This article brought to you by Laser Tech.
Technology is influencing our world to become a more efficient, safe, and precise environment. GNSS/GPS technology is an integral part of recording where on earth something is positioned.
GNSS receivers are powerful mapping tools, and there are times when even the best tools have limitations. Receivers compute the location of their antennas, which requires you to physically occupy a location to accurately map it as a feature.
Physically occupying a location is not always safe or practical.
For instance, in a scenario where you need to position features located on private and residential properties. It may be difficult to gain permission from a property-owner and trespassing without permission leaves you vulnerable to lawsuits and other environmental dangers. Similarly, positioning a manhole in the middle of the street carries an increased risk of being harmed by non-alert drivers, or becoming a distraction that leads to a crash.
On top of this, your access to satellite signals is not guaranteed. Obstructions of a satellite signal can be caused by trees, steep terrain, high-rise buildings, and much more. If you find your signal dropping in and out, you are probably stuck in a GNSS impaired environment. You might be surprised by the number of objects that create this issue. Many professionals have had to find out through trial and error.
Question: What do you do when a GPS/GNSS antenna alone isn’t enough?
Answer: Use a LaserGIS® workflow: using laser offset measurements to remotely capture any feature’s position in areas where GPS/GNSS signal is blocked.
Offsets: Making the Job Easier and Safer
Reduce the time and risk involved in gathering field data with laser offsets.
Integrate a laser rangefinder and an electronic compass (providing distance, inclination, and azimuth) with your GIS data collection system to eliminate the need to physically occupy every point.
This alternative also allows you to measure distance-offsets to features in challenging locations, by recording both a GPS position and an associated distance/direction to the object of interest.
Examples of Laser Offset Mapping Applications:
- Objects located in steep terrain
- Safe recording of data near busy highways
- Manholes and other features located in the middle of the street
- When the GNSS signal is blocked by buildings or trees
- Features which are on private property
Three Laser Offset GNSS Mapping Methods:
1) Range/Azimuth
The easiest way to position remote objects is by measuring the Range (or distance) and Azimuth (or compass bearing) to the target with a laser rangefinder.
This workflow only asks you to stand at a convenient location, accept the default coordinates, and start mapping.
Consider a case where you know the XY location of your starting point, and you want the mapping data to line up to North and overlay onto an existing map. To start, GPS/GNSS can tell you where you are on the map. Then, use a laser rangefinder to start LaserGIS offset mapping.
In the example pictured above, the safe position on the sidewalk is recorded as your known location via GPS/GNSS. You then measure Range - Azimuth to the manhole cover in the street.
This measured data is used to calculate the coordinate of the remote point. You can then take any other offset measurements needed before moving on to your next area.
2) Range/Angle
The Range-Angle method is very similar to the Range-Azimuth method. The difference comes down to measuring horizontal angles from an encoder to produce the direction to your target.
This method offers a solution for anyone forced to stand and position assets in areas that have magnetic interferences to a compass.
The Range-Angle method can be used to generate relative coordinates for many great solutions, like Area and Volume, where you’re not concerned with aligning the map to North or comparing it with GPS/GNSS data.
When making use of GPS/GNSS to geo-reference your data, you can take a single-shot laser offset from your known GPS location to generate the coordinates of your remote target. For this method, you will need an extra one-time shot to the Reference Point that is already logged with your GPS equipment.
In the example pictured above, the reference point’s location is already logged. The safe position on the sidewalk is recorded via GPS/GNSS as your known location.
After a Range - Angle measurement to the manhole cover in the street is taken, you can take any other offset measurements needed before moving on to your next area. This method requires capturing a backsight point, to calibrate for true azimuth.
Workflow:
a) Occupy your Backsight Point (BS) and log GNSS point
b) Occupy your Control Point (CP) and log GNSS point
c) Aim and shoot at Backsight Point to calibrate azimuth
d) Aim and shoot at target (manhole cover)
3) Range/Range
Range-range offset mapping requires you to take two measurements to log each point. The geometry of a triangle then calculates each coordinate.
This laser mapping offset the most cost-effective. You only need a laser rangefinder in addition to your GPS antenna. When you are collecting geo-location-based information or mapping electric utilities, the range-range method is a perfect choice.
Workflow:
a) Occupy Control Point 1 (CP1) and log a GNSS point
b) Aim and shoot at Target (manhole cover)
c) Occupy Control Point 2 (CP2) and log a GNSS point
d) Aim at same Target (manhole cover)
e) Select 1 of the 2 possible solutions from the displayed map. (For example: if target was on the right of the trajectory from Control Point 1 to Control Point 2, then select the solution on the right of CP1-CP2.)
Real World Applications: Two Case Studies
Analyzing the Game of Golf in Real-Time
Golf has accumulated quite a fan following. The sport reaches the masses through television broadcasts that include all the shot-statistics you could ever hope to know.
These live analytic features require sophisticated technology that operates via a combination of GPS/GNSS receivers, GIS Apps, and laser rangefinders. TruPulse® laser rangefinders utilize the Range-Azimuth mapping method as GPS equipment chimes in to provide control points for the known locations of fairway landing areas.
In the end, this results in a seamless flow of offset measurements that convert into the statistics you expect to see with every drive, putt, and chip shot.
A Zoo of Offsets
Woodland Park Zoo (Seattle, Washington) has 92-acres of impeccable exhibits. It is no surprise that building such large and exquisite displays comes with the expense of needing to make modifications to the zoo's irrigation valves, water lines, underground gas line changes, and more.
A few challenges complicate these tasks further. To start, the assets need to be located and positioned while keeping disturbances to the animal residents at a minimum. Additionally, the zoo’s dense canopy creates a GNSS impaired environment.
Fortunately, a combination of GPS/GNSS receivers, the ArcGIS Collector App, and laser rangefinders make the asset-mapping easy and safe. The Range-Range laser offset mapping method helps eliminate any disruptions to the animals and their daily routines while also offering the ability to map and measure from any location, regardless of GPS connectivity strength.
Laser Tech information
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