Testing MapRun “GPS Punching” in a Forest

Updated 2 May 16:00

At the Downhill Score Training on the 1st May we took the opportunity to test the latest version of MapRun (V6.0) in a forest environment.

The existing Downhill map was based on professional photogrammetry and it was therefore easy to a do basic georeference – see below:

The basic match is good, but on close inspection some edge areas don’t match up

The southern tip boundary with the housing and the south-western field boundary suggest possible drift from ground survey.

There were also significant issues with the finish contro:l

While the georeferencing for the start is good, the main road is significantly closer than show on the map (see shadow of map overlay). To be in the centre of the circle you would actually have to have crossed the road!

The courses were planned by Des using Purple Pen, but with the un-georeferenced map. This meant that I had to duplicate the controls (again in Purple Pen) onto the Georeferenced map. Small errors in this process partly account for some of the missed punches. 106 to the east of the map below was definitely misplaced by me and almost certainly account for some runners “missing the beep”.

There is a major discrepancy at 104 in both courses, suggesting an issue with the map boundary.

The line match to terrain, even adjacent to steep slopes and mature forest remain good on 3 phones with no apparent random jumps or obvious ghosting from reflections. However on the other 2 phones jumps did occur in several places.

Although the number of runners was small, the results I think are good enough to justify more experimenting in this area. Owing to Covid and travel restrictions we kept the event simple and did not control the GPS accuracy of the chosen points.

For future events I would suggest:

  1. Only try this with a map based on a single high-quality base map or PG plot
  2. Georeference the map first and give to the planner (no transcribing)
  3. Ground survey each site with a MapRun to spot problem map areas

It is likely that the club will be able to obtain a LIDAR base for the whole of the Downhill / Castlerock Area. This should allow for a quick remap with almost all features correct in absolute rather than relative position. Such a map should take MapRun GPS events to a whole new level of accuracy.

Charlie Reid

May 2020