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Ground-truthing Saltmarsh Vegetation Communities with Mappt. Lindisfarne Island, UK

lindisfarne_collage

Lindisfarne is a tidal island located off the north-east coast of England covering 405 hectares (1,000 acres). Whilst small, measuring 4 km in width 2.5 km in length, the island habitats consist of thriving saltmarshes, sand dunes, and tidal mudflats.  The island is known as a spectacular habitat for viewing migrating birds.

The coastal salt marshes of Lindisfarne formed when salt tolerant plants colonised the adjoining intertidal areas. The region’s high tidal variation has created an environment endemic to the islands unique range of flora and fauna.

How Mappt Assists Uni Students in the Field

Post-graduate research students enrolled in an International Marine Environmental Consultancy course provided by Newcastle University, UK, successfully used UAV imagery and Mappt to identify saltmarsh vegetation communities around Lindisfarne Island.

Students used stratified random sampling to collect ground truth data in order to train predictive mapping models for object-based image analysis of drone imagery. Students identified eight vegetation communities for predictive mapping.  Method “C” was found to have the most successful prediction rate.

Tidal plant communities on Lindisfarne island mapped using image-based object analysis of drone imagery

Tidal plant communities on Lindisfarne island mapped using image-based object analysis of drone imagery

Vegetation Communities Identified for this study

Code & Salt Marsh Plant Community Name

SM13 Puccinellia maritima
SM14 Halimione portulacoides
SM15 Juncus maritimus-Triglochin maritima
SM16 Festuca rubra
SM28 Elymus repens
SM6 Spartina anglica
SM8 Annual Salicornia

 

For this study, Mappt was connected to a Trimble Catalsyt GNSS (via bluetooth) to stake out quadrats, navigate to sampling areas, and store field data.  *Mounting your tablet to the GPS pole as was done for this study is advantageous as it frees up your hands for other important tasks.  We like how Paula took advantage of soft soils to ‘plant’ her GPS and tablet while referring to her comprehensive list of 864 unique National Vegetation Classification sub community names.

Using Mappt in conjunction with Trimble GNSS to map tidal plant communities

Using Mappt in conjunction with Trimble GNSS to map tidal plant communities

Student feedback was overwhelmingly positive and included the following;  

Uploading shapefiles was easy

Sampling points when overlain on drone imagery were easy to navigate to  

Sampling points could be made invisible after data had been collected

Students Share Their Excitement for Using Mappt

Students Share Their Excitement for Using Mappt

Students at the university of Newcastle plan to use Mappt for their future projects such as; sand dune monitoring, rocky shore habitat mapping, and measuring the impact of activities such as bait collection from the intertidal area. In this way, Mappt is helping university students to map and collect data on-the-go effectively.

 

Mappt is available for free to educational institutions.  Here’s how to become an educational partner with Mappt.  

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1m Positional Accuracy in Mappt using Bad Elf GNSS Surveyor

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

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External GPS sources for Mappt Part 2: Mapping in the Field with RTK GNSS (survey-grade GPS)

In our last post we covered how to configure your tablet or phone to receive an external GPS signal via Bluetooth.  Here we share our experience of linking up Mappt with survey-grade RTK GNSS (Real Time Kinematic Global Navigation Satellite System) to achieve centimetre-level positional accuracy.

 

Utilising RTK GNSS and Mappt for centimetre-level positional accuracy

Utilising RTK GNSS and Mappt for centimetre-level positional accuracy

Achieving Survey-Grade Positional Accuracy with Mappt

Joe user asks, “Hey how can I achieve high positional accuracy with Mappt?

The short answer is, “Bluetooth to an RTK GNSS to achieve centimetre level accuracy“.

What’s GNSS?

GNSS, is the collective term for all satellite positioning systems which includes GPS (USA), BeiDou (China), GLONASS (Russia), Galileo (Europe), IRNSS (India), and QZSS (Japan).  Phones, tablets, and survey-grade systems use satellites from multiple positioning systems, thus we’re referring to these systems as GNSS (rather than GPS).

The Benefits of Using Mappt in conjunction with RTK GNSS

Mappt’s flexibility and onboard functionality helps users achieve the full benefits of high accuracy RTK GNSS while in the field.  For example when using Mappt in conjunction with RTK GNSS, users have in-field access to these mapping tools;

  • Locate and save point features with unlimited attributes
  • Thematic Mapping gives users the ability to colour code mapped information while in the field
  • Layering of data types to achieve hierarchal data structure and visualisation
  • Interactive functionality (exclusion & inclusion zone warnings) improving field safety
  • The ability to display web-based aerial/satellite imagery and other GIS information such as WMS, WMTS, & WFS
    • With a data connection, this data is continuously updated as you move to new areas
  • Offline display of high resolution aerial and satellite images (ECW, JP2)
  • Multi-user data capture & updates using MapptAir.

RTK GNSS Gear

In our previous post we detailed how to configure your mobile device to receive location information via Bluetooth.  Thanks to Mangoesmapping and Ascon Surveys both for their technical support and equipment (on loan) used to complete our trial.  We found the Emlid Reach RS RTK GNSS units (available from Mangoesmapping) suitable for this trial.

Our Field Experience

The following data was acquired in less than one hour (including setup and pack down of the RTK base unit and survey pole mounted rover unit).  Data collection in this small urban bushland was on-the-fly as point types were added as deemed necessary.  Points types collected included kerb locations, footpath limits and walking tracks.  Point types were added to our field form as necessary thus the list of point types was added to as new elements were observed.  *To save time, a dropdown list of point ID’s can be created prior to leaving for the site.  In the limited time spent onsite, three point IDs were all that was necessary.  We also utilised the geotracking utility to map in the trails crossing the site as well as to create a geofenced area at the park’s centre.  Lastly we tested Mappt’s geofence alerts feature by entering and exiting our geofenced area.  Have a look at this video showing how it works.

Mappt mobile GIS data gathering using RTK GNSS at Signal Hill, Belmont, WA

Mappt mobile GIS data gathering using RTK GNSS at Signal Hill, Belmont, WA

What we took away from the experience.

It was a simple step to download all data gathered to shape files and import them into QGIS.  We mapped in such features as the back of kerb, footpath limits, and bush tracks.  RTK GNSS units have the ability to validate/qualify positional information with an audible “Fixed” to indicate that positional information is within your specified accuracy.  Likewise when the positional information is below spec an audio warning “Float” will alert users that possibly more time at that location is needed to gain a fixed position or that trees or buildings are hampering satellite reception.  Our recommendation is to have this activated on your RTK GNSS receivers to eliminate collecting data of low positional uncertainty (occurs in areas of high tree cover and when adjacent to tall buildings) .

QGIS map showing GIS data gathered using RTK GNSS and Mappt

QGIS map showing GIS data gathered using RTK GNSS and Mappt