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MikeO
28-05-2012, 15:07
I have a full listing of the ww2 airfield decoy sites. I don't think this ever has been included in AR but stand ready to be corrected. As for the locations, there are 1940s Military Grid references. I wonder if anyone knows how to convert those into modern day NGRs?

AiXAdmin
28-05-2012, 15:58
If nobody pitches up with a suitable converter I may be able to help... I wrote a little software app to do these types of map conversions. I may be able to incorporate such a conversion for batch processing.
Please let me have a few sample entries... PM for an email address.

Cheers
Dave

David Thompson
28-05-2012, 16:48
I'm pretty sure we have had this question on the forum before and Carnaby may have the answer ?

tigger
28-05-2012, 16:50
Steve's extended DoB google earth overlay already has those listed by Dobinson.
Easy enough to extract those with co-ordinates

a10694
28-05-2012, 18:11
I've always found the DoB references, and Dobinsons, to be plus/minus a field or two. I've always debated as to what they are the reference of - bunker, centre of decoy site, SW corner of.....

I know from my own experiences that certainly some of the sites do not show at all on NMR aerial photos, so any location cannot be truly accurate for those.

Peter Kirk
28-05-2012, 18:15
I always use this site http://www.fieldenmaps.info/cconv/cconv_gb.html

As long as you have the wartime two letter prefix. Accuracy depends on the number of numbers. Normally the result in the rough area but not the exact location.

MikeO
28-05-2012, 23:02
Much appreciate responses to my question. I will set out a few examples of what I have and perhaps we can see whether a translation to current NGRs is possible.

Site No 12b was Kilham, a decoy fror Driffield and the listed grid reference is 28/557828.

Site No 26 was N. Tuddenham, a decoy for Swanton Morley grid reference 66/493317.

Site No 121 was Marsh Chapel, the decoy for Donna Nook, grid reference 40/871192.

All these from an August 1942 listing

MikeO
28-05-2012, 23:12
Should perhaps add that the references are as per the one inch OS maps and I imagine the first two numbers indicate the sheet number in that series.

tigger
28-05-2012, 23:47
I've always found the DoB references, and Dobinsons, to be plus/minus a field or two. I've always debated as to what they are the reference of - bunker, centre of decoy site, SW corner of.....

I know from my own experiences that certainly some of the sites do not show at all on NMR aerial photos, so any location cannot be truly accurate for those.

I suspect the figures quoted being a field or two out is probably accurate enough given the scarcity of remains. Some quoted figures seem to be a nominal centre, some seem to be the bunker and some don't seem to relate to anything (in the sense that nothing can be found near them). The control bunkers were sometimes quite distant from the actual fields used (eg. Betchton).
Will be interesting to see if the references MikeO has are actually any better than the ones Dobinson uses (which must have come from a similar source)...but how will we actually know!

On the subject of conversions, I have found 'fieldenmaps.info' to have some large errors on some conversions.

Peter Kirk
29-05-2012, 08:47
Most converters seem to have errors but I think they tend to be in certain areas where the "rules" do not work correctly.

There was a one inch map sheet guide on the internet at one time and I used to overlay it over the wartime grid uk map to get the two letter prefix. A bit hit and miss where they overlap but you can usually deduce where the correct location was.

tigger
29-05-2012, 10:12
to pass a few minutes whilst my tea was stewing I converted the examples posted earlier and plotted them on current 1K25 mapping. Very close (same field!) to the positions given by Dobinson.

Going back to earlier comments about accuracy: The six figure reference describes the bottom left corner of a 100m square. It is a precise and accurate reference to that corner point (as long as we know the projection and datum). Converting co-ordinates between different systems is not trivial. My calculations (and those performed by online conversion sites) are only accurate at a specific mathematical point. For our purposes as airfield archaeologists trying to locate a large object the errors are not significant but people need to be aware of them.

For War Office maps using the Cassini grid the following photo (I don't have a scanner) from "Manual of Map Reading, Photo Reading, and Field Sketching", The War Office, 1929, might help people.

http://i130.photobucket.com/albums/p267/trunktemp/mapping/britishgrid.jpg

The book is well worth having if you need to interpret old British military maps

Peter Kirk
29-05-2012, 12:26
Unless I am mistaken the Irish grid is the same as wartime, just need to substitute the correct letter, which is fairly easy to do even by trial and error. It has worked so far.

MikeO
29-05-2012, 16:44
Thanks for all the responses. After consulting the Charles Close Society website, I reckon the references that I have in AIR 20/4352 come from One-inch Popular Edition map of England and Wales
with War Office Cassini Grid, GSGS 3907 and that the digits before the / are definitely sheet numbers.
Leaves the problem that the converter is looking for a two alpha prefix whereas I have up to three numeric.
I have clicked to the notion that 'Dobinson' refers to the book "Fields of Deception". I must have missed that when published. Fortunately I find I can get it on an inter-library loan. Just as well, because Amazon's best offer is north of 43.

tigger
29-05-2012, 17:18
MikeO, if you use the map i posted above with the charles close index to popular series you can get the two letter prefix for use on fieldenmaps
If you want the data from Dobinson i can post it

MikeO
29-05-2012, 18:00
Many thanks Tigger. I will have a play later on. Meanwhile, appreciate the very kind offer but book is already on order and orders usually get through in a very few days.

The origin of my query is that on reading Richard's plea for AR articles, I went through various papers I had copied from the National Archives and elsewhere over the years and hit upon the decoy listing as a possibility. Certainly would need modern day NGRs, even supposing the subject appeals and hasn't been done in AR before.

tigger
30-05-2012, 11:45
......even supposing the subject appeals and hasn't been done in AR before.

It appeals to me and I'm sure would make a very good article for AR that would interest most of our membership.