have a coordinate system defined using the GPSInfoFile entry in the .GTM file

The Coordinate Readout mode is set either in the .GTM file with the CoordinateReadout entry or with the Options/Settings dialog in GTViewer. The Settings dialog in GTViewer 5.0 now allows the user to set a coordinate system as their personal default, so if the user wants to always use one of the Latitude/Longitude modes, they can set this as their default.

When using either of the Latitude/Longitude modes, the Locate XY command found under the Query menu becomes a Locate Latitude/Longitude command and it will accept either Decimal Degrees or Degrees/Minutes/Seconds as inputs. To use Degrees/Minutes/Seconds, separate the three components with a delimiter (space, comma, colon, or semicolon); there must be three delimited values for both the Lat and Long prompts.

Remember that in the Western Hemisphere, the Longitude value is negative to indicate West. Use a negative value for Latitude to indicate South.

When using the Latitude/Longitude Coordinate readout with Decimal Degrees, you will usually need to increase the Coordinate Readout Precison to 6 or more numbers after the decimal place to get a useful readout. The precision is also set with Options/Settings.

For more information on the Locate XY dialog see the previous Blog posting: Locate XY's Hidden Features

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