Request for information – FOI13405
Thank you for your e-mail, of 8 August 2013, which we acknowledge and have assigned the new reference of FOI13405.
Ordnance Survey does hold some the information to respond to this information request, which relates to information we have previously supplied under FOI13394, and we respond to each of your points as follows:
1. Attached is a modified version of your screen shot of the area (omitted from this response). I have assumed that the red points on the 4 to B lines and elsewhere are points where direct GPS readings were taken. If so, I have marked in purple, 10a and 10b whose readings would also be needed.
Yes, this is correct. Points 1 to 6 on the original 'coords.bmp' are 'direct GPS readings'.
10a X and Y coordinates 17741.97 703358.54 and Z value 183.09
10b X and Y coordinates 317743.49 703357.22 and Z value 183.14
2. I note the D to A/G line (extended to A/G) has no direct reading points although the deeds specify dimensions related to A/G. Is this correct? If not, may I please have the readings that were taken on this line, or the coordinates as read from your drawing.
The line to which you refer as D to A/G has one 'direct GPS reading' (control point) approximately 2.4 metres from the north end of the line. The X and Y coordinates of this control point are 317819.98 703369.01 and Z value 197.31.
The other points labeled by you on this line have no direct GPS readings. The coordinates taken on screen are:
Point G/F 317785, 703349
Point F 317779, 703346
The coordinates taken on screen for the Southern end of line D to A/G (not the extended part drawn on by you) are 317768, 703340.
Please note that whilst control point features are frequently coincidental with topographic detail that meets our specification, control point features (point 10a for example) may, exist in isolation, and may be purely reference points.
3. The accuracy tolerance quoted seems exorbitant. Is this the figure that is required by the Registers of Scotland that is specified by the manufacturers of the GPS system?
We have previously supplied our general accuracy in relation to the expected accuracy of the data for this type of geography i.e. developed rural areas or smaller urban areas. In some areas the accuracy will be better and individual surveys may well be better than the quoted figure.
Under the duty to provide advice and assistance, section 16 of the FOIA, we can advise that although we use modern high-accuracy equipment to support our data capture, we are revising mapping that was produced using less reliable techniques. We have to make compromises when fitting new surveys to the existing mapping; hence the generous tolerances for relative accuracies.
We can advise that The Registers of Scotland are aware of the expected accuracy levels for Ordnance Survey large scale mapping. We cannot comment on the accuracy of independent GPS systems manufacturers.
As all the requested information that is held has been provided, we have determined that in all the circumstances of this case the Public interest consideration (section 17 FOIA) is not applicable in this instance.
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