Sunday, August 14, 2005

Creating Extract Files (.GTX)

An Extract File, or .GTX file, is a single, self-contained file that can be used with GTViewer, Pocket GTViewer, GTVx, and GTWeb Server. For more information on what Extracted Data is, see the Unextracted versus Extracted Data posting.

There are many different ways to create extract files (.GTX), so many that users may not be aware of them all. This posting will cover each different approach and provide general information on the Extract options.

GTViewer provides two methods for creating extracts. The first method I will describe is probably the most commonly used of all the methods. The Extract Data command found on the toolbar and the menu item under Tools/Extract Data actives the Extract Data mode which allows the user to drag a fence in the current view. This fence is always a rectangle and once placed, the user will see the familiar Extract Data dialog:

This interactive method or performing an extract allows the user to define several settings. The most important item here is the Output File which will specify the file to store the extracted information into. This file is the .GTX file.

The Description field is the name that is associated with the extract. By default, the name is the same as the parent dataset with the “(Extract)” text appended to the end. You can change this description to anything you want and it always appears in the File/Properties information as shown below:

The Filter Preset Support options determine what information will be extracted. If you have Preset Filters defined in your data and you support them in your extract, then all graphics necessary to support the Presets will be extracted. This method will probably include data that is not currently displayed and you may wish to add Presets to make sure that you include all of the data you want in your extract if some features normally default to not be displayed. If you select to extract only Displayed Graphics, then only the graphics currently displayed will be extracted (this does include features that are not currently displayed because of minimum and maximum threshold, but it does not include any features that are explicitly turned off). Extracting only displayed items is a very easy way to reduce the size of the extract, but make sure that you are not going to need a query or tabular information on one of the features that is not displayed since it will not get extracted.

The Data Support options allow the extract to include or not include Attribute Info data and/or Queries. If you choose not to support Attribute Info, you will not be able to review attributes on any feature. If you do not support Queries, then no queries will be available. If you do support Attribute Info and/or Queries, only the records that are associated with the extract area are stored in the extract file.

The Passcode Protection options allow a degree of security to be place on the .GTX file.
A Passcode (up to 10 digits) can be assigned to the .GTX file and every time the file is opened, the user must enter the Passcode to gain access to the file. Two more options are available to provide more control over how the .GTX file is used. The Days before Active setting allows a number of days to be specified. No password will be required until the number of days from the creation date of the extract is greater than the Days before Active value has been reached. This parameter allows .GTX files to have an expiration date, just set the Days before Active to 30, and don’t give out the passcode with the .GTX file. After 30 days, the file becomes useless without the Passcode. The Inactivity Timeout setting allows a time in hours to be specified of allowable inactivity. If the application is inactive for at least this period of time, the Passcode must be re-entered to gain access to the .GTX file again. This setting is designed to prevent unauthorized access for Pocket GTViewer in case the device is lost or stolen. Since the Window CE devices do not close the application when powered off, the file does not get reopened when started up again, so the Inactivity Timeout can provide an extra layer of security.

GTViewer provides a second approach to creating extract files. If you need extracts to have a different shape than a rectangle, you can draw a session graphic (redline) shape around the area you wish to extract. If this shape is selected, the Tools/Extract Data By Shape menu option is enabled and when selected, the standard Extract Data dialog is displayed. This method of extraction can be very useful if you are wanting to create extracts of Circuits whose bounding rectangle is significantly larger than a carefully placed shape around the data. For example, if the circuit is “L” shaped, a rectangular extract will include a significant about of data that does not relate to the circuit; however, a shape around the circuit’s path can considerably reduce the size of the extract.

GTVx supports the same two extract techniques as GTViewer. The ExtractData and ExtractByShape methods are provided to perform these tasks. ExtractData provides the standard rectangular fence extraction and ExtractByShape will use a selected Shape. The same Extract Dialog found in GTViewer is also used by GTVx.

GTWeb provides a command in the Client’s Right Mouse menu to extract the current view. When activated by a client, the GTWeb Server will create a .GTX file for the client’s current view and send it down to the client.

The GTViewer SDK provides an ActiveX control called GTExtractX that is very similar to the GTVx interface, except there is no GUI required and the user has parametric control over all of the settings instead of the Extract Dialog.

Last, but not least, GTData provides the GTPack and GTExtract utility for creating .GTX files. These utilities provide command-line utilities for the creating of extract file. See the previous blog posting for more information on these utilities and their differences.

A few other points about Extract files:
  • You can make extracts from and extract.
  • Currently, an extract file can be up to 2G in size.
  • Extracts always contains a session, but you can create sessions from Extract files.
  • Extract files can be used directly by GTViewer, Pocket GTViewer, GTVx, GTWeb Server, GTRead, GTExtractX, GTPack, GTExtract, Pocket GTReport.
  • Extract files are completely self-contained with the exception of the optionally used TrueType Fonts, Raster files, and external detail files.

No comments: