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GPS

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Openwind can make use of any GPS that communicates using NMEA sentences and can be connected via a serial port or, in the case of Bluetooth devices, a virtual serial port. Figure 165 illustrates the Connection tab of the GPS dialog.

 

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Figure 165:   GPS Connection Tab

 

 

The port number is the serial communications port number. On a PC, the first com port is usually called com1. Figure 165 shows Openwind connected to a USB GPS appearing as com4 in the device manager in Windows control panel. The baud rate specified in the dialog appears to have little effect so long as the port number is correct.

 

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Figure 166:  USB GPS in Device Manager

 

 

 

The best way to know that your GPS is correctly connected and communicating with Openwind is to note the flow of text through the NMEA Sentence window at the bottom of the Connection tab. The time reported in the Connection tab is GMT and should be correct as long as the GPS can see one or more satellites.

In general, a GPS needs to see at least four satellites before it can give a fix on a user's position.

 

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Figure 167:   GPS Position Tab

 

 

The Position tab in Figure 167 shows the current location of the user in both geographic and UTM coordinates. (Support for other projections is planned.) The estimated altitude is also given based on information coming from the GPS.

Assuming that the map-view includes the current GPS location, the current location will be marked on the map-view as OPENWI~1_img189.

Figure 168 shows the Tracking tab of the GPS dialog. When the user checks the box to “Turn On Tracking,” Openwind begins adding points to whichever LineLayer or PointLayer is currently selected in the drop-down list.

It is only possible to add points to a layer that is not the child of any other layer, so this drop-down list only shows layers which are direct children of the workspace.

 

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Figure 168:   GPS Tacking Tab

 

Openwind only adds a new tracking point when the current position moves to be at least the specified distance from the last tracking point. The accuracy of the current position can be gauged by watching how far the current position strays from the last tracking point when stationary.

The GPS dialog is modeless and so can be left visible while work continues in the Openwind interface.

A USB GPS with 5m accuracy can be ordered online for around $35 or less. These are great for getting up and running and for site visits that do not require 1m accuracy.

When either the GPS is connected or the PC is designated a Field PC in preferences, several other buttons become visible. The functions of these buttons are explained in GPS Menu Section.

 

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