Saturday, 1 November 2014

Trimble Survey Spreadsheet – Introduction

Each survey conducted with the Trimble GeoXH 6000 will have a posting written about it on the Mapping Mountains blog.  A link via hill name is given in the ‘Labels’ on the right hand side of the blog for those wishing quick access to specific hill surveys.  Each posting will also have the survey result included at the end of the post.  Individual survey posts will be linked to the Trimble Survey Spreadsheet; this is where greater detail can be found.  The data in the spreadsheet is arranged with all survey points relating to the same hill being grouped together, even if the surveys took place on different days.  The summit data precedes that of the bwlch, even if the latter was surveyed before the former.  Each height given in the spreadsheet is in metric.

To see the Trimble Survey Spreadsheet click {here}

The spreadsheet consists of the following:

Number (P14):  The increment number of P14 summits surveyed.

Number (P20):  The increment number of P20 summits surveyed.

Number (P30):  The increment number of P30 summits surveyed.

Date:  This is the date of the survey.

Time:  The time during which the survey took place.

Satellites:  The number of satellites the equipment is fixed onto during the survey.  Only one note of the number of satellites is ever documented, but this number can fluctuate as different satellites drop out of view and others come into view.

Points:  The Trimble is set on a one second epoch time; these data sets are known as points.  As a minimum of two minutes is recommended for data collection, the number of points that appear is this column should never be below 120.  During the Mapping Mountains Trimble surveys the minimum number of points collected are usually 300 (5 minutes).

Group:  This is the group / range that the hill is part of.  For example; Carnedd Llywelyn (SH 683 643) is part of the hill range known as the Carneddau.

Cardinal Hill:  This is the ‘parent’ hill to the hill that has been surveyed.  These ‘Cardinal Hills’ are the highest or most prominent hill in the respective area.

Region:  Three Regions are used for Wales; North, Mid and West, and the South.  Each Region is an area of land that has been split topographically and geographically following the lay of land using contours, streams, rivers and bylchau. 

Sub Region:  The three Regions of Wales comprising the North, Mid and West, and the South are divided into Sub Regions with the North taking in four Sub Regions, Mid and West comprising a further four Sub Regions, and the South being divided by a further three Sub Regions.  All are split by the use of contours, streams, rivers and bylchau. 

Hill Number:  This is the unique hill number used in the Database of British and Irish Hills (DoBIH).  Occasionally a hill will be surveyed that has no current number in the DoBIH, the reason for this is that at the time of the survey the hill is not listed in this database.

Name:  This is considered the most appropriate name of the hill.  Sometimes the name used does not correspond to current Ordnance Survey map spelling or the name may not appear on any map.  Where no appropriate name has been discovered for the hill from any source, the Pt. (for example; Point 444m) notation is used rather than making up a name that has no local or historical evidence of use.

Alternate Ordnance Survey Name:  If the name composition as chosen by the Ordnance Survey is different to the one considered the most appropriate it will appear in this column.  For those names that do not have alternate Ordnance Survey composition N/A (Not Applicable) will appear in this column.

1:50,000 Map:    This column gives the number of the 1:50,000 Ordnance Survey Landranger map that the point surveyed appears on.

1:25,000 Map:    This column gives the number of the 1:25,000 Ordnance Survey Explorer map that the point surveyed appears on.

Grid Reference (Map):  This is the ten figure grid reference taken to a map spot height or a centralised position for an uppermost contour that has no spot height.  

Summit / Bwlch:  As all surveys are envisaged to be either to a summit or bwlch position, this column details which is being surveyed.  When surveying hills in England the word ‘Col’ will appear instead of the word ‘Bwlch’.

Map Height (m):  This gives the map height in metres of the hill above Ordnance Datum Newlyn (ODN), often referred to as sea level.  Where a ‘c’ (contour) appears preceding the height it means there is no known spot height available.

Processed Survey Height (m):  These are the heights attained from each survey after post-processing.  Each height is given to three decimal places; this is then rounded up or down to one decimal place when the height is quoted in the survey post on the Mapping Mountains blog.  When drop values are quoted in the blog post they are attained from subtracting bwlch height from summit height using three decimal places and then rounding up or down the result to one decimal place.  Because of this the quoted drop figure does not always compliment the subtracted bwlch and summit heights that are quoted to only one decimal place.    

Processed Survey Height (m) OSGM15:  These heights correspond to the new geoid model (OSGM15) released by the Ordnance Survey in 2016. 

Grid Reference (Survey):  This is the ten figure grid reference from where the survey was taken.

Drop (m):  This column details the relative height of the hill; this is commonly referred to as ‘drop’, ‘prominence’ or ‘reascent’.  The drop is the height difference between the summit and bwlch connecting the hill to next higher ground along the watershed.  The letter ‘c’ before the drop figure signifies there is no spot height known for either summit or more usually, the bwlch, therefore a part of the drop figure has been estimated from contour interpolation.

Dominance (%):  This column details the Dominance of the hill, which is given as a percentage.  The qualification for the Dominant list are those P30 hills whose prominence equal or exceed half that of their absolute height, with a sub category listing those additional P30 hills whose prominence is at or over one third but below half that of their absolute height.  All hills have Dominance and therefore their percentage figures are given, even though some hills may not qualify for the Dominant list.  

Status:  This gives the class of hill be it a Marilyn, Hump, Simm, Uchaf, Pedwar or Twmpau at the time the survey result was obtained. 

Measurement Uncertainty (m) (Height):  Unless the summit of a hill is obvious there will always be a level of uncertainty in chosen position when operating without a level and staff.  This column details the estimated height uncertainty in metres for each survey. 

Standard Deviation:  This column gives the standard deviation (variation or dispersion from the average) quoted during processing.  A relatively low figure indicates data points that tend to be close to the mean, whilst conversely a relatively large figure indicates data points that are spread over a large range of values. 

Position of Trimble:  This column gives the position of the Trimble for each survey.  As the majority of surveys will be conducted with the Trimble GeoXH 6000 with its internal antenna aligned to the survey point, this column will have ‘Trimble on ground’ repeated many times.  However, occasionally surveys will be conducted where the equipment will be positioned either on a pole and / or tripod.

Measurement Offset (m):  The figure quoted in this column refers to the height between the antenna and the point to be surveyed.  This measurement can be calibrated in to the equipment prior to survey or it can be taken in to account after post-processing.

Estimated Accuracies:  This is the quoted figure during post-processing.  Every data set collected will have a range of accuracy compared to the position of survey or length of survey.  The range of this accuracy is given in centimetres, only the highest percentage of range spread is quoted in this column.

Terrain:  It is considered good practice to document each survey position by a note of the terrain, for example; if the survey equipment is placed on a rock, or grass, or in a heathery bog.  Each survey position is also documented by photograph (when remembered!), these can surprisingly be vital when reviewing post survey, a video is even better.

Base Stations:  This column is used to document what base stations are used during post-processing.

Further Comments:  Any further comments that are not covered in the previous columns will appear here.

To see the Trimble Survey Spreadsheet    click {here}

Thanks to Alan Dawson, John Barnard, Graham Jackson, Mark Trengove, Aled Williams and Jeff Parr for advice with the layout and content of the spreadsheet.

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