{"id":21591,"date":"2026-07-13T11:10:21","date_gmt":"2026-07-13T09:10:21","guid":{"rendered":"https:\/\/ngi.be\/?page_id=21591"},"modified":"2026-08-21T11:53:19","modified_gmt":"2026-08-21T09:53:19","slug":"transformation-entre-systemes-de-coordonnees","status":"publish","type":"page","link":"https:\/\/ngi.be\/fr\/offre\/les-services\/services-geodesiques\/transformation-entre-systemes-de-coordonnees\/","title":{"rendered":"Transformation entre syst\u00e8mes de coordonn\u00e9es"},"content":{"rendered":"<p>La transformation de coordonn\u00e9es est une \u00e9tape essentielle en g\u00e9od\u00e9sie et en cartographie.\u00a0Elle permet de convertir des positions g\u00e9ographiques d\u2019un syst\u00e8me de r\u00e9f\u00e9rence \u00e0 un autre. Elle garantit\u00a0une\u00a0utilisation compatible, pr\u00e9cise et coh\u00e9rente des donn\u00e9es provenant de diff\u00e9rentes sources. Ceci est crucial pour\u00a0la pr\u00e9cision\u00a0de projets\u00a0utilisant des donn\u00e9es g\u00e9ospatiales comme les projets\u00a0de topographie,\u00a0d\u2019analyses\u00a0spatiales\u00a0ou de\u00a0r\u00e9alisation de\u00a0cartes num\u00e9riques.<\/p>\n<p>Un grand nombre de donn\u00e9es g\u00e9ographiques existantes en Belgique ne sont pas g\u00e9or\u00e9f\u00e9renc\u00e9es selon les syst\u00e8mes de coordonn\u00e9es de r\u00e9f\u00e9rence actuellement utilis\u00e9s comme standards.\u00a0La conversion\u00a0des coordonn\u00e9es entre les diff\u00e9rents syst\u00e8mes\u00a0de r\u00e9f\u00e9rence\u00a0peut donc s\u2019av\u00e9rer complexe.\u00a0Pour faciliter ces conversions, l\u2019IGN\u00a0met \u00e0 disposition une s\u00e9rie d\u2019outils\u00a0d\u00e9di\u00e9s.<\/p>\n<p><strong>cConvert\u00a0<\/strong><\/p>\n<p>L\u2019IGN a d\u00e9velopp\u00e9\u00a0<a href=\"https:\/\/cconvert.geo.be\/\" target=\"_blank\" rel=\"noopener\">cConvert<\/a>, une application en ligne qui permet de transformer facilement des coordonn\u00e9es entre les syst\u00e8mes de\u00a0coordonn\u00e9es\u00a0utilis\u00e9s en Belgique, comme :<\/p>\n<ul>\n<li>ETRS89 (European\u00a0Terrestrial\u00a0Reference System 1989),<\/li>\n<li>Belgian\u00a0Datum 1972,<\/li>\n<li>European\u00a0Datum 1950,<\/li>\n<li>et\u00a0leurs projections associ\u00e9es (<a href=\"https:\/\/ngi.be\/fr\/offre\/les-services\/services-geodesiques\/systemes-de-coordonnees-belges\/lambert-2008\/\" target=\"_blank\" rel=\"noopener\">Lambert 2008<\/a>,\u00a0<a href=\"https:\/\/ngi.be\/fr\/offre\/les-services\/services-geodesiques\/systemes-de-coordonnees-belges\/lambert-1972\/\" target=\"_blank\" rel=\"noopener\">Lambert 1972<\/a>, UTM, etc.).<\/li>\n<\/ul>\n<p>cConvert\u00a0accepte aussi bien des points uniques que des listes compl\u00e8tes de coordonn\u00e9es. Cette flexibilit\u00e9\u00a0simplifie grandement les traitements de donn\u00e9es g\u00e9ographiques et leur int\u00e9gration dans des logiciels SIG ou des workflows de topographie. En compl\u00e9ment de\u00a0cConvert, l\u2019IGN propose une documentation p\u00e9dagogique expliquant les principes de la conversion de coordonn\u00e9es, ainsi que des ressources de donn\u00e9es et des services g\u00e9od\u00e9siques pour accompagner vos projets cartographiques.<\/p>\n<p><strong>Coordonn\u00e9es GNSS : ITRS,\u00a0WGS 84 ou ETRS89\u202f?