The GPS Tracklog
The GPS Tracklog in ArcPad is stored in a shapefile format. The GPS Tracklog can be started or activated when the GPS is active. ArcPad automatically records each GPS position it receives as a point feature in the GPS Tracklog shapefile, as long as the GPS Tracklog is running and the GPS is active. The GPS Tracklog is an electronic breadcrumb trail that shows the path that you have traveled. ArcPad uniquely displays these GPS positions, or points, in the tracklog as a red line.
The GPS Tracklog points are always captured in latitude and longitude degrees using the WGS84 datum. ArcPad automatically projects the tracklog points using the projection of the current ArcPad map when displaying the tracklog. Although ArcPad treats the GPS Tracklog point shapefile in a unique way, the tracklog is still a standard PointZM shapefile that can be used in the same way as other PointZM shapefiles. The Tracklog shapefile can be added to an ArcPad map by using the Add Layer(s) dialog box.
When adding the tracklog shapefile with the Add Layer tool, ArcPad treats the shapefile as a standard point shapefile. ArcPad displays the points as points and does not perform on-the-fly projection of the tracklog’s point data—which is in latitude and longitude degrees using the WGS84 datum.
For each point in the tracklog shapefile, ArcPad captures an x, y, and z coordinate with a user-specified m value. ArcPad also captures a variety of information received from the GPS receiver and stores this information in the attributes associated with the point. These attributes can be viewed by using the Add Layer tool to add the tracklog shapefile to an ArcPad map and then by using the Identify tool to display the selected point’s attributes.
The GPS information captured for each point in the tracklog, and the associated field, is as follows:
LATITUDE: Latitude in the datum of the GPS receiver
LONGITUDE: Longitude in the datum of the GPS receiver
ALTITUDE: Altitude in the datum of the GPS receiver (in meters)
EASTING: UTM easting
NORTHING: UTM northing
UTCDATE: UTC date
UTCTIME: UTC time
SOG: Speed over ground (in km/h)
COG_TRUE: True Course Over Ground (in decimal degrees)
COG_MAG: Magnetic Course Over Ground (in decimal degrees)
SATS_USED: Number of satellites used
HPE: Horizontal position error (in meters) (only when using a Garmin GPS receiver)
VPE: Vertical position error (in meters) (only when using a Garmin GPS receiver)
EPE: Estimated position error (in meters) (only when using a Garmin GPS receiver)
HDOP: Horizontal Dilution of Precision
VDOP: Vertical Dilution of Precision
PDOP: Position Dilution of Precision
QUALITY: GPS fix quality, where:
0 represents no fix.
1 represents GPS or SPS (Standard Positioning Service) fix.
2 represents DGPS (Differential GPS) fix.
3 represents PPS (Precise Positioning Service) fix.
DIFF_AGE: Age of DGPS fix (in seconds)
DIFF_ID: ID of DGPS station used
DEPTH : Depth (in meters)
DEPTH_OFF: Depth offset (in meters)
WATERTEMP: Water temperature (in degrees Celsius)
The size of the GPS Tracklog shapefile’s dBASE® table can get fairly large if the Tracklog is active for a long period of time. You can reduce the size by deleting fields from the tracklog shapefile’s dBASE (*.dbf) table. You can use ArcGIS Desktop (ArcView, ArcEditor, or ArcInfo) to delete fields in the shapefile’s dBASE table.
The x, y, and z coordinates, together with the m value, can be viewed by using the Geography tab of the point feature’s properties.
The GPS Tracklog points can be captured simultaneously while using the incoming GPS positions to capture other point, line, or polygon features. Consequently, the GPS Tracklog captures points independently from the ArcPad editing tools.
The GPS Tracklog layer is always displayed as the first layer on the Layers page of the Table of Contents.
The GPS Tracklog layer can be displayed, or made visible, whether the GPS is active or not. The GPS Tracklog has its own set of unique properties, which can be displayed by using the Layer Properties button in the Table of Contents.
Using these properties you can:
- Change the name and location of the Tracklog shapefile.
- View the number of GPS positions or points in the tracklog.
- Clear or delete all of the points in the tracklog.
- Specify the interval to be used by ArcPad when recording the GPS positions in the tracklog. An interval of 2, for example, means that ArcPad will only use every second incoming GPS position to record a tracklog point.
- Specify whether or not ArcPad must use the GPS Quality rules when capturing points in the Tracklog. The GPS Quality rules are specified on the Quality page of the GPS Preferences dialog box.
- Select which GPS information ArcPad must use to store in the tracklog point’s measure value. Available options are PDOP, HDOP, VDOP, TDOP, EPE, HPE, VPE, TIME, DEPTH, and SOG.
Any changes to the tracklog properties only take effect the next time the tracklog is started. Changes do not take effect if the tracklog is currently running.