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pgrig

Need Help Converting Army WW2 Coords to Lat/Long

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Hi Folks--

 

Patty's post on the new Google Maps features reminded me of my ongoing problem.

 

I am doing a lot of work (brought on by an excess of benchmark hunting) finding and describing the features of the Boston Harbor Defenses from WW2. The Army (the Coast Artillery, actually) had a local coordinate system for describing these features. Below is a schematic map of the coordinate system, from 1943.

 

I would like to be able to find the lat/long of items for which I have coordinates (e.g., individual guns). I could easily pull together a number of pairs of Army coordinates vs. lat/long for certain points (benchmarks, in fact--like fire control tower positions). Can anyone tell me how to come up with a (hopefully simple :-) system for doing the conversion for any set of Army coordinates?

 

Thanks,

-Paul

 

local_coordinates_1943.jpg

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I am doing a lot of work (brought on by an excess of benchmark hunting) finding and describing the features of the Boston Harbor Defenses from WW2. The Army (the Coast Artillery, actually) had a local coordinate system for describing these features. Below is a schematic map of the coordinate system, from 1943.

 

I would like to be able to find the lat/long of items for which I have coordinates (e.g., individual guns). I could easily pull together a number of pairs of Army coordinates vs. lat/long for certain points (benchmarks, in fact--like fire control tower positions). Can anyone tell me how to come up with a (hopefully simple :-) system for doing the conversion for any set of Army coordinates?

 

Thanks,

-Paul

 

A long time ago there was a thread on the WWII military grid that preceded UTM. The thread starts off with a lot of guesswork, but by the end, some research had uncovered a lot of useful information.

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Thanks, Holograph--

 

An interesting thread you posted! I read through it very quickly, but am still not sure if it solves my problem.

 

I found this site through a Google search and have emailed them for an answer. Maybe they'll let me use their s/w for less than $160. ;) From their page, it looks like my coordinates might be MA State Plane. I'll wait and see if someone very smart enlightens me... :)

 

-Paul

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Paul, are any of those places for which you have both sets of coordinates visible on the map? Judging by the scale, I'm not sure they are. But if you could locate a few, you could calibrate the map to those. Then you could click on any other place on the map and get its lat/long.

 

Patty

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Search for CORPSCON, a free software package from the US Army Corps of Engineers that is linked from somewhere on the NGS site. It will convert Lat-Lon to State Plane Coordinates in feet or meters. You will have to deal with the conversion to yards yourself.

 

There is probably a simple offset between MA SPC and your grid that will get you close. If it doesn't fit well enough the extremes of your area, you might also have to do a scale factor of 0.999xx or 1.00xx as well as the offset. Given the limited area, you probably do not need such accuracy to worry about where their standard meridian is.

Edited by Bill93

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I doubt it would be Mass State Plane. Note the scale on the map.....the coordinates are in Yards. In addition to the local coordinate grid, the map also shows Lat/Long grid ticks....probably in NAD27 considering the time period. The "true north" arrow implies that the grid is aligned with geodetic north, although depending on the projection this could only be true along one meridian.

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If you are only looking for the coordinates you might try this URL

 

At the bottom of the post is a URL to download a KML file that has the location of forts and batteries for the harbor defenses of Boston. This is a post by Zardoz50. He has posted similar files for forts and batteries all over the world.

 

You can then view the file in Google Earth. In Google Earth just click on file>open then select the file.

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Thank you all!

 

Dave D kindly contacted me and I sent him 16 pairs of Army grid/lat-long points which he said he would process and see if a transform between the two systems could be devised. I regret that the procedure for this is beyond me. Perhaps I could do it if I understood. I would love to understand it though, and will make an effort :anicute:

 

What I am after is a "rule" for going from the grid to lat/long, since there are a few important assets in the defense system which are only described in grid terms. I will eventually walk these places and could derive HH2 coordinates, but I was hoping for something precise (like the coords I have for all the fire control towers in the system).

 

The Google Earth map is fascinating. I don't understand KML files or how to go about making a map like this, but I could (and I think must) do this in connection with my catalog and resulting website. Is there a good way to learn this process? And do I need to pay hundreds of dollars for Google Earth (or put another way, is there a benefit to buying the "fancy" version?)? If someone would be willing to email me offline on this, I would much appreciate it.

 

The Zardoz50 map has a number of the features right, but many more mis-identified or mis-located, based upon a comparison with the sites that I have done walked myself. I should contact this person.

 

Bill93--I will look at CORPSCON and try to work with it.

 

And I guess I will have to get to understand what SPCs are! Well, I knew this would come sooner or later. B)

 

Patty--the map is such a small scale that yes, it does show all the harbor defense points I would be concerned with. But it seems to be just a schematic sketch map to accompany the overall 1945 report on the Boston HD, not a real working document. If this grid system is what they used for fire control (and I don't know yet), then they must have had scads of large scale charts built off it and used in the Plotting Rooms to actually target the guns.

 

How would I go about "calibrating" the map, given that I have my 16 "paired" points?

