Thursday, March 24, 2011

Creating a Localization in TopSURV



To set up a survey with localization, tap the Localization button found in the Setup menu:


Localization is used for transforming coordinates between a local system and a WGS84 system. The basic approach of calculating the mathematical conversion is to provide pairs of coordinates for each point used for localization in the job.

The Localization screen contains a list of points used for imagelocalization, called control points. Their coordinates are known in both systems: Known (Local), hand entered or imported ground coordinates, and Meas Pt (WGS84), points measured with GPS. Each point has a level of reliability specified with the values of the residuals along the horizontal (rH) and the vertical axes (rV) and the Control parameters that shows the status of the point. The horizontal and vertical use of any of the control points can be changed by selecting the line and then tapping on the header of the H Control or V Control. This toggles the display between "used" (yes) and "not used" (no).

Adding Localization Points

To perform a localization in TopSURV, there are three simple steps:

1. You Must have the Known (local) coordinates in the TopSURV field job. These known coordinates are usually keyed in or imported from a text file.

If you are going to import or hand enter new points that are on a local coordinate grid it is important to first have the projection set to NONE (this can be done in the Coordinate System Configuration:imageimage

It is also important to set the Coordinate Type to GROUND in the Display Configuration:


Also, be sure that the UNITS are set properly for the coordinates in the Units Configuration:


To enter points by manual input use the Edit Points menu. Enter coordinate values by selecting image


2. Physically occupy and measure the existing control points (brass caps, rebar, nails, etc) in the field with your GPS receiver. These control points must have “known” coordinates. It is recommended that these points be collected with an increased epoch count.


3. Pair up the Known coordinates (Local) and the points of the Measured control (WGS84) in the localization menu.


The Add Localization Point screen contains the coordinates of the control points:


• The Known (Local) Point Field contains the name and coordinates of the point in the known coordinate system.

Select the first Known (local) point using the list iconimage .

imageUse Horizontal: set if the point should be used for horizontal

Use Vertical: set if the point should be used for vertical localization.

• The Measured Point (WGS84) field contains the name and global coordinates of the control points.

Select the first Measured (WGS84) point using the list icon image.

• OK imagesaves the point and opens the Localization screen to display a new point.

Since the WGS84 points were previously measured there is no need to take a new measurement or use the measure button image.

Continue to Add control points until you are satisfied with your residuals.


• Remember a general rule of thumb: Always Use 1, 4, or more good control points for a localization.

1 point - is generally good for small projects (1 mile radius or less)

4 points or more - it is always best have your controlling points surround or envelope the worksite. Many surveyors will run a differential level loop through the control points prior to the localization, ensuring a good vertical control.

• Always try to leave a known control point or two out of the localization to use for checks when possible.

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