<\/strong><\/p>\n<p>Pour des raisons historiques, la plupart des utilisateurs pensent obtenir des coordonn\u00e9es en WGS\u00a084 lorsqu\u2019ils d\u00e9terminent une position \u00e0 l\u2019aide de satellites de navigation. Cette affirmation n\u2019est toutefois pas enti\u00e8rement correcte.\u00a0Les diff\u00e9rentes constellations\u00a0de satellites (GPS, Galileo, GLONASS et\u00a0BeiDou) expriment chacune leur position dans leur propre syst\u00e8me\u00a0de coordonn\u00e9es global, mais sont toutes align\u00e9es, conform\u00e9ment \u00e0 un accord international, sur\u00a0<b>l\u2019International\u00a0Terrestrial\u00a0Reference\u00a0System\u00a0<\/b>(ITRS). Un utilisateur standard de satellites de navigation d\u00e9termine donc sa position en ITRS et non en WGS\u00a084.<\/p>\n<p>L\u2019utilisation d\u2019un syst\u00e8me de coordonn\u00e9es global est par ailleurs peu pratique dans un contexte g\u00e9od\u00e9sique national. En raison de la d\u00e9rive des continents,\u00a0la plaque continentale europ\u00e9enne se d\u00e9place chaque ann\u00e9e d\u2019environ 2,5 cm vers le nord-est.\u00a0Les coordonn\u00e9es exprim\u00e9es dans un syst\u00e8me global tel que l\u2019ITRS sont\u00a0donc\u00a0dynamiques : elles\u00a0changent chaque ann\u00e9e. Or, pour r\u00e9aliser des mesures g\u00e9om\u00e9triques pr\u00e9cises et comparables\u00a0entre elles, un syst\u00e8me de coordonn\u00e9es statique est indispensable.<\/p>\n<p>En Europe, la solution adopt\u00e9e est l\u2019<b>ETRS89<\/b> (European\u00a0Terrestrial\u00a0Reference System 1989).\u00a0L\u2019ETRS89\u00a0est<b><\/b> align\u00e9 \u00e0 l\u2019origine sur l\u2019ITRS,\u00a0mais fix\u00e9 \u00e0 la plaque eurasienne, ce qui garantit la stabilit\u00e9 des coordonn\u00e9es sur le territoire belge dans le temps.\u00a0Les mesures GNSS en mode RTK (temps r\u00e9el), bas\u00e9es sur les signaux de correction transmis par les r\u00e9seaux de positionnement\u00a0comme\u00a0FLEPOS, WALCORS ou\u00a0GPSBRU, fournissent des positions directement exprim\u00e9es en ETRS89.<\/p>\n<p>La diff\u00e9rence entre les coordonn\u00e9es ETRS89 et WGS 84 est d\u2019environ 1 m\u00e8tre en 2026 et augmente d\u2019environ 2,5 cm chaque ann\u00e9e. Les applications moins exigeantes en pr\u00e9cision assimilent souvent l\u2019ETRS89 au WGS 84, bien qu\u2019il s\u2019agisse en r\u00e9alit\u00e9 de syst\u00e8mes distincts.\u202fVous trouverez plus d\u2019informations \u00e0 ce sujet sur la page \u00ab\u202f<a href=\"https:\/\/ngi.be\/fr\/offre\/les-services\/services-geodesiques\/du-gps-au-gnss\/\" target=\"_blank\" rel=\"noopener\">Du GPS au GNSS<\/a>\u202f\u00bb.<\/p>\n<p><strong>Transformation Lambert\u00a01972 &#8211; Lambert 2008<\/strong><\/p>\n<p>La transformation entre les syst\u00e8mes de coordonn\u00e9es Lambert\u00a01972 et Lambert 2008 ne se fait pas directement\u00a0via une\u00a0simple formule de\u00a0conversion.\u00a0\u00a0En raison de\u00a0d\u00e9formations\u00a0survenues lors de la cr\u00e9ation du r\u00e9seau Lambert 1972,\u00a0un ensemble d\u2019\u00e9tapes successives\u00a0doit \u00eatre suivi\u00a0afin de garantir la pr\u00e9cision :<\/p>\n<ol>\n<li>Application d\u2019une grille de correction n\u00e9cessaire pour la prise en compte des d\u00e9formations cr\u00e9\u00e9es lors de l\u2019\u00e9tablissement du Lambert\u00a01972<\/li>\n<li>D\u00e9projection\u00a0de\u00a0Lambert<\/li>\n<li>Transformation des\u00a0coordonn\u00e9es\u00a0g\u00e9ographiques\u00a0en coordonn\u00e9es