 

I'm really fascinated with all this and thanks a million for all the help.

 

-Paul

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Paul:

 

You may want to take a look at some of the publications from the National Geospatial-Intelligence Agency (NGA). They are the Department of Defense (DOD) experts in most things to do with maps and related materials (e.g. imagery). HERE is a good link for their public documents relating to maps.

 

Documents 2 and 3 have a lot to do with map datums, and are the basis for conversions of many worldwide & historical datums. At just a quick look, I didn't see any conversions from older Military grids, but I might have missed it. Item 5 (GEOTRANS) is the actual software to do the conversions. Might be related to the Army Corps of Engineers CORPSCON, not sure. I worked with it some, and it's relatively easy.

 

There's also some general info / training materials on Geodesy there that are pretty good.

 

They were not able to help me with my recent datum conversion project from an 1899 survey, but they were very nice about it. You might consider emailing them with your question.

 

Larry

(Klemmer)

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Another thing you might try is using your chart as an overlay on Google Earth. You can take a JPG and overlay it on Google Earth. The trick is to align the overlay.

 

Most of the time the fire control towers have horizontal benchmarks associated with them as the locations of the towers and gun emplacements were surveyed very precisely in order to make the fire control calculations as precise as possible. Many of those marks have been put into the NGS database. This helps in aligning the overlay. If you put the LatLon of the NGS marks into GE you can then use them to align the JPG.

 

The problem I see is that the map you have covers a very large area and it might be difficult to precisely align it. Maybe if you only used small sections of the chart, say one fort at a time. But then you have the problem of the accuracy of the chart its self.

 

As for Google Earth, I do all the things I mention above with the free version. I there are more features you can use with the paid version but I have not found much use for those. The hundreds of dollars version is for people like our local TV station that uses it to show the location of events in the news as well as the weather and traffic reports. Since you are not using GE for that kind of commercial use you won’t need that costly version.

 

I loves my Google Earth!

 

What is your source for your location and other info on these forts?

 

Last Saturday I got a tour of Battery DeMerritt that had 2 8” guns.

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Thank you, Larry!

 

68-Eldo: As you pointed out, all the FC towers were surveyed by USCGS and I have all these coords. The grid coords come from the RCWs (Reports of Completed Works), the standard Army Corps pf ENgineers reference for the various harbor defenses. I acquired these on DVD from the Coast Defense Study Group (CDSG).

 

Looks like I may have to figure out Google Earth. :anicute:

 

-Paul

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How would I go about "calibrating" the map, given that I have my 16 "paired" points?

I use MacGPS Pro for that myself. You can bring up any JPG, GIF, etc. image, click on a few places, tell the program what the coordinates are at those places, and it will calibrate the whole image. Then you can click on any point in the image and get its coordinates.

 

Patty

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The grid coords come from the RCWs (Reports of Completed Works), the standard Army Corps pf ENgineers reference for the various harbor defenses. I acquired these on DVD from the Coast Defense Study Group (CDSG).

OK, that does it. I’m sending in my membership application and dues. I’ve been thinking about joining but have procrastinated.

 

Thanks for the push. :)

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68-eldo:

 

There are three types of files I have received from CDSG (for a price, of course):

 

-the RCWs (these are "cards" kept by the Engineers for various locations that list their data (like

gun types, dates, and dispostion for various forts) and give plans an elevation dwgs. The dwgs on

CoastDefense.com come from here.

 

-Summary reports for each Harbor (like I bought Portland, Portsmouth, Boston and New Bedford).

The map I posted came from the Boston report in this series.

 

-Quartermaster reports- not as useful; list all the maintenance seriatum for each support bldg,

but sometimes contain photos.

 

I think I spent about $150 for all my harbors, plus the big paper bound book American Seacost Defenses, a "bible" of history, definitions, photos, etc (600pp.+). Very useful!

 

It would take 1,000s of hrs. in the National Archives to accumulate the equivalent stuff!

 

-Paul

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Most systems like this labelled as "Local Coordinates" are not on a formal projection but are based upon a true north azimuth somewhere in the area and possible false northing and easting for a given point. There is an example in the DC areas known as WSSC Coordinates which are based upon the dome of the capitol being 0/0 and true north out of there. A plane grid is then carried forward by the terrestrial surveys over time.

 

While these types of systems were not originally based on a projection, there are a number of custom projections that can be set up that will closely approximate them. Of course to "get on to " the system requires deducing the base point and getting a lat long for it, or developing a transformation between other systems and known or recovered points in the local system.

 

What software to use to do this can vary widely, and I cannot specifically recommend some, but with the proliferation of mapping programs for GPS any that allow setting up a custom projection might be made to work. Even your GPS itself probably has a custom or user projection option that can be manipulated for the purpose. Things llike OZI Explorer and a multitude of other programs also have capabilities to define custom projections.

