[Proj] Map projection of Portugal

Clifford J Mugnier cjmce at lsu.edu
Tue Dec 31 17:41:02 EST 2013


Plane coordinate systems comprised of quadrants with plus & minus signs associated with coordinate components were common in Europe and many European colonies in the 19th century and some hold-overs remained during the first half of the 20th century.  With regard to the "Great War," (WWI), the French Kilometric Quadrillage used specifically in the Nord de Guerre Zone of Northern France and Belgium was the primary inspiration for the American series of the State Plane Coordinate Systems.  After WWII, projection tables were published for all of the American states and territories specifically for the land aeras.  Little thought was given to developing geodetic plane coordinate systems for offshore areas of American territorial waters.

Metal welding technologies advanced such that stiff-leg platforms were fabricated and moved offshore into the Gulf of Mexico to enable oil exploration and production activities.  Over time, the platforms started being emplaced further and further offshore.  Eventually, the offshore lease blocks began being used that were far south of the False Origin of the Louisiana South (1702) Zone, and from time-to-time Licensed Surveyors would "forget" the minus sign on the Y-coordinate and the platform would be placed exactly on the X-coordinate but 20 miles or so too far north of the intended location.  The economic consequences were disasterous for all concerned, as one would expect.

The use of GPS for precise positioning offshore seems to have alleviated that problem.

Minus signs on coordinates and humans don't seem to mix very well.

Clifford J. Mugnier, c.p., c.m.s.

Chief of Geodesy

LSU Center for GeoInformatics (ERAD 266)

Dept. of Civil Engineering (P.F. Taylor 3531)


Baton Rouge, LA  70803

Academic: (225) 578-8536

Research: (225) 578-4578

Cell:             (225) 328-8975

honorary lifetime member, lsps

fellow emeritus, asprs

member, apsg

From: proj-bounces at lists.maptools.org <proj-bounces at lists.maptools.org> on behalf of Jose Gonçalves <jagoncal at gmail.com>
Sent: Monday, December 30, 2013 6:39 PM
To: PROJ.4 and general Projections Discussions
Subject: [Proj] Map projection of Portugal

Dear members of the list

I would like to put some questions related to map projections being used in Europe. Most of the European countries are now using map coordinate systems based on the ETRS89 datum. The Portuguese Geographical Institute has adopted in 2006, for the continental Portugal, a projection, called “PT-TM06” (EPSG code 3763), similar to the ones used before with older geodetic datums (Datum Lisboa and Datum 73). It has, in my opinion, some annoying characteristics that make users loose time, and even make errors with costly consequences.

The projection is a transverse Mercator, with a central point in the centre of the country, no scale change, i.e. k_0=1, and no false easting/northing, so coordinates can be positive or negative. Some old coordinate systems in other countries also had the origin inside the country or region, but I think that now, most of them do not have this situation. So, my first question is if anyone knows of map coordinate systems in use, for topographic surveying and cadastre, which have negative coordinates.

The second bad aspect of our new coordinate system is that, being the projection similar to the older ones, coordinates are also very similar. Differences are in general smaller than 6 meters, so when one looks at a coordinate pair it is not obvious if it is EPSG:3763 or older systems (datum 73, EPSG:27493 or datum Lisboa, EPSG:20791). For many years people will have to deal with data in the older systems, so making mistakes becomes very easy. The reasonable approach would have been to add a big shift so that coordinates are not mistaken, as I think most countries do. This leads to my second question: does anyone know of similar situations of very close coordinate systems?
I know that in Belgium a projection was established for ETRS89 (Belge 2005, EPSG:3447) which had coordinates similar to an older system (EPSG:31300). Meanwhile a new system was defined with new false easting/northing (Belge 2008, EPSG:3812). Was the change motivated by users?

Regards and a happy new year

Jose’ Gonçalves

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