Global Mapper: A Surveyor’s Perspective

By V. Kelly Bellis

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It all began innocently enough. For Christmas, my wife gave me a Garmin Oregon 550 and I just needed to get some raster images onto this hand-held GPS device. Global Mapper did the job without much ado. That was six years ago.


Background map created by Global Mapper as seen above on the Triumph-LS receiver manufactured by Javad GNSS.

Next came the LiDAR data for our area and with its availability in the late summer of 2011, Global Mapper rocked since it could read native LAS files, again without any fuss. Of course all the really cool stuff you could do with LiDAR data; e.g., surface modeling, contour generation, watershed studies and so forth was also available in Global Mapper. That’s when in earnest I began digging deeper into the program.


Georeferenced old lotting plan on Swans Island rectified using Global Mapper with calculated waypoints overlaid for field reconnaissance.

Today, Global Mapper has become a critical part of all aspects of any given surveying project’s workflow in our office. From the prospective client’s first inquiring telephone call, loading up tax maps and aerial imagery, creating way points for reconnaissance to more sophisticated analysis for optimal UHF antenna placement, Global Mapper’s day-to-day role has only increased. It has also become quite useful in many other spatially related analytics and 3D visualizations. Global Mapper is more than just a mapping tool for the surveyor; it’s a bridge between realities.


Map of Maine showing existing and proposed CORS for a discussion on the future of RTN in Maine held during the 2014 Fall Meeting of the Maine Society of Land Surveyors. All spatial content developed in Global Mapper with final assembly of the poster using InDesign.

While Global Mapper isn’t the only tool in my tool box and other software applications will typically be employed in the production of most deliverables, it’s role in producing those work products increases as does my reliance on Global Mapper. It’s developers, Blue Marble Geographics (BMG), a Maine-based company continues to offer exemplary support and has demonstrated keen interest in the feature sets which grow with each update. In addition to the support offered directly from BMG, Paul Tocknell maintains http://www.globalmapperforum.com/ where over 36,000 registered users seek and give peer-to-peer assistance and advice. It’s an incredible resource.

Having done land surveying since 1975, I’ve witnessed several changes in how we work. Many of these changes are integrally tied to technology’s advance and at the top of the list of significant developments during that 40-year period is unquestionably the developments linked with Global Navigational Satellite System (GNSS) surveying.

It is also during this time span where the land surveyor whose feet, once firmly planted on a single planar surface in an assumed coordinate system, have come to accept that their origins of say, 5000x, 5000y, have transcended to the center of the Earth, and their feet that were once considered as being planted over a stationary position on that surface, is in fact, spatially transitory. Date stamps have acquired greater notice as a result with Horizontal Time Dependent Positions (HTDP).

This is where once again Global Mapper is able to effortlessly bridge a mindset once pinned to a flat plane and allow the surveyor to begin wrapping his head around the ellipsoid. The once aloof science of geodesy becomes approachable for the average land surveyor thanks to the incredible set of tools logically arranged inside of Global Mapper.


Relief map of North America showing progress of  NGS’s GRAV-D program (circa 2012). All spatial content developed in Global Mapper with final assembly of the cover illustration using Photoshop.

NGS’s forthcoming purely gravimetric height system[1] will reshape many aspects of our lives by impacting engineering, mapping, flood risk analysis, transportation, land use, ecosystem management and eventually, even our laws. To better understand this subject, and one of the most fun and fascinating projects that I’ve ever worked on, Global Mapper was pivotal throughout the effort. It greatly facilitated my study of gravity, particularly, visualizations of the geoid, ultimately culminating in the two-part series; Gravity’s Increasing Gravitas[2] and the Geoid gallery[3].


The geoid is the surface on which no marble will roll on its own accord.

Visualizing any equipotential surface, much less that surface covering the Earth and determined exclusively by gravity, seemed daunting to me, at least at first. As it turns out, in some ways its not any different than regular topographic surveys we prepare; a mess of points tied to a vertical datum scattered about the x and y axis. Instead of that vertical datum being tidal or terrestrial, its ellipsoidal. And the data: is free, plentiful, and Global Mapper reads it in without much fanfare like any other ASCII file. From there, it’s just business as usual; grid and TIN it, and there’s your surface.

Thanks to NGS and the GRAV-D program, land surveyors in the United States will be able to determine orthometric heights to within 1 to 2 cm anywhere in the country when the new height system is fully implemented. And thanks to Global Mapper, surveyors will be able to transition their work as needed using its existing toolset. In addition, BMG ‘s Geographic Calculator can presently be conjoined with Global Mapper making it even more powerful in coping with the ever migrating tectonic plates and the associated importance of Horizontal Time Dependent Positions.


Map of the northeasternmost flight coverage and airborne gravity survey conducted by the NGS and its GRAV-D program. All spatial content developed in Global Mapper with final assembly of the illustration using Photoshop.

In summary, and if the surveyor reading this is to take away anything, it is my hope that they’ll keep these two items in mind: 1) Global Mapper is an indispensable tool that should be in their surveying tool kit and 2) a new national spatial reference system is coming soon; get ready.