 

I need to look at that map again, but the presence of the True Meridian near the 100,000 Easting line suggests the possibility that the origin of the system is on that line. There is usually no scale factor in these systems and if they are near sea level you would use a scale factor of 1.0000 at the origin. A mercator projection set with the central meridian at that location with a 100,000 easting and scale of 1.000 might work reasonably well over the area and is available in almost every GPS unit's user projection options.

 

- jlw

 

PS I doubt that they have anything to do with UTM, MGRS or state plane.

 

2nd PS: If someone wants to provide me a list of the coordinates as mentioned above I can try to outline a procedure to set up a user grid that will convert them for you.

Edited by jwahl

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It may be much for you.

 

But GPS Trackmaker has User defined grid in the Tools options as well as many, many other conversions.

As stated a calibration of at least 2 points-for GPS Trackmaker are needed.

Top left and bottom right.

You can the go back and forth between options and get the lat-longs.

 

Just my 0.02

 

Changed R-L

Edited by GEO*Trailblazer 1

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this forum wont let me upload the file bit you can go into Google earth and overlay the JPG

once you have the image overlay visable select the location tab in the overlay window and put these cord into it.

 

north 42 53' 4.18" east 70 19' 54.79"

 

south 41 46' 39.18" west 71 13' 4.78"

this should get you close on a geographic level

Boston Harbor local plane coord system these are usually hard to convert in to GPS coord.

 

note all GPS work in meters so you need to convert any foot measurements into meters but often you cant use the international conversion you need a survey feet meter conversion.

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An update--

 

jwahl has kindly taken up the task of producing a conversion formula to link the Army grid with NAD83 lat/long.

At present, working with about 18 coordinate system pairs, he seems to have achieved accuracy at or below the 6-inch level, and the effort to refine the tool is continuing. I am indebted to him for all the effort he has invested in this, and to all the others of you who have offered your advice. The result of jwahl's development will be a spreadsheet where you plug in X-Y coordinates and get lat/long, or v. versa. Very cool. I will provide a more detailed explanation when the work is done.

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I know I'm a bit late to this thread but any update on the spreadsheet?

 

Morgan

 

An update--

 

jwahl has kindly taken up the task of producing a conversion formula to link the Army grid with NAD83 lat/long.

At present, working with about 18 coordinate system pairs, he seems to have achieved accuracy at or below the 6-inch level, and the effort to refine the tool is continuing. I am indebted to him for all the effort he has invested in this, and to all the others of you who have offered your advice. The result of jwahl's development will be a spreadsheet where you plug in X-Y coordinates and get lat/long, or v. versa. Very cool. I will provide a more detailed explanation when the work is done.

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I know I'm a bit late to this thread but any update on the spreadsheet?

I would drop PGrig an email. Since his last post, Jerry's had family issues last summer, hence his absence on here. :(

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About the time that pgrig posted his original inquiry I did work with him via email and came up with a pretty good best fit conversion spread sheet. I used some simplistic math to do it.

 

A few months later he found documentation for the actual map projection used, but I suspect that due to errors in the survey I am probably getting about as good and possibly even better results than if I were to program the projection because I did a least squares fit to a reasonably large set of coordinate pairs and optimized my transformation over the area.

 

I have written to pgrig several times over the past year to ask how it is going, with no results.

 

I did find an article where he mentions it.

 

Wikipedia Article with mention.

 

as well as mention on his website:

 

reference sources

 

and here

 

mentioned here..

 

I would have to look back at our email dialog, but I think I had the conversion working at less than a foot at the 95% confidence level, but I don't really remember.

 

- jerry

Edited by jwahl

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I had a similar project with the coordinates of the harbor defenses of San Francisco. In my case I converted the origin point from NAD27 to NAD83 using NGS NADCON and converted the Army grid coordinates to azimuth and distance from the origin point.

 

What does "hub" refer to on a 1940's drawing?

 

 

Morgan

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Just a note to say I'm still alive and well and would be pleased to send anyone who's interested a copy of the Excel SS that Jerry designed for the harbor defenses of Boston. It plots L/L to within 3"-6", which to me is outstanding for my purposes. Here in Boston, almost all of the permanent batteries have nearby disks already in place and all the fire control towers are equipped with USCGS/Army Corps disks of their own. The SS has helped me locate the 155mm guns and some mobile elements, and there may be a few directing points (DPs) that can now be pinpointed.

-Paul

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Thanks for the copy Paul. For anyone else who is interested in this sort of thing the spreadsheet seemed to work well with the grid used for the harbor defenses of San Francisco once I updated the origin point.

 

Morgan

 

 

Just a note to say I'm still alive and well and would be pleased to send anyone who's interested a copy of the Excel SS that Jerry designed for the harbor defenses of Boston. It plots L/L to within 3"-6", which to me is outstanding for my purposes. Here in Boston, almost all of the permanent batteries have nearby disks already in place and all the fire control towers are equipped with USCGS/Army Corps disks of their own. The SS has helped me locate the 155mm guns and some mobile elements, and there may be a few directing points (DPs) that can now be pinpointed.

-Paul

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