Monthly Archives: September 2016

Developments

The page below has mysteriously disappeared from the website pages and is now reinstated as a page and as a post.

After sifting through the numerous pages of calculations and speculations accumulated over years of intermittent research it became apparent that a decision must be made to settle on some criterion upon which all this data could be based.  There were two lines which stood out from the others as extraordinary – the Newlands line with its precise alignment and distances, and the Crooksbury line with its newly discovered barrow and precise alignment.  The bearing of the Newlands line was 132.82 degrees and the Crooksbury line 232.32 degrees.  It has already been seen that the rays are around ten degrees apart and by dividing the difference by ten for the intervening rays we have an interval between each ray of 9.95 degrees.  This interval was applied to all rays in the pattern and a list was compiled of the intersections of these revised rays and the distance points at one Druid Mile (DM) intervals from the base point of the rays at Whitmoor Barrow.  These points were then compared with the physical detail as shown on the Ordnance Survey as downloaded to the computer database.  This was straight forward for circular structures such as barrows where the centre point was fairly obvious but when passing through a building a best estimate of the centre was used.

By 2012 the technology of hand held GPS instruments was very advanced with an accuracy good enough to make them a suitable tool for field research, so the decision was made to surf the internet for an instrument with the most suitable specification.  I settled on the Garmin GPSMAP 62 and carried out some field tests to check the accuracy.  Results varied from nearly perfect to, in the worst case, eight metres of error when compared with known Ordnance Survey (OS) co-ordinates established by professional surveying instruments.  Because of these variations it was necessary to revisit critical sites to re-record the co-ordinates and take an average of several readings.

Once a few sites had been visited with the GPS and the results plotted onto the database it became clear that there was a discrepancy between the WASG grid used by the Garmin instrument and the OS  grid titled OSGB36. There is a lot of information on the OS website about how this grid originates and how to use conversion programs to compute very precise coordinates. Although the grid used by Garmin is called OS grid in the format selection, it did not appear to conform to the OS map grid. Therefore it was decided that to check the difference between the two grids.  Check readings would be taken on-site from known points. First chosen was the OS trig pillar at Jacobswell just south of Whitmoor Barrow. Trigonometrical pillars are usually concrete structures, standing around four to five feet high, and constructed on prominent hill tops affording views over long distances and are part of the network of triangulation stations upon which the OS of Britain is based.  Also points were taken on the corners of other sites such as the church and churchyard walls on St Martha’s Hill. When these were plotted into the database it was seen that there was indeed a discrepancy. Due to the inherent inaccuracies of Ordnance Survey detail it is not possible to attain spot-on fitting of data. After meaning out the various results and taking the trig pillar coordinates as being the main data point it was seen that all GPS data needed to be moved 8 metres south and one and a half metres West. It would have been possible to calculate a very precise difference between the two groups but the accuracy of the hand held GPS is no better than about 7 feet or two metres, therefore it would seem that refining the difference between the two groups would be excessive and a waste of time. I have since confirmed these conversion factors by taking readings at other pillars in West Surrey.

The first exercise with the new instrument was a visit to Whitmoor Barrow.  I walked around the ditch taking readings at about five metre intervals.  Each reading was taken after holding the GPS at eye level pointing in several directions until the readout settled down and became constant.  These readings were stored as waypoints in the instrument and transposed onto my AutoCAD base plan in the office.  The Ordnance Survey extract of the barrow were already on this plan and it was seen that the adjusted GPS co-ordinates and the map co-ordinates of the barrow were an excellent match.  This confirmed my intention of using the Whitmoor Barrow as the base point for the overall pattern of rays.  A similar exercise was then undertaken at Culverswell Barrow and at the twin Crooksbury Barrows a short distance away.  The co-ordinates of the Culverswell Barrow confirmed my original theodolite survey of some years ago and the co-ordinates of the Crooksbury Barrows again proved an excellent fit.

Buoyed up by these satisfying results I was keen to use these new-found techniques to discover other lost sites.  The first I looked at was the Mount Pleasant Barrow on Whitmoor Common.  This is marked on The OS as the site of an Ancient Monument no longer existing.  The co-ordinates on the OS were noted as was the co-ordinates of the point on Mount Pleasant line being at a bearing of 252.22 degrees and one Druid Mile from the base point (Whitmoor Barrow).  The common is a flat area of land surrounded by woodland to the north, a railway to the east with roads on the other two sides.  On reaching the supposed site of the Ancient Monument nothing could be made out amidst the rough tussocky grass but on navigating to the point on the pattern some seventeen metres to the north west a circular bank some seven metres in diameter could just be made out beneath the scrubby birch trees (see photos at header MOUNT PLEASANT LINE).