g\u00e9ocentriques<\/li>\n<li>Modification du\u00a0datum\u00a0g\u00e9od\u00e9sique \u00e0 l\u2019aide des param\u00e8tres\u00a0de\u00a0Helmert ci-dessous<\/li>\n<li>Conversion des\u00a0coordonn\u00e9es\u00a0g\u00e9ocentriques en coordonn\u00e9es g\u00e9ographiques<\/li>\n<li>Projection\u00a0de\u00a0Lambert<\/li>\n<\/ol>\n<p><strong>Param\u00e8tres de conversion de\u00a0Helmert\u202f(LB72\u00a0\u00e0\u00a0LB08)\u202f:<\/strong><\/p>\n<table border=\"1\" width=\"605\" cellspacing=\"0\" cellpadding=\"5\">\n<tbody>\n<tr>\n<td width=\"180\"><strong>Param\u00e8tre<\/strong><\/td>\n<td width=\"180\"><strong>Valeur<\/strong><\/td>\n<\/tr>\n<tr>\n<td>Delta\u00a0X \u2013\u00a0(m)<\/td>\n<td>106,869<\/td>\n<\/tr>\n<tr>\n<td>Delta\u00a0Y \u2013\u00a0\u0394y\u00a0(m)<\/td>\n<td>\u221252,298<\/td>\n<\/tr>\n<tr>\n<td>Delta\u00a0Z \u2013\u00a0\u0394z\u00a0(m)<\/td>\n<td>33,724<\/td>\n<\/tr>\n<tr>\n<td>Rotation\u00a0X \u2013\u00a0(&#8220;)<\/td>\n<td>0,33657<\/td>\n<\/tr>\n<tr>\n<td>Rotation\u00a0Y \u2013 Ry (&#8220;)<\/td>\n<td>\u22120,456955<\/td>\n<\/tr>\n<tr>\n<td>Rotation\u00a0Z \u2013\u00a0Rz\u00a0(&#8220;)<\/td>\n<td>-1,842183<\/td>\n<\/tr>\n<tr>\n<td>Facteur d\u2019\u00e9chelle\u00a0\u2013 1+s<\/td>\n<td>1,0000012747<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>L\u2019IGN attire l\u2019attention sur le fait\u00a0que tous les logiciels de transformation n\u2019incluent\u00a0pas\u00a0n\u00e9cessairement\u00a0la grille de correction reprise \u00e0 l\u2019\u00e9tape 1,\u00a0ce qui peut entra\u00eener des distorsions importantes. C\u2019est pourquoi\u00a0l\u2019utilisation de\u00a0cConvert\u00a0est recommand\u00e9e, car cette application int\u00e8gre la grille de correction.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-21822\" src=\"https:\/\/ngi.be\/app\/uploads\/2026\/07\/lambert_schema_700_euref-1024x871.png\" alt=\"\" width=\"850\" height=\"723\" srcset=\"https:\/\/ngi.be\/app\/uploads\/2026\/07\/lambert_schema_700_euref-1024x871.png 1024w, https:\/\/ngi.be\/app\/uploads\/2026\/07\/lambert_schema_700_euref-300x255.png 300w, https:\/\/ngi.be\/app\/uploads\/2026\/07\/lambert_schema_700_euref-768x654.png 768w, https:\/\/ngi.be\/app\/uploads\/2026\/07\/lambert_schema_700_euref-1536x1307.png 1536w, https:\/\/ngi.be\/app\/uploads\/2026\/07\/lambert_schema_700_euref-220x187.png 220w, https:\/\/ngi.be\/app\/uploads\/2026\/07\/lambert_schema_700_euref-411x350.png 411w, https:\/\/ngi.be\/app\/uploads\/2026\/07\/lambert_schema_700_euref.png 1920w\" sizes=\"auto, (max-width: 850px) 100vw, 850px\" \/><\/p>\n<p><strong>Transformation dans un logiciel SIG<\/strong><\/p>\n<p>La transformation d\u00e9crite ci-dessus ne peut \u00eatre appliqu\u00e9e\u00a0directement\u00a0dans un logiciel SIG tel que QGIS,\u00a0ArcGis, ArcMap, AutoCAD, \u2026 Dans ce cas, il faut utiliser\u00a0la\u00a0grille NTv2 qui correspond\u00a0\u00e0 une grille binaire permettant la transformation via 347 225 n\u0153uds d\u00e9velopp\u00e9e par Nicolas Simon (SPW).\u00a0Les \u00e9carts avec les r\u00e9sultats dans\u00a0cConvert ne sont de quelques millim\u00e8tres.<\/p>\n<p><strong>Param\u00e8tres fondamentaux des projections Lambert 1972 et Lambert\u00a02008<\/strong><\/p>\n<p>Le tableau ci-dessous pr\u00e9sente les param\u00e8tres fondamentaux des deux projections.