IGNF register and shift grid NTF-RGF93 - Revision history

⚠️Thibault.lemaitre: update : updating from the french translation

2011-01-03T11:55:24Z

update : updating from the french translation

← Older revision		Revision as of 11:55, 3 January 2011
Line 57:		Line 57:

	To be sure your location is well defined, repeat the step of the section [[#Problem_description\|Problem description]].		To be sure your location is well defined, repeat the step of the section [[#Problem_description\|Problem description]].
	*If you have a difference lower than 1 cm, it's ok		*If you have a difference lower than 1 cm, it's ok.
	*Otherwise, it means the shift grid is not well taken in account. Please use the [[Talk:IGNF_register_and_shift_grid_NTF-RGF93\|~~Discussion~~ tab of this page]].		*Otherwise, it means the shift grid is not well taken in account. Please use the [[Talk:IGNF_register_and_shift_grid_NTF-RGF93\|discussion tab of this page]] to report your problems.

	== Links ==		== Links ==
	[http://www.epsg-registry.org/ http://www.epsg-registry.org/]		[http://www.epsg-registry.org/ http://www.epsg-registry.org/]

	[http://lambert93.ign.fr http://lambert93.ign.fr (fr)] : site on the new French geodetic system RGF		[http://lambert93.ign.fr http://lambert93.ign.fr (fr)] : IGN's site on the new French geodetic system RGF

⚠️Thibault.lemaitre: update : updating from the french translation

2011-01-03T11:36:36Z

update : updating from the french translation

⚠️Thibault.lemaitre: /* Define a GRASS location using the shift grid */ add the note on the administrator rights

2011-01-03T10:27:02Z

Define a GRASS location using the shift grid: add the note on the administrator rights

← Older revision		Revision as of 10:27, 3 January 2011
Line 48:		Line 48:
	gksudo ln -s /usr/share/proj/ntf_r93.gsb /usr/lib/grass64/etc/nad/ntf_r93.gsb		gksudo ln -s /usr/share/proj/ntf_r93.gsb /usr/lib/grass64/etc/nad/ntf_r93.gsb
	</blockquote>		</blockquote>
	For the Windows users~~, that~~'s something like C://Program Files/grass64/etc/nad/.		Note that you must have the administrator rights to do this on Linux
			For the Windows users you don't need to be an administrator and the folder is something like C://Program Files/grass64/etc/nad/.

	If we continue with the previous projection NTF Lambert 2 étendue, which corresponds with the GRASS location NTF_L2E in my case, the file PROJ_INFO is in the folder grassdata/NTF_L2E/PERMANENT/. Open this file with a text editor. For the Linux users, add the following line at the end of the file :		If we continue with the previous projection NTF Lambert 2 étendue, which corresponds with the GRASS location NTF_L2E in my case, the file PROJ_INFO is in the folder grassdata/NTF_L2E/PERMANENT/. Open this file with a text editor. For the Linux users, add the following line at the end of the file :

⚠️Thibault.lemaitre: /* Define a GRASS location using the shift grid */ add the possibility to do a link

2010-12-02T15:11:33Z

Define a GRASS location using the shift grid: add the possibility to do a link

← Older revision		Revision as of 15:11, 2 December 2010
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	We will here show how to use the IGN shift grid for a specified GRASS location. For this, we will put the grid in a place where GRASS can use it and modify the file PROJ_INFO in the folder of the mapset PERMANENT.		We will here show how to use the IGN shift grid for a specified GRASS location. For this, we will put the grid in a place where GRASS can use it and modify the file PROJ_INFO in the folder of the mapset PERMANENT.

	First, you have to place the grid in the folder etc/nad/ of GRASS. For example, with the version 6.4 on Linux, the concerned folder is /usr/lib/grass64/etc/nad/. You can ~~do this~~ with this command :		First, you have to place the grid in the folder etc/nad/ of GRASS. For example, with the version 6.4 on Linux, the concerned folder is /usr/lib/grass64/etc/nad/. You can also create a link instead of a copy with this command :
	<blockquote>		<blockquote>
	gksudo ln -s /usr/share/proj/ntf_r93.gsb /usr/lib/grass64/etc/nad/ntf_r93.gsb		gksudo ln -s /usr/share/proj/ntf_r93.gsb /usr/lib/grass64/etc/nad/ntf_r93.gsb
Line 58:		Line 58:
	*If you have a difference lower than 1 cm, it's ok		*If you have a difference lower than 1 cm, it's ok
	*Otherwise, it means the shift grid is not well taken in account. Please use the [[Talk:IGNF_register_and_shift_grid_NTF-RGF93\|Discussion tab of this page]].		*Otherwise, it means the shift grid is not well taken in account. Please use the [[Talk:IGNF_register_and_shift_grid_NTF-RGF93\|Discussion tab of this page]].


