Historical Surveying / Geeky Theorising
You all must know how I love geeky stuff, so when evilmattikinz sent me a note about a couple of old OS photos with an enquiry about what they meant.... and I couldn't resist, and replied...
The photos are obviously OS photos as part of the records for the marks concerned. As for whether they are horizontal controls (triangulation stations) or vertical controls (benchmarks) I'd go for the latter
despite of the "STN" (station; implying horizontal) labelling at the top of one of the pictures. The dating corresponds with the Third Geodetic Levelling - evidence from OS annual report (http://www.deformedweb.co.uk/trigs/annual.cgi) suggests that Lancaster tertiary levelling (exactly this sort of thing) was completed prior to April 1954 - so I think these may be the third-order benchmarks being recorded. For further argument in favour of this, see below:
Obviously the date is at the top of the board - the next numbers (09A or 71B ) I think are just the designation of the mark in the current grid square - which is the next line: SD4861 (in Lancaster) a square which interestingly also contains a fundamental bench mark. Denis Street is identifiable in google maps and is indeed in that square. The other is possibly a shot of Williamson Park (where the FBM is and which has many benchmarks in it). There's a fair bit of parkland in the area and it's a bit anonymous.
I had a theory that if they were benchmarks then the last line was a serial number of the mark in the levelling - levelling line 55 was Hoghton to Lancaster. An individual levelling line and attendant
campaign might be significant effort, so the 55/ would be painted on the board because everything along that line would need it (not 100% convinced on this!)
Note that the marks on the photos suggest they have been destroyed - unsurprising really as benchmarks are lost all the time and there is little reason to replace them.
Enough!
Benchmark spotting geekery HQ
Digitising the data from the 1922 report
Yes, they were doing surreal photos in 1922, too
The photos are obviously OS photos as part of the records for the marks concerned. As for whether they are horizontal controls (triangulation stations) or vertical controls (benchmarks) I'd go for the latter
despite of the "STN" (station; implying horizontal) labelling at the top of one of the pictures. The dating corresponds with the Third Geodetic Levelling - evidence from OS annual report (http://www.deformedweb.co.uk/trigs/annual.cgi) suggests that Lancaster tertiary levelling (exactly this sort of thing) was completed prior to April 1954 - so I think these may be the third-order benchmarks being recorded. For further argument in favour of this, see below:
Obviously the date is at the top of the board - the next numbers (09A or 71B ) I think are just the designation of the mark in the current grid square - which is the next line: SD4861 (in Lancaster) a square which interestingly also contains a fundamental bench mark. Denis Street is identifiable in google maps and is indeed in that square. The other is possibly a shot of Williamson Park (where the FBM is and which has many benchmarks in it). There's a fair bit of parkland in the area and it's a bit anonymous.
I had a theory that if they were benchmarks then the last line was a serial number of the mark in the levelling - levelling line 55 was Hoghton to Lancaster. An individual levelling line and attendant
campaign might be significant effort, so the 55/ would be painted on the board because everything along that line would need it (not 100% convinced on this!)
Note that the marks on the photos suggest they have been destroyed - unsurprising really as benchmarks are lost all the time and there is little reason to replace them.
Enough!
Benchmark spotting geekery HQ
Digitising the data from the 1922 report
Yes, they were doing surreal photos in 1922, too
