Working With Google Earth

In order to be able to output data from TBC to Google Earth, the TBC project needs to be “coordinated” so that the data in the project can be output to Google Earth in KML/KMZ format as Latitude, Longitude, Height in WGS84 Reference System.

In order to achieve that you can do one of the following

  1. If you have a Site Calibration file for the project (.DC, .CAL, .CFG, .JXL, .JOB) from Trimble SCS900, Siteworks, Access, GCS900 or Earthworks you can drag and drop the file into the TBC project and that will set up the coordinate system for you

  2. If you have the Coordinate System information for the project e.g. US State Plane, NAD 83, Texas South Central Zone with or without Geoid information then you can set that up in the TBC Change Coordinate System command. This will establish the TBC Project Settings for Coordinate System (Projection, Datum, Zone, Shift / Projection / Snake Grid etc.)

Both Google Earth and Trimble Business Center Background Map Services are using Grid Coordinates. If the project data that is provided using Ground then you will find that the TBC Project Data will not match the Background Image or Google Earth imagery after an export. If this is the case then you have two options

  1. On export to Google Earth, you can apply a Northing and Easting shift to the published data to move the published data to the correct position in Google Earth. Those shifts can be determined using the Measure command in TBC to measure from the Image Location to the Actual Location, this will report the N,E values for the two locations. Compute the difference in N and difference in E values and those are your your shifts.

  2. Before export to Google Earth, you can use the Local Site Settings command and enter those same shifts into the False Northing and False Easting offset fields. These will adjust the background Map in TBC so that it fits the data. The same shift is applied to data exported to Google Earth resulting in fit of the data to the Google Earth imagery.

The shifts can also be computed if you know the scale factor between Grid and Ground at the location you are working at. The scale factor can also be determined using the Local Site Settings command in TBC. Remember though that when working with large coordinate values e.g. 8.3 format, that a scale factor of 1.00013 is not accurate enough to determine that precisely - you will need full precision values to compute the shifts - TBC will compute that for you to the accuracy required. It is not uncommon to see data that is not accurate enough on the plans so be careful what you use. To compute the Grid coordinate for a known N,E,Z position simply divide the N and E values by the scale factor. The difference between the Grid coordinate and the Ground Coordinate is the shift that you need to apply in the Local Site Settings command.

For small to medium size projects, typically you can assume that the scale factor is constant over the entire job. You should determine the scale factor somewhere near the center of the job to minimize the scale factor effect. On long linear projects the scale factor will likely vary and you may need to break the job up into sections rather than treat it as one for the overlays to match up correctly.

Once you have the coordinate system setup correctly if you turn on the background image service in TBC, you should find that your linework matches the imagery / street maps pretty closely. If that is the case then exporting to Google Earth should result in the same level of matchup.

Note: If you have the background Map Service turned on, and you change the Local Site Settings, you will find that the Map Data will not move. To force a recompute do the following

First go to Project Explorer, at the top select the Project Name
In the properties pane - you will see the dialog group called Background Map and the option called Type - select the other option to what is currently selected i.e. if Trimble Mapview is selected then select the Digital Globe Imagery option and vice versa if the Digital Globe Imagery option is selected. This will force the Map system to regenerate and in that process it will appear in the shifted location based on the entries made in the Local Site Settings command. You can change it back once the graphics has regenerated. Note that simply switching the Background Imagery Off and On again does not have the same effect.

The video explains the process

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