	== Links ==		== Links ==

⚠️Thibault.lemaitre: correction and updating

2010-11-30T16:23:08Z

correction and updating

← Older revision		Revision as of 16:23, 30 November 2010
Line 3:		Line 3:
	This page describes how to well use the projections defined by the French company [http://en.wikipedia.org/wiki/Institut_G%C3%A9ographique_National IGN] in GRASS.		This page describes how to well use the projections defined by the French company [http://en.wikipedia.org/wiki/Institut_G%C3%A9ographique_National IGN] in GRASS.

	The French company IGN manages the projections used in France and provides the IGNF register, which defined them in details. The IGN also provides a shift grid for the transformations between the French geodetic systems NTF and RGF93. The French projections defined by the EPSG codes are not exactly the same than those defined by the IGN. ~~If you use the EPSG codes instead~~ of ~~the IGN specifications you can encounter an error of more or less 2~~ m.		The French company IGN manages the projections used in France and provides the IGNF register, which defined them in details. The IGN also provides a shift grid for the transformations between the French geodetic systems NTF and RGF93. The French projections defined by the EPSG codes are not exactly the same than those defined by the IGN. The difference varies between 2 cm and 5 m, with a mean value of 1,3 m.


Line 14:		Line 14:
	#Open GRASS in one of these locations and define some points. Project them to the other location with GRASS.		#Open GRASS in one of these locations and define some points. Project them to the other location with GRASS.
	#Do the same conversion with Circé.		#Do the same conversion with Circé.
	#Compare the results obtained with GRASS and Circé : you will see an abnormal difference (between -2 and +4 meters for me).		#Compare the results obtained with GRASS and Circé : you will see an abnormal difference (between 2 cm and 5 meters for me).

	The example was here with two particular EPSG codes, but this problem occurs each time you have to do a transformation between the geodetic systems NTF and RGF.		The example was here with two particular EPSG codes, but this problem occurs each time you have to do a transformation between the geodetic systems NTF and RGF.

	There is then 2 cases :		There is then 2 cases :
	*If the previous difference is negligible for your work, you can continue to use the previous defined locations as they are actually. However, don't forget that you have this ~~error~~ in each of your transformation.		*If the previous difference is negligible for your work, you can continue to use the previous defined locations as they are actually. However, don't forget that you have this difference in each of your transformation.
	*If this difference is too important for your application, follow the next steps to obtain a precision comparable to Circé.		*If this difference is too important for your application, follow the next steps to obtain a precision comparable to Circé.

Line 42:		Line 42:

	== Define a GRASS location using the shift grid==		== Define a GRASS location using the shift grid==
	We will here show how to use the IGN shift grid for a specified GRASS location. For this, we will modify the file PROJ_INFO in the folder of the mapset PERMANENT.		We will here show how to use the IGN shift grid for a specified GRASS location. For this, we will put the grid in a place where GRASS can use it and modify the file PROJ_INFO in the folder of the mapset PERMANENT.

			First, you have to place the grid in the folder etc/nad/ of GRASS. For example, with the version 6.4 on Linux, the concerned folder is /usr/lib/grass64/etc/nad/. You can do this with this command :
			<blockquote>
			gksudo ln -s /usr/share/proj/ntf_r93.gsb /usr/lib/grass64/etc/nad/ntf_r93.gsb
			</blockquote>
			For the Windows users, that's something like C://Program Files/grass64/etc/nad/.

