Dear Mardi Seng,
I received the below communication from you via a Map Library List Service. As it happens, I spent many years in the US Government involved with international mapping and can make a few observations and recommendations for your situation.
I understand that you need to plot locations derived from modern GPS measurements (based on WG-84 datum) on top of old maps produced according to the French Indochinese Bonne projection? I suppose the border reference locations were recorded on those older maps, plus current political considerations come into play, but a more enduring and technically practical approach would be to transpose those original border locations from the older maps onto a new modern map based upon the WG-84 world datum. In any case you will need to employ the services of a skilled Geographic Information System professional, plus someone experienced and skilled in the technical analysis and interpretation of large scale topographic maps.
For your particular situation, the following articles may be of interest to the professionals I mentioned, because if full projection, datum, spheroid information is not printed on the maps, and if ArcGIS software has not captured the mathematical parameters for French Indochina mapping based on the Bonne projection, then a bit of research will be needed.
I note that the US AMS maps are produced on the Everest Spheroid, UTM projection, and horizontal datum is Indian 1960.
Please note that the AMS mapping responsibilities have now been absorbed by the US National Geospatial-Intelligence Agency (NGA). NGA may likely have current official mapping agreements with the Cambodian and Vietnamese government mapping organizations!
In any case, accurately transferring locations from one map to another can become a big mathematical challenge. Fortunately, someone has probably already tackled this challenge and captured the transformations in the leading digital mapping package: ArcGIS from ESRI in Redlands, California.
I would also suggest communicating via the US Embassy with the US Office of the Geographer at our Department of State (Foreign Ministry). It is their responsibility to collect and preserve boundary maps for all parts of the world of interest to the United States. I am sure they would take high interest in the current Cambodian/Vietnam joint effort. Maybe they would also provide some form of assistance.
Also please contact ESRI in Redlands, California:
http://www.esri.com/ ESRI’s president, Jack Dangermond, is very interested in international efforts such as yours and may provide assistance.
Best of luck and I’ll be glad to address follow-up questions you may have.
Mark S. Johnson, PMP
703-507-8008
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Responding to the following email:
My name is Mardi Seng from Cambodia and I am working on a project that requires using GPS coordinates onto the 1933-1953 French-made maps (BONNE). A group of people has been searching the parameters that would give us a link between the two projections so we can place the WGS84 datum on a very old map.
Background:
Cambodia and Vietnam are demarcating their borders using the delimited 1933-1953 French-made (1:100,000) maps. To assist with the demarcation, they are using the 1960's US (1:50,000) maps. To make a very long story short, the Vietnamese working on this delimiting/demarcating project are technically and politically much more superior than their Cambodia counterpart and the Cambodian government has been working on this project secretly without oversight or scrutiny from the National Assembly or the public.
I am working for a committee representing the National Assembly to try to provide oversight or scruitinize the demarcation process. But I am not trained in this field (I am an auditor/risk management by training) and I need to learn as much as possible in a very short time.
I am asking for your help.
1. Do you know (or anyone who would know) the parameters that link between BONNE and UTM projections?
2. Would AMS have the parameters between the two projections? When AMS made the maps of Cambodia in 1960's, AMS used the French-made maps as the basis and "transferred" to the UTM grid?
3. My understanding is that there are at least 6 different versions of the 1933-1953 French-made maps. And there are many more copies such as 1) 1960's AMS 1:50,000 maps, 2) 1970's, 1990's 1:100,000 maps but on UTM grids. IF we have to reconcile or compare the authenticity of these maps, where do we start?
I would appreciate it if I can have the opportunity to talk to you. Can I call you? Can I have your phone number?
Thank you so much for your time.
Mardi