MicroStation contains an interface to Global Positioning System (GPS) devices. The Global Positioning System consists of a constellation of satellites in earth orbit that broadcast radionavigation signals from which GPS devices can calculate reliable positions on a cost-free, continuous, worldwide basis. Please refer to http://www.gps.gov/ for more information.
MicroStation recognizes GPS devices that connect using serial protocol and send the NMEA (National Marine Electronics Association) standard strings that indicate position, heading, velocity, time, fix type and fix quality. Some such devices connect to the computer using a standard serial cable attached to a serial port on your computer. Others connect using the BluetoothTM protocol that creates a virtual serial port that programs such as MicroStation can read from. GPS devices that support the NMEA standard range from inexpensive consumer units up through very sophisticated surveying instruments. Devices that have been tested include the Garmin GPS 10X Wireless Bluetooth receiver, the Wintec WBT-100 Bluetooth GPS receiver, and the GlobalSat BT-359 Bluetooth Navigation Receiver, but there are many more available. If you are using a Bluetooth device, you should follow the directions that came with the device to get it communicating through Bluetooth, and note the virtual COM port that it uses (e.g., COM 8). MicroStation also supports the GarminTM USB devices that use Garmin's proprietary protocol, such as the GPS 18 USB. That can be plugged into any GPS port, and the supporting software will be loaded by Windows "Plug-n-Play" protocol.
With the GPS device connected and powered up, open MicroStation's Global Positioning System dialog by clicking on the second icon in the Geographic toolbox:
Opening the dialog may take a few seconds while MicroStation attempts to open the specified serial port and find the GPS device. Once open, the Global Positioning System dialog includes a toolbar along the top, and three tabs.
The rightmost icon indicates the status of the GPS connection. It is green if MicroStation was able to connect to the GPS device and has received a valid report from the device within the last 2 seconds; otherwise it is red.
The leftmost icon turns on and off the GPS Tracking mode. Tracking displays the specified cell at the geographic location within the current model. Since the location within the model can be determined only if there is a Geographic Coordinate System assigned, the tool is disabled if there is no GCS. See Section 8.3.3 below for a discussion of the Track Settings.
The second icon from the left turns on GPS Trailing. Trailing places a line string along the track of the GPS device as it moves. See Section 8.3.4 for a description of the Trailing
The third icon sends a data point to MicroStation at the current GPS position.
The fourth icon centers the current view at the current GPS position.
Note: The trailing, data point entry, and view centering operations require GPS Tracking to be turned on, so the icon is disabled it is not.
The first tab contains settings needed by the Global Positioning System interface.
The Device Type field allows selection of either NMEA-Compatible or Garmin USB
When the Device Type is set to NMEA-Compatible, you can select either "Serial Port" or "File Playback" as the source. The Serial Port setting is used when you have a live GPS device connected to your computer. The File Playback setting is used when you have previously recorded an NMEA-compatible GPS session using the GPSRecord program that is described in Section 8.6 below.
When the Source is set to Serial Port, the Comm Port Number and Baud Rate fields let you specify the serial port that the GPS is connected to and the Baud rate. For Bluetooth devices, you must set the COM port that the Bluetooth software tells you it is using for the virtual serial port, and the Baud Rate does not matter.
If the Source is set to File Playback, the Playback File and Playback Speed fields allow you to select the GPS recording file and the speed at which you would like MicroStation to play it back, with 1.0 indicating playing it back at the same speed as it was recorded.
When the Device Type is set to Garmin USB, the Source field allows you to specify "USB Device" or "File Playback" as the source. USB Device is chosen when there's a live GPS device connected to your computer The File Playback setting is used when you have previously recorded a Garmin USB GPS using the GPSRecord program that is described in Section 8.6 below.
Playback File and Playback Speed are described in Section 8.3.2
When GPS Track mode is started, MicroStation looks for the cell that you want it to use to track the current position. The cell name is specified in the Tracking Cell field in the Track Settings section of the Settings tab. If the Cell Library field is not empty, MicroStation looks in the specified cell library; otherwise, it looks in ustation.dgnlib. If the cell isn't specified or can't be found, an alert box is displayed and tracking is not started.
The scale of the tracking cell is set by the Scale field. When Scale is set to 1, the tracking cell is displayed at actual size. When your view scale is small (i.e., when you are viewing a large area), you might want to set the Scale larger to make the GPS Tracking cell easier to see.
The elevation at which the tracking cell is displayed is controlled by the Elevation Source field. In a 2D model, the only option is "Zero". In a 3D model, the other possibilities are "Fixed", in which case an additional field labeled Elevation allows you to enter the elevation, and "From GPS" in which case the elevation is taken from the GPS device.
When GPS Trailing is turned on, the lifetime of the generated trail is specified in the Trail Persistence field. The possibilities are "While On", which erases the GPS trail as soon as trailing is turned off; "Session" which keeps the trail until you either exit MicroStation or view a different model; and "Permanent", which writes the trail as a line string to the active model.
As the GPS position changes, MicroStation adds points to the trail as determined by the three fields Distance Tolerance, Angle Tolerance, and Area Tolerance. The units of Distance Tolerance are the master units of the active model. As soon as the current GPS position is further than the Distance Tolerance from the previously saved point, a point is saved. The of Angle Tolerance is entered in degrees. If the angle formed by the current GPS position and the two preceding GPS position readings exceeds the angle tolerance, a point is saved at the previous GPS position (the vertex of the angle). The units of Area Tolerance are square master units. When the area formed by a triangle consisting of the vertexes of the current position, and the last two positions saved exceeds the area tolerance, the current position is saved to the trail.
If the Show Reason Setting is set to Yes, MicroStation shows the criteria that caused each GPS trail points to be accepted in MicroStation's Status bar.
The Status tab page gives a graphical representation of the GPS satellites that are within reception range, their sky position, and signal strength. The satellites that are drawn in green are being used in the GPS position correction, while the ones in yellow are not. The satellite numbers are assigned by the US Government. 1 through 32 are primary GPS satellites and 33 through 51 are WAAS (Wide Area Augmentation System) satellites that transmit corrections calculated by ground-based receiver stations. The bottom panel shows the raw NMEA strings that are received from the GPS device. It is useful mostly for diagnostic purposes.
The Position tab page shows the position that the GPS device is calculating from the signals that it receives. Most of the field names are self explanatory. The Fix Type is either Autonomous, which is calculated solely from the GPS navigation satellites; Differential, which means that the fix was calculated using either WAAS or a ground-based differential technique; Estimated, which means that the GPS device does not have a fix but is estimating the fix based on some other information; or Simulated, which means the GPS device is simulating GPS signal reception.
The "Dilution of Precision" numbers give an indication of confidence in the GPS position. Lower numbers mean that the position is more accurate. Unfortunately, it is not possible for MicroStation to calculate an absolute value of expected error from these numbers. Some of the GPS vendors have algorithms for doing so, but they are considered proprietary.
The X, Y, and Z fields are shown only if the active model has an associated Geographic Coordinate System.
On occasion, it is desirable to capture a ground track from a GPS device, but not practical to have a live MicroStation session while doing so. To accomplish that, MicroStation provides a separate executable called GPSRecord. The program calculates not just the sequence of positions, but all of the data that the GPS device transmits to client programs. That data is stored to a file for later playback in MicroStation as discussed in Section 8.3.2 and 8.3.3.