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The Benefits of the LMX-200 GPR

This article looks at using simple geolocation and google maps output from the LMX-200 utility location radar and presents a case study on structural monitoring with vibrating wire crack meters, stepping through the decision process to use these sensors and the data logging required. 

Adjusting LMX-200 Google Maps output

The LMX-200 Enhanced Utility Location GPR has a powerful set of geo-location functions when paired with a good GNSS Receiver. This article will look at some output taken with clear satellite line of sight and some techniques to correct for surveys where tree cover or other interference has reduced the accuracy.

GPR-GPS-Sample-LineLine scans collected with the LMX-200 include location information for each segment of the line scan image, this information includes Longitude, latitude and altitude information as received by the LMX-200 controller while scanning.

The quality of this location information is controlled by the quality of the receiver, surveyor quality receivers can be interfaced with the unit where absolute location accuracy is vital. The performance of all receivers is also affected by signal quality, especially with receivers that only use satellite networks where tree cover or tall buildings are a common source of interference. Using the on-screen markup function services can be tagged on any LMX-200-line scan, the image at right shows a portion of a line scan marked with this tool

The Google-Maps image below shows the path of this line scan at the top left and another scan on the lower right. The red dots are the same dots seen on the line scan image and the yellow camera icon shows where the screenshot was taken and also allows someone viewing the results in google maps to bring up the screenshot.

GPR-GPS-Sample-Map

The case study will cover adjusting a raw google maps' output file from the LMX-200 GPR to better represent the real path of the scan and to better present the interpretations.
The image below shows that raw output for a larger project that has been marked using the LMX-200 on screen annotation function.

GPR-GPS-Raw

The GPS path for each scan is shown, every annotation is visible and shows a name based upon the colour used during the on screen markup. As there is tree cover in this area the GPS paths are less clear than those from the first sample.

Corrections will be made to clean up the paths, removing the jumps where the GPS has not correctly tracks. The paths not being discussed will be removed and the markup points will be renamed and coloured.

To remove the path, the Lineset/gps folder in the "places" bar at left is opened and the check boxes un-ticked. Line 12 is kept. To remove annotation not connected to this path we can click on them to select them in the left hand side "places" bar or on the map, and then their boxes unchecked.

GPR-GPS-Single-Line

Second the GPR paths are cleaned, it is important when doing so to only remove mis-tracked points from the line, leaving the correct points in place. Especially important is not to click on clear areas which adds extra points, care here ensures that as much as possible the GPS path is a clean representation of the path the LMX-200 was moved over.

To begin click on the path and select properties, the points on the line are then visible as red squares. Squares are selected with a mouse click and deleted with backspace.

GPR-GPS-Start

Starting at the beginning of the scan it is possible to delete all the points near the intersection and start the path just after leaving the traffic island. This can be achieved by selecting the first point and pressing delete until all desired points are removed.

The next spot with poor tracking has the GPS path shift left and right, to fix jumps away from the true path each such point should be selected and deleted individually

GPR-GPS-Slight

Sometimes the paths recorded are going to be so poor that most of the points are in the wrong locations as in this example.

GPR-GPS-Treecover

it is possible to delete all the points covered by the tree, but is important that either notes taken on site confirm the new path position as correct or that no important utility markings are to be found in this area. Finally it is very important after any edits to select ok in Google's Edit Path window, otherwise the corrections will be undone.

Path corrections made this is already a clearer image, now the annotations can be adjusted.

Closely spaced annotations may overlap, so one can be unchecked in the places bar if required.

GPR-GPS-Nearby-Points

Each point can be renamed, re-coloured or the point's Icon changed from the right click> properties window, it is important not to accidently move them on the map while adjusting their appearance. 

GPR-GPS-Point-Edit

With the editing of the points the cleaned GPS data is complete, where the GPS paths in a scan are not affected by tree or building cover it should only take a moment to rename and adjust points.

GPR-GPS-Final


The two sample data sets in this article both represent good use of the LMX-200's output to google maps, this is only the most basic use of geolocation data with Sensors and Software equipment, Ekko-Project has powerful adjustment, markup and export tools, producing corrected line-scans with real altitude information and exports to .csv or CAD files.

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