Thursday, June 16, 2005

Current View Extents Dialog in GTViewer

Another useful tool in GTViewer is the Current View Extents Dialog. This tool is found under the View menu and can provide some useful information. The job this dialog performs is very simple. It provides the coordinate range of the active view.

Most of the controls on this dialog are for formatting the range coordinate values.

You can select between Computed and System coordinates. For those who do not know the difference, Computed coordinates are the same are your data’s original coordinate system (whatever that may be). System coordinates are the values actually stored in the GTViewer format. Computed Coordinates are called “computed” because GTViewer runs the System coordinates through a computation to get the Computed values. You may ask why you would ever need the range in System coordinate values. Some of the parameters in the .gtm file and some of the data conversion utilities require System coordinates rather than Computed coordinates. Most of the methods used in development use either System or Computed, but there are some that do require system coordinates.

The range output is always specified as XLOW, YLOW, XHIGH, YHIGH; however, you can select the delimiter and and the number of digits shown after the decimal point.

The Copy button will take the text in the output box and copy it to the Windows Clipboard.

To see how this can be used, set the view as you like it and activate the Current View Extents dialog. Select System Coordinates and the Pipe Delimiter. Then Copy the result to the clipboard. In your .GTM file, you can paste the copied text in as the value for the Range entry:

[General Info]

When you open the .GTM file again, it will fit the data to these coordinates. This task is often performed when setting up data for the first time.

The GTExtract utility can also take a range as a parameter which can be obtained from the Current View Extents dialog. GTExtract will use either System or Computed coordinates (depending on the flag you use) and the coordinates are separated by a space delimiter.

You can also paste the range into the Locate XY dialog discussed in a previous Blog entry to locate on a particular range.

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