	If we continue with the previous projection NTF Lambert 2 étendue, which corresponds with the GRASS location NTF_L2E in my case, the file PROJ_INFO is in the folder grassdata/NTF_L2E/PERMANENT/. Open this file with a text editor. For the Linux users, add the following line at the end of the file :		If we continue with the previous projection NTF Lambert 2 étendue, which corresponds with the GRASS location NTF_L2E in my case, the file PROJ_INFO is in the folder grassdata/NTF_L2E/PERMANENT/. Open this file with a text editor. For the Linux users, add the following line at the end of the file :
	<blockquote>		<blockquote>
	nadgrids: ~~/usr/share/proj/~~ntf_r93.gsb		nadgrids: ntf_r93.gsb
	</blockquote>		</blockquote>

	~~For the other users, place the shift grid file in a folder of your choice. You have then to change "/usr/share/proj/" by the path of the folder you have chosen.~~

	To be sure your location is well defined, repeat the step of the section [[#Problem_description\|Problem description]].		To be sure your location is well defined, repeat the step of the section [[#Problem_description\|Problem description]].
	*If you have a difference lower than 1 cm, it's ok		*If you have a difference lower than 1 cm, it's ok
	*Otherwise, it means the shift grid is not well taken in account. Please use the Discussion tab of this page ~~to ask the writer of this page~~		*Otherwise, it means the shift grid is not well taken in account. Please use the [[Talk:IGNF_register_and_shift_grid_NTF-RGF93\|Discussion tab of this page]].

⚠️Thibault.lemaitre: moved IGNF register and shift grid NTF/RGF93 to IGNF register and shift grid NTF-RGF93: deletion of the character "/"

2010-11-30T10:56:42Z

moved IGNF register and shift grid NTF/RGF93 to IGNF register and shift grid NTF-RGF93: deletion of the character "/"

← Older revision		Revision as of 10:56, 30 November 2010
(No difference)

⚠️Thibault.lemaitre: deletion of the translate template

2010-11-30T10:53:04Z

deletion of the translate template

← Older revision		Revision as of 10:53, 30 November 2010
Line 1:		Line 1:
	~~{{Trans\|French\|English}}~~
	[[Category:Tutorial]]		[[Category:Tutorial]]

⚠️Thibault.lemaitre: Completion of the page. Need relecture. Tests are also welcome

2010-11-17T18:42:27Z

Completion of the page. Need relecture. Tests are also welcome

← Older revision		Revision as of 18:42, 17 November 2010
Line 1:		Line 1:
	{{~~ToModify~~}}		{{Trans\|French\|English}}
			[[Category:Tutorial]]

	This page describes how to well use the projections defined by the French company ~~IGN~~ [http://en.wikipedia.org/wiki/Institut_G%C3%A9ographique_National ~~(en)] [http://fr.wikipedia.org/wiki/Institut_g%C3%A9ographique_national_%28France%29 (fr)~~] in GRASS.		This page describes how to well use the projections defined by the French company [http://en.wikipedia.org/wiki/Institut_G%C3%A9ographique_National IGN] in GRASS.

	~~In fact the~~ French company IGN manages the projections used in France and ~~defined them by~~ the IGNF register. The IGN also provides a shift grid for the French geodetic systems NTF and RGF93. The French projections defined by the EPSG codes are not exactly the same than those defined by the IGN. If you use the EPSG codes instead of the IGN specifications you can encounter an error of more or less 2 m.		The French company IGN manages the projections used in France and provides the IGNF register, which defined them in details. The IGN also provides a shift grid for the transformations between the French geodetic systems NTF and RGF93. The French projections defined by the EPSG codes are not exactly the same than those defined by the IGN. If you use the EPSG codes instead of the IGN specifications you can encounter an error of more or less 2 m.


	== Problem description ==		== Problem description ==
	The application [http://geodesie.ign.fr/index.php?page=circe Circé] is used as a reference concerning conversions between the French projection systems. We will use it to show the problem ~~defined in the introduction~~.		The application [http://geodesie.ign.fr/index.php?page=circe Circé] is used as a reference concerning conversions between the French projection systems. We will use it to show the problem previously introduced.

			The Linux users can install and use Circé with [http://en.wikipedia.org/wiki/Wine_%28software%29 Wine].

	#Define two GRASS locations with the EPSG code 2154 (for the projection RGF Lambert-93) and 27572 (for the projection NTF Lambert 2 étendue).		#Define two GRASS locations with the EPSG code 2154 (for the projection RGF Lambert-93) and 27572 (for the projection NTF Lambert 2 étendue).
Line 14:		Line 17:
	#Compare the results obtained with GRASS and Circé : you will see an abnormal difference (between -2 and +4 meters for me).		#Compare the results obtained with GRASS and Circé : you will see an abnormal difference (between -2 and +4 meters for me).