<\/p>\n<table border=\"1\" width=\"605\" cellspacing=\"0\" cellpadding=\"5\">\n<tbody>\n<tr aria-rowindex=\"1\">\n<td data-celllook=\"69905\"><b>Param\u00e8tre<\/b><\/td>\n<td data-celllook=\"69905\"><\/td>\n<td data-celllook=\"69905\"><\/td>\n<td data-celllook=\"69905\"><\/td>\n<\/tr>\n<tr aria-rowindex=\"2\">\n<td data-celllook=\"69905\">Ellipso\u00efde<\/td>\n<td data-celllook=\"69905\">Nom<\/td>\n<td data-celllook=\"69905\">Hayford\u00a01924<\/td>\n<td data-celllook=\"69905\">GRS80<\/td>\n<\/tr>\n<tr aria-rowindex=\"3\">\n<td data-celllook=\"69905\"><\/td>\n<td data-celllook=\"69905\">Demi-grand axe (a)<\/td>\n<td data-celllook=\"69905\">6.378.388,0 m<\/td>\n<td data-celllook=\"69905\">6.378.137,0 m<\/td>\n<\/tr>\n<tr aria-rowindex=\"4\">\n<td data-celllook=\"69905\"><\/td>\n<td data-celllook=\"69905\">Coefficient d\u2019aplatissement (f)<\/td>\n<td data-celllook=\"69905\">1 \/\u00a0297,0<\/td>\n<td data-celllook=\"69905\">1 \/\u00a0298,257222101<\/td>\n<\/tr>\n<tr aria-rowindex=\"5\">\n<td data-celllook=\"69905\">Parall\u00e8les s\u00e9cants<\/td>\n<td data-celllook=\"69905\">\u03c6<sub>\u2081<\/sub><\/td>\n<td data-celllook=\"69905\">49\u00b0 50&#8242; 00&#8243; N<\/td>\n<td data-celllook=\"69905\">49\u00b0 50&#8242; N<\/td>\n<\/tr>\n<tr aria-rowindex=\"6\">\n<td data-celllook=\"69905\"><\/td>\n<td data-celllook=\"69905\">\u03c6<sub>\u2082<\/sub><\/td>\n<td data-celllook=\"69905\">51\u00b0 10&#8242; 00&#8243; N<\/td>\n<td data-celllook=\"69905\">51\u00b0 10&#8242; N<\/td>\n<\/tr>\n<tr aria-rowindex=\"7\">\n<td data-celllook=\"69905\">Origine<\/td>\n<td data-celllook=\"69905\">Latitude origine<\/td>\n<td data-celllook=\"69905\">90\u00b0<\/td>\n<td data-celllook=\"69905\">50\u00b0 47&#8242; 52.134&#8243; N<\/td>\n<\/tr>\n<tr aria-rowindex=\"8\">\n<td data-celllook=\"69905\"><\/td>\n<td data-celllook=\"69905\">M\u00e9ridien central<\/td>\n<td data-celllook=\"69905\">4\u00b0 22&#8242; 02.952&#8243; E<\/td>\n<td data-celllook=\"69905\">4\u00b0 21&#8242; 33.177&#8243; E<\/td>\n<\/tr>\n<tr aria-rowindex=\"9\">\n<td data-celllook=\"69905\">Fausse origine \u2013 translation en abscisse et en ordonn\u00e9e<\/td>\n<td data-celllook=\"69905\">x<sub>\u2080<\/sub><\/td>\n<td data-celllook=\"69905\">150.000,013 m<\/td>\n<td data-celllook=\"69905\">649.328,0 m<\/td>\n<\/tr>\n<tr aria-rowindex=\"10\">\n<td data-celllook=\"69905\"><\/td>\n<td data-celllook=\"69905\">y<sub>\u2080<\/sub><\/td>\n<td data-celllook=\"69905\">5.400.088,438 m<\/td>\n<td data-celllook=\"69905\">665.262,0 m<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><strong>Transformation Lambert 50 &#8211; Lambert\u00a019<\/strong><\/p>\n<p>Il n\u2019existe pas de\u00a0transformation unique entre la projection Lambert 1950 et la projection Lambert 1972\u00a0applicable \u00e0 l\u2019ensemble du territoire belge. Cela est d\u00fb aux techniques de mesures utilis\u00e9es \u00e0 l\u2019\u00e9poque pour la triangulation du Lambert\u00a01950\u202f: la pr\u00e9cision et l\u2019homog\u00e9n\u00e9it\u00e9 du r\u00e9seau de\u00a0mesure varient consid\u00e9rablement.<\/p>\n<p>Cependant, il est possible d\u2019approximer une formule de transformation\u00a0locale en comparant, au sein d\u2019une zone de projet d\u00e9limit\u00e9e,\u00a0un nombre de points\u00a0dont les coordonn\u00e9es sont\u00a0connues\u00a0\u00e0 la fois\u00a0en\u00a0Lambert 1950 et\u00a0en\u00a0Lambert 1972.