{"id":8619,"date":"2019-05-02T03:00:02","date_gmt":"2019-05-02T01:00:02","guid":{"rendered":"http:\/\/www.sigterritoires.fr\/?p=8619"},"modified":"2019-05-02T07:46:10","modified_gmt":"2019-05-02T05:46:10","slug":"the-war-north-projection-how-to-manage-it-with-arcgis","status":"publish","type":"post","link":"https:\/\/www.sigterritoires.fr\/index.php\/en\/the-war-north-projection-how-to-manage-it-with-arcgis\/","title":{"rendered":"The War North projection, how to manage it with ArcGis."},"content":{"rendered":"\n

Origin of the War North\nprojection<\/a><\/strong> <\/p>\n\n\n\n

Here is an excerpt of the thesis defended in\nNovember 2005 by Nicolas Guilhot, currently Lecturer in History and Management\nat IFROSS – University Lyon 3, at the Graduate School of Social and Law\nSciences of LYON II University – LUMIERE. Those\nwishing to consult the full text will refer to: http:\/\/theses.univ-lyon2.fr\/documents\/lyon2\/2005\/guilhot_n<\/a>\n
\n\u00ab\u00a0As in many other areas of official\ncartography, the first world war confirmed and accentuated the current\nevolution in the projection systems used, and, even, if the preference for the\nquality of conformity was not questioned, a projection system more suitable to\nthe new military needs was adopted: the war of position and the central role of\nartillery fire according to maps had demonstrated the need for the military to\nhave, not only, geographical coordinates (degrees or grades), but also\nrectangular (kilometric) in order to obtain the coordinates of a position\ndirectly by their measurement on the map. However the polycentric system did\nnot allow assembling several sheets in a coherent system of rectangular\ncoordinates, a gap particularly problematic given the small area covered by the\nbreaks in the master plans.<\/em> During the\nwar, the SGA had adopted Lambert’s projection in 1915, a consistent modified\nconic projection.<\/em> <\/p>\n\n\n\n\n\n\n\n

In Lambert’s projection, the consistency i.e the\nconservation of the angles, required a correction that increased with the\ndistance from the average parallel chosen for the projection, which made it\nnecessary to limit the area of \u200b\u200buse of the system in the north-south direction\nto avoid excessive length alteration.<\/em> The\nLambert system adopted during the war, called the war north, was chosen to make\nan eastward extension for obvious military reasons: it could not, therefore, be\nextended to the whole of France after the end of the conflict.<\/em> However, since the use of rectangular coordinates proved\nto be also advantageous from a topographic point of view, especially for the\ndetermination of the planimetric pattern, the SGA conducted studies to adopt an\nidentical grid system on a large-scale map, 1: 20 000 or 1: 50 000, which led\nto the adoption, in 1920, of new projection systems for the whole of France.<\/em>\n<\/p>\n\n\n\n

For the same military reasons, the Lambert\nprojection, indefinitely expandable to the east, was preferred to the Gaussian projection,\na particular case of the Lambert projection that can be indefinitely stretched in\nthe north-south direction.<\/em> Due to the\nincrease in deformations with the distance from the reference parallel of the\nprojection, three different systems were adopted in France: Lambert north zone,\nLambert central zone, Lambert south zone, all referring to the ellipsoid of\nClarke (1880) and to the starting elements of the new triangulation\n(geographical position of the Pantheon and Rosny azimuth).<\/em> Tables and systems of transformation were later developed\nto, gradually, harmonize the existing sheets, but the base maps could not be\nretouched and only the coordinates indicated in the frame of the map and the\ngrid used were modified as long as the map design was not completely redone as\na result of new surveys. \u00ab\u00a0<\/em> \n\nThis\nprojection was used since the First World War until the end of the 1940s. It\ncovered part of northern France and, between the two wars; it was completed by\nthe adoption of Lambert I, II and III zones. The following figure, taken\nfrom http:\/\/www.echodelta.net: The\nprinciple of the \u00ab\u00a0Modified British\u00a0\u00bb coordinate system<\/a> shows the zones corresponding to the projections in progress\nduring the Second World War.\n\n\n\n<\/p>\n\n\n\n