observations. The data would then be post-processed to give Guernsey Grid co-ordinates and height above Guernsey Datum. This would be in preference to using less precise Real-Time-Kinematic (RTK) observations. Further site control would be established as necessary by closed loop traverse. A minimum of two Permanent Ground Markers (PGMs) would be established with PK or Hilti nails in hard material or Perma Marks in soft material.
The maximum error between survey control stations would not exceed 1 part in 20,000 for distances exceeding 200m. For shorter distances the maximum error would not exceed ±10mm.
Height control would be established by closed double-run levelling using either a convenient OS bench mark, Precise Levelling Point or the value of one of the survey stations observed with static GPS.
The height difference between any two survey stations would not be in error by greater than:
±12 x √k mm
where k is the distance in kilometres between the points being considered, or ±5mm, whichever is the greater.
All survey observations would be made with either a Leica Geosystems TCRA1102 plus or a TCRP1205+ Total Station.
Detail recorded would include:
building outlines at ground level with ridge and eaves levels noted
boundary features with type and levels of top noted
trees with trunk diameter and spread shown to scale and with height and
spot heights at nominal 5m grid as required and at any significant changes
in level contours at 0.5m vertical interval
service covers shown to scale with cover level, invert level and type noted
overhead detail including service cables
other hard detail; i.e. walls, steps, channels, changes in surface material etc.
line and level of roads
Detail would be recorded such that the plan position of any well-defined point of detail should be correct to within 0.3mm rmse at the plan scale when checked from the nearest survey station.
Nominal survey scale of information provided would be 1:100.
Downloading and Processing
Data would be downloaded into LSS survey software via Leica Geosystems’ Geo Office. A large proportion of data editing would be carried out using LSS before exporting the data to AutoCAD for final editing and production of finished drawings.
Co-ordinates would be in metres in Guernsey Grid, while levels would be in metres above Guernsey Datum. The survey drawing would be merged with digital mapping to provide context, and the map data would be annotated with house names and ridge and eaves heights of buildings neighbouring the site.
Drawings would be delivered by email or on CD in pdf or AutoCAD R14 format with A1 layout tabs for plotting at 1:200.
Paper or film copies would be produced on request.