May 25, 2021

Updating Outdated Survey Control Points Using a Variety of Blue Marble’s Applications

Written by: Jeff Hatzel

 

Geospatial projects often require the use of a variety of tools and software applications. These tools can span desktop, web, and mobile platforms. Using tools that collaborate across different platforms allows for tasks to be completed more efficiently and with increased flexibility. 

In this blog, we look at a field user who needed to update survey control points that have not been visited or had their survey updated in a long time. In order to accomplish this, the points’ coordinates needed to be updated to match current survey standards, added to a map and sent to Global Mapper Mobile Pro to find and update those points in the field.

Using the Point to Point Converter in GeoCalc Online

The two points in question were last surveyed in reference to NAD 27. The current GNSS survey equipment in use will reference the latest WGS 84 (G1762) / ITRF. Since these points have not physically been visited in a long time, the user needed to ensure they had the most accurate coordinates possible when out in the field to make it easier to find the old markers. This would entail a two-step transformation process, first from NAD 27 to NAD 83 (1986), followed by a time-dependent transformation to WGS 84 (G1762).

Although this user was away from the office and did not have access to their desktop installation of Geographic Calculator, they were able to use the new Point to Point Converter on GeoCalc Online, which supports Horizontal Time-Dependent Positioning (HTDP) transformations.

A HTDP transformation from NAD 83 (1986) to WGS84 (G1762) is performed for the second control point, prior to adding it to Global Mapper.

Adding Control Points to and Existing Map in Global Mapper

Working simultaneously in GeoCalc Online and Global Mapper, it was easy to create points from the calculated coordinates in GeoCalc Online. Using Global Mapper’s Point at Position tool, it was as simple as copying and pasting the calculated values into an existing Global Mapper workspace, which has some reference data.

The Point at Position tool in Global Mapper is used to add the second control point to the first in the existing workspace.

The completed workspace also contained a feature template layer. This layer does not contain any data at this stage, but will be used in the field to ensure proper attribute information is recorded for the updated points. This file is now ready to be exported from Global Mapper as a Global Mapper Mobile Package (GMMP) file.

Ready for export to GMMP, the final map contains the two points calculated using GeoCalc Online, some reference tax parcel data, and a feature template layer.

Updating the Control Points in the Field

For the work in the field, this user utilized the Pro Module of Global Mapper Mobile. Once their map was loaded, they chose to connect to an external GPS unit using the Advanced GPS functionality available to Pro Module users. This is referenced in the Location Information on their display.

When connected to an external GPS using the Advanced GPS functionality that information is always reflected in the Location Information. Further details can be found in the Menu under Advanced GPS.

With the location information ready to go, selecting one of the points allowed the use of the Distance and Bearing tool, a Pro Module feature, to determine where they were in relation to the selected point. They could then navigate with live updates as they moved in the field to help find the old survey control marker. Given that these had not been surveyed in a long time, the initial transformation steps allowed this user to have as close of an idea as possible as to where they needed to go to find these markers. Once found, the user was able to create a new point at the location in Global Mapper Mobile, recording the location information from their external GPS unit and adding any required attributes as specified by the feature template layer. This process was then repeated for any additional points.

Creating the point based on GPS location allows that point to retain location information sent to Global Mapper Mobile from the external device. 

Once these points were updated, the user was able to save and export their work from Global Mapper Mobile, sending it back to the office for further analysis. Using a variety of Blue Marble’s software applications the update of these survey control points was  conducted efficiently and accurately.

Learn more about Global Mapper, Global Mapper Mobile Pro, Geographic Calculator, and GeoCalc Online by visiting our website at www.bluemarblegeo.com. Trials of all products are available for download.  For further information, please contact our sales representatives at info@bluemarblegeo.com

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