\u00a0La qualit\u00e9 de\u00a0la transformation obtenue d\u00e9pend de la densit\u00e9 et de la r\u00e9partition des points de r\u00e9f\u00e9rence disponibles dans la zone \u00e9tudi\u00e9e.<br \/>\nSur demande, l\u2019IGN peut fournir une formule de conversion propre \u00e0 votre zone d\u2019\u00e9tude. Pour cela, envoyez\u00a0votre\u00a0liste de points\u00a0ou la coordonn\u00e9e du centre de votre projet\u00a0au format ci-dessous \u00e0\u00a0<a href=\"mailto:gdoc@ngi.be\" target=\"_blank\" rel=\"noopener\">gdoc@ngi.be<\/a>.<\/p>\n<p><strong>Format\u00a0demand\u00e9\u00a0<\/strong><\/p>\n<p>Format de fichier : .txt<\/p>\n<p>Nom du document : {AAAA.MM.JJ}_{NOM}_REQUEST.txt<\/p>\n<p>S\u00e9parateur : virgule\u00a0( ,\u00a0)<\/p>\n<p>S\u00e9parateur d\u00e9cimal : point\u00a0( .\u00a0)<\/p>\n<p><strong>En-t\u00eate\u00a0<\/strong><\/p>\n<p>NBR,x50,y50<\/p>\n<p><strong>Exemple de\u00a0format\u00a0de donn\u00e9es :\u00a0<\/strong><\/p>\n<p>POINT1,159253.76,235696.13<\/p>\n<p><strong>Exemple\u00a0de\u00a0nom du fichier\u202f:\u00a0<\/strong><\/p>\n<p>2024.03.14_DUPONT_REQUEST.txt<\/p>\n<p><a href=\"https:\/\/ngi.be\/app\/uploads\/2026\/08\/2024.03.14_DUPONT_REQUEST.txt\" download=\"yyyy.mm.dd_NAME_REQUEST.txt\">T\u00e9l\u00e9chargez le mod\u00e8le ici.<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>La transformation de coordonn\u00e9es est une \u00e9tape essentielle en g\u00e9od\u00e9sie et en cartographie.\u00a0Elle permet de convertir des positions g\u00e9ographiques d\u2019un syst\u00e8me de r\u00e9f\u00e9rence \u00e0 un autre. Elle garantit\u00a0une\u00a0utilisation compatible, pr\u00e9cise et coh\u00e9rente des donn\u00e9es provenant de diff\u00e9rentes sources. Ceci est crucial pour\u00a0la pr\u00e9cision\u00a0de projets\u00a0utilisant des donn\u00e9es g\u00e9ospatiales comme les projets\u00a0de topographie,\u00a0d\u2019analyses\u00a0spatiales\u00a0ou de\u00a0r\u00e9alisation de\u00a0cartes num\u00e9riques. Un&#8230;<\/p>\n","protected":false},"author":19,"featured_media":0,"parent":656,"menu_order":12,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"footnotes":""},"class_list":["post-21591","page","type-page","status-publish","hentry"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.6 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Transformation entre syst\u00e8mes de coordonn\u00e9es - IGN<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/ngi.be\/fr\/offre\/les-services\/services-geodesiques\/transformation-entre-systemes-de-coordonnees\/\" \/>\n<meta property=\"og:locale\" content=\"fr_FR\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Transformation entre syst\u00e8mes de coordonn\u00e9es - IGN\" \/>\n<meta property=\"og:description\" content=\"La transformation de coordonn\u00e9es est une \u00e9tape essentielle en g\u00e9od\u00e9sie et en cartographie.\u00a0Elle permet de convertir des positions g\u00e9ographiques d\u2019un syst\u00e8me de r\u00e9f\u00e9rence \u00e0 un autre. Elle garantit\u00a0une\u00a0utilisation compatible, pr\u00e9cise et coh\u00e9rente des donn\u00e9es provenant de diff\u00e9rentes sources. Ceci est crucial pour\u00a0la pr\u00e9cision\u00a0de projets\u00a0utilisant des donn\u00e9es g\u00e9ospatiales comme les projets\u00a0de topographie,\u00a0d\u2019analyses\u00a0spatiales\u00a0ou de\u00a0r\u00e9alisation de\u00a0cartes num\u00e9riques. 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