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1m Positional Accuracy in Mappt using Bad Elf GNSS Surveyor

Measuring 60x100mm the Bad Elf GNSS Surveyor can provide 1m accuracy

Bad Elf GNSS Surveyor & Mappt Mobile GIS

Measuring 60x100mm the Bad Elf GNSS Surveyor can provide 1m accuracy

Measuring 60x100mm the Bad Elf GNSS Surveyor can provide 1m accuracy

Thanks to the helpful folks at Bad Elf, we recently got our hands on the Bad Elf Surveyor Bluetooth GNSS* for testing with Mappt. Combining Mappt with an external source of positional information delivers higher  accuracy than using the on-board GNSS for mobile phones and tablets. It also reduces battery consumption and CPU load on your mobile device.

Vendors like Bad Elf also provide applications offering enhanced functionality for data logging, device configuration, and data QC. Using external GNSS sources makes determining your position less “black box” and more hands-on when it comes to resolving your location and understanding the level of accuracy provided.
Compact and Compatible
Paring the Bad Elf GNSS with Mappt follows the same procedure we’ve detailed in a previous blog. The compact design (100x 60x20mm) and long lasting battery make the Bad Elf a handy field companion for mobile mapping and data collection. With a small LCD screen yielding important GNSS information, the Bad Elf keeps you well aware of the positional information available to you.

GNSS information available from the Bad Elf's compact 35x25mm LCD screen

GNSS information available from the Bad Elf’s compact 35x25mm LCD screen

Increased Accuracy
When either mapping or collecting data in the field, increased positional accuracy is always a plus. Often it’s necessary to revisit the field to account for seasonal changes (in the case of environmental sciences) or for relocating benchmarks or critical infrastructure such as utilities. The Bad Elf Surveyor offers up to 1m accuracy, an improvement over the 3-5m accuracy achievable with tablets and mobile phones.

 

How does it do that?
The Bad Elf Surveyor uses information from three satellite constellations; GPS, GLONASS, and QZSS. Thus from wherever you are globally, there’s an increased probability that you will have the required four satellites to resolve your position. Many devices derive location from a single satellite constellation thus limiting the amount of satellites available to them. The Bad Elf Surveyor also implements SBAS, Satellite Based Augmentation System, to gain positions within 1m. Serving as an augmentation to Global Navigation Satellite Systems, it works by collecting raw positioning data from regional Continuously Operating Reference Stations (CORS), computing error corrections, and sharing these corrections to users via a geostationary communications satellite. While southern hemisphere regions don’t have their own SBAS, Australia is currently implementing its own SBAS test-bed to be operational by January 2019.
Alongside SBAS, the Bad Elf Surveyor also implements PPP, Precise Point Positioning, which removes GNSS system errors providing a high level of position accuracy from a single receiver. This solution depends on GNSS satellite clock and orbit corrections. These corrections are delivered to the receiver via satellite to provide positioning accurate to within several deicmetres.

 

Mobile Device GPS Behavior Versus Dedicated GPS Units
Mobile device GNSS chipsets have been designed to compliment an integrated system (your tablet/phone) delivering a wide variety of applications. Just count the number of apps you’ve downloaded from the app store. Can you imagine carrying a separate component for each of these?  These mobile applications are optimized to reduce load on the system by reducing battery consumption and processor load. The optimisation for mobile GPS chipsets puts limiting battery usage at the top of the list with time-to-fix location second and positional accuracy third. Dedicated GNSS devices like Bad Elf devices flip this priority on it’s head, placing positional accuracy first followed by time-to-fix and lastly the reduction of battery power. While it may seem like the Bad Elf would quickly run out of juice, it can continuously stream Bluetooth GNSS information for 24 hours. We have yet to see a tablet with that type of battery power!

We took the Bad Elf GNSS Surveyor to our favourite bushland, Signal Hill Park

We took the Bad Elf GNSS Surveyor to our favourite bushland, Signal Hill Park

Mapping Tips n Tricks Learned Using the Bad Elf Surveyor
Creating Polygons in Mappt –  Turn on the enter polygon tool and record each significant point of the polygon (corners and inflection points) as you walk out the perimiter. This ensures that corners/vertices are not shortcut and an accurate shape of the area is recorded.  It’s possible to create polygons in Mappt using the GPS Tracking tool, then walking out the perimeter of the polygon, and finishing off by converting the polyline to a polygon to enclose the area. This method helps when moving continuously (such as when in a vehicle) as you don’t need to stop and record points around the area. However the points associated with your polyline are created at the frequency of GPS updates from your device and you may end up not recording those key corner points!
GNSS Location – Place your external GNSS device in a way that provides a clear view of the sky. Some websites suggest affixing the GNSS face-up to the top of your hat! While you will have great reception, this limits the opportunity to check parameters on the LCD screen. Affixing the GNSS to a surveyors staff gives you both a walking stick and place to mount your tablet. This setup affords both good GNSS reception and makes data entry easier as the tablet is held steady by the staff.  Note:  The team at Bad Elf are currently developing hardware designed with rapid mobile mapping in mind.

The crew at Bad Elf are working on a clever monopole mount for the Bad Elf Surveyor

The crew at Bad Elf are working on a clever monopole mount for the Bad Elf Surveyor

Bad Elf has developed an integrated GPS and mobile device monopole for rapid mobile mapping

Bad Elf has developed an integrated GPS and mobile device monopole for rapid mobile mapping

Bad Elf GNSS Logging – The Bad Elf allows continuous logging of points. After a hard day in the field, it’s nice to know how much ground you covered. Logged information can be downloaded as GPX files and visualised in desktop GIS solutions such as QGIS.

Signal Hill Park Map from QGIS. Bad Elf track points (orange) displaying the total ground covered in this mapping exercise.

Signal Hill Park Map from QGIS. Bad Elf track points (orange) displaying the total ground covered in this mapping exercise.

*GNSS, Global Navigation Satellite System, is the collective term for all navigation satellites groups (constellations) including GPS.

 

If you would like to know more about configuring an external GNSS to work with Mappt, please contacts us at: support@mappt.com.au