A Glimpse at the Geoid Gallery

All rendered images of the geoid shown are predicated upon the data generated by GFZ Potsdam and in particular, the combined model EIGEN6C, using GFZ’s online calculation service. This particular model (EIGEN6C) combines GOCE data plus other data from altimetry and terrestrial sources.

The geoid’s basic spherical shape was defined using a grid step interval of 0.1° in both latitude (φ, phi) and longitude (λ, lambda) resulting in 6,485,401 grid points for the entire surface. In other illustrations zoomed in at closer levels, the gridstep intervals were even closer, the values of which are indicated on each illustration.

Many thanks to the amazing online services provided by the GFZ German Research Centre for Geosciences at the Helmholtz Centre Potsdam and to Franz Barthelmes for his kind support.

All spatial content and its associated mapping in these illustrations of the geoid was done using Global Mapper. Many thanks go out to Mike Childs of Blue Marble Geographics for his tremendous support.

Because the surface of the geoid is fairly complex, no single light source satisfactorily illuminated the subject. To improve the overall illumination, multiple renderings (varies between 3 and 5) of the exact scene were done using different lighting azimuths and altitudes and then combined using Oloneo’s incredible Relight module in Photo Engine which allowed each lighted scene to be dimmed or brightened independently of each other to achieve the desired effect. Additional graphic embellishments (curves, toning, etc.) were done using Photoshop.


Africa to Australia
Geoid model: EIGEN6C, Gridstep: 0.1°
Filter type: Gaussian, halfresponse, Filter length: 0.1°
Projection: Mercator, Graticule interval: 12°


Aleutian Trench
Geoid model: EIGEN6C, Gridstep: 0.03°
Filter type: Gaussian, halfresponse, Filter length: 0.1°
Projection: Mercator, Graticule interval: 3°


The Americas
Geoid model: EIGEN6C, Gridstep: 0.1°
Filter type: Gaussian, halfresponse, Filter length: 0.1°
Projection: Geographic, Graticule interval: 12°


Diving Laccadive Sea
Geoid model: EIGEN6C, Gridstep: 0.02°
Filter type: Gaussian, halfresponse, Filter length: 0.05°
Projection: Geographic, Graticule interval: 5°


Equatorial Slice
Geoid model: EIGEN6C, Gridstep: 0.03°
Filter type: Gaussian, halfresponse, Filter length: 0.05°
Projection: Geographic, Graticule interval: 12°


Entire planet
Geoid model: EIGEN6C, Gridstep: 0.1°
Filter type: Gaussian, halfresponse, Filter length: 0.1°
Projection: Geographic, Graticule interval: 12°


Entire planet
Geoid model: EIGEN6C, Gridstep: 0.1°
Filter type: Gaussian, halfresponse, Filter length: 5°
Projection: Geographic, Graticule interval: 12°


The Gulf of Maine
Geoid model: EIGEN6C, Gridstep: 0.01°
Filter type: Gaussian, halfresponse, Filter length: 0.1°
Projection: Mercator, Graticule interval: 1°


Indian and Pacific Oceans
Geoid model: EIGEN6C, Gridstep: 0.1°
Filter type: Gaussian, halfresponse, Filter length: 0.1°
Projection: Geographic, Graticule interval: 12°


Izu Bonin Mariana Arc
Geoid model: EIGEN6C, Gridstep: 0.02°
Filter type: Gaussian, halfresponse, Filter length: 0.1°
Projection: Geographic, Graticule interval: 3°


North America
Geoid model: EIGEN6C, Gridstep: 0.06°
Filter type: Gaussian, halfresponse, Filter length: 0.1°
Projection: Mercator, Graticule interval: 12°


Western North America
Geoid model: EIGEN6C, Gridstep: 0.1°
Filter type: Gaussian, halfresponse, Filter length: 0.1°
Projection: Albers Conic, Graticule interval: 12°


Hypsometric Tints Only – No Hill Shading
The above illustration uses only color to depict the height of the geoid in its relationship to the ellipsoid - see elevation legend below for all illustrations in the Geoid Gallery.

Actual elevations of the geoid’s surface as measured in meters and relative to the WGS84 ellipsoid have been multiplied by a factor of 10 to the 5th power in order to help visualize its shape. Additionally, Global Mapper has used an added multiplier of 3.

The hypsometric tints have been developed exclusively for these geoid illustrations with a narrowly defined red band at zero - representing its intersection with the ellipsoid. Custom shaders are just one more cool feature offered in Global Mapper.

 

Press Release update: http://www.directionsmag.com/pressreleases/global-mapper-version-16.2-now-available-with-improved-3d-viewer-upgraded-f/443600

 

 



[1]
   By 2022, the United States will transition to an entirely new height system as outlined in “National Height Modernization Strategic Plan NOAA’s National Geodetic Survey (NGS) December 2012”; http://www.ngs.noaa.gov/web/surveys/heightmod/HMODPlanApprovedDec2012.pdf

[2]    Part One and Part Two of Gravity’s Increasing gravitas are available in their originally intended format at http://panocea.us/gravitys-increasing-gravitas/ 

[3]    All images created for the Geoid Gallery are available at http://panocea.us/geoid-gallery/

 


Published Wednesday, May 20th, 2015

Written by V. Kelly Bellis



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