	The example was here with two particular EPSG codes, but this problem occurs each time you have to do a transformation between the geodetic systems NTF and ~~the~~ RGF.		The example was here with two particular EPSG codes, but this problem occurs each time you have to do a transformation between the geodetic systems NTF and RGF.

	There is then 2 cases :		There is then 2 cases :
	*If the previous difference is negligible for your work, you can continue to use the previous defined locations as they are actually. However, don't forget that you have this error in each of your transformation.		*If the previous difference is negligible for your work, you can continue to use the previous defined locations as they are actually. However, don't forget that you have this error in each of your transformation.
	*If this difference is too important for your application, follow the next ~~step~~ to obtain a precision comparable to Circé.		*If this difference is too important for your application, follow the next steps to obtain a precision comparable to Circé.


	== Get the register and the grid ==		== Get the register and the shift grid ==
	For the Linux users, once you have installed GRASS, you can find the register and the grid on your computer. The register is named IGNF and is in the folder /usr/share/proj/. The grid is in the same folder and is named ntf_r93.gsb.		For the Linux users, once you have installed GRASS, you can find the register and the grid on your computer. The register is named IGNF and is in the folder /usr/share/proj/. The grid is in the same folder and is named ntf_r93.gsb.

	For the ~~non Linux~~ users, or if you don't find the file on your computer, you can ~~download and~~ save [http://lambert93.ign.fr/fileadmin/files/IGNF the register] and [http://lambert93.ign.fr/fileadmin/files/ntf_r93.gsb the grid] on your computer.		For the other users, or if you don't find the file on your computer, you can save [http://lambert93.ign.fr/fileadmin/files/IGNF the register] and [http://lambert93.ign.fr/fileadmin/files/ntf_r93.gsb the grid] on your computer.


			== Differences between IGNF register and EPSG code ==
			Open the IGNF register with a text editor and search for "<LAMBE>". You will then read the informations about the previous quoted projection NTF Lambert 2 étendue, which as the code LAMBE in the IGNF register. Below, a copy of these informations.

			<blockquote>
			<LAMBE> +title=Lambert II etendu +proj=lcc '''+nadgrids=ntf_r93.gsb,null''' +towgs84=-168.0000,-60.0000,320.0000 +a=6378249.2000 +rf=293.4660210000000 +pm=2.337229167 +lat_0=46.800000000 +lon_0=0.000000000 +k_0=0.99987742 +lat_1=46.800000000 +x_0=600000.000 +y_0=2200000.000 +units=m +no_defs <>
			</blockquote>

			The bold text makes the important difference between the EPSG and the IGNF. The IGN recommend to use the shift grid previously downloaded, and the EPSG no. As we define our GRASS location with the EPSG codes, this explains the difference we encounter between GRASS and Circé. That's the same for each projection using the NTF geodetic system.

			If you look precisely, there are also other differences between IGNF and EPSG, but they don't really have importance.


			== Define a GRASS location using the shift grid==
			We will here show how to use the IGN shift grid for a specified GRASS location. For this, we will modify the file PROJ_INFO in the folder of the mapset PERMANENT.

			If we continue with the previous projection NTF Lambert 2 étendue, which corresponds with the GRASS location NTF_L2E in my case, the file PROJ_INFO is in the folder grassdata/NTF_L2E/PERMANENT/. Open this file with a text editor. For the Linux users, add the following line at the end of the file :
			<blockquote>
			nadgrids: /usr/share/proj/ntf_r93.gsb
			</blockquote>

			For the other users, place the shift grid file in a folder of your choice. You have then to change "/usr/share/proj/" by the path of the folder you have chosen.

			To be sure your location is well defined, repeat the step of the section [[#Problem_description\|Problem description]].
			*If you have a difference lower than 1 cm, it's ok
			*Otherwise, it means the shift grid is not well taken in account. Please use the Discussion tab of this page to ask the writer of this page


			== Links ==
			[http://www.epsg-registry.org/ http://www.epsg-registry.org/]

	~~== Define~~ the ~~GRASS locations ==~~		[http://lambert93.ign.fr http://lambert93.ign.fr (fr)] : site on the new French geodetic system RGF

⚠️Thibault.lemaitre: creation of the page. Not yet ready to be published

2010-11-16T16:13:21Z

creation of the page. Not yet ready to be published

← Older revision		Revision as of 16:13, 16 November 2010
Line 1:		Line 1:
	{{ToModify}}		{{ToModify}}

	This page describes how to well use the projections defined by the ~~french~~ company IGN [http://en.wikipedia.org/wiki/Institut_G%C3%A9ographique_National (en)] [http://fr.wikipedia.org/wiki/Institut_g%C3%A9ographique_national_%28France%29 (fr)] in GRASS.		This page describes how to well use the projections defined by the French company IGN [http://en.wikipedia.org/wiki/Institut_G%C3%A9ographique_National (en)] [http://fr.wikipedia.org/wiki/Institut_g%C3%A9ographique_national_%28France%29 (fr)] in GRASS.

			In fact the French company IGN manages the projections used in France and defined them by the IGNF register. The IGN also provides a shift grid for the French geodetic systems NTF and RGF93. The French projections defined by the EPSG codes are not exactly the same than those defined by the IGN. If you use the EPSG codes instead of the IGN specifications you can encounter an error of more or less 2 m.


	~~In fact~~ the ~~french compagny IGN manages~~ the ~~projections used~~ in ~~France and defined them by~~ the ~~IGNF register~~.		== Problem description ==
			The application [http://geodesie.ign.fr/index.php?page=circe Circé] is used as a reference concerning conversions between the French projection systems. We will use it to show the problem defined in the introduction.

			#Define two GRASS locations with the EPSG code 2154 (for the projection RGF Lambert-93) and 27572 (for the projection NTF Lambert 2 étendue).
			#Open GRASS in one of these locations and define some points. Project them to the other location with GRASS.
			#Do the same conversion with Circé.
			#Compare the results obtained with GRASS and Circé : you will see an abnormal difference (between -2 and +4 meters for me).

	~~For the Linux user~~, ~~once~~ you have ~~installed GRASS, you can find~~ the ~~IGNF on your computer~~		The example was here with two particular EPSG codes, but this problem occurs each time you have to do a transformation between the geodetic systems NTF and the RGF.

	~~For~~ the ~~non Linux users~~, you can ~~open [http://lambert93~~.~~ign~~.~~fr/fileadmin/files/IGNF~~ this ~~page] and save it on~~ your ~~computer~~.		There is then 2 cases :
			*If the previous difference is negligible for your work, you can continue to use the previous defined locations as they are actually. However, don't forget that you have this error in each of your transformation.
			*If this difference is too important for your application, follow the next step to obtain a precision comparable to Circé.

			== Get the register and the grid ==
			For the Linux users, once you have installed GRASS, you can find the register and the grid on your computer. The register is named IGNF and is in the folder /usr/share/proj/. The grid is in the same folder and is named ntf_r93.gsb.

			For the non Linux users, or if you don't find the file on your computer, you can download and save [http://lambert93.ign.fr/fileadmin/files/IGNF the register] and [http://lambert93.ign.fr/fileadmin/files/ntf_r93.gsb the grid] on your computer.

			== Define the GRASS locations ==

	~~Tests :~~

	~~[http://www.example.com link title]~~

	~~[[GRASS_Community]]~~

⚠️Thibault.lemaitre: moved IGNF Register to IGNF register and shift grid NTF/RGF93: this page speaks not only of the ignf register but also of shift grid NTF/RGF93

2010-11-16T13:55:51Z

moved IGNF Register to IGNF register and shift grid NTF/RGF93: this page speaks not only of the ignf register but also of shift grid NTF/RGF93

← Older revision		Revision as of 13:55, 16 November 2010
(No difference)

← Older revision		Revision as of 11:36, 3 January 2011
Line 19:		Line 19:

	There is then 2 cases :		There is then 2 cases :
	*If the previous difference is negligible for your work, you can continue to use the previous defined locations as they are ~~actually~~. However, don't forget that you have this difference in each of your transformation.		*If the previous difference is negligible for your work, you can continue to use the previous defined locations as they are currently. However, don't forget that you have this difference in each of your transformation concerning the location NTF Lambert 2 étendue.
	*If this difference is too important for your ~~application~~, follow the next steps to obtain a precision comparable to Circé.		*If this difference is too important for your work, follow the next steps to obtain a precision comparable to Circé.


Line 26:		Line 26:
	For the Linux users, once you have installed GRASS, you can find the register and the grid on your computer. The register is named IGNF and is in the folder /usr/share/proj/. The grid is in the same folder and is named ntf_r93.gsb.		For the Linux users, once you have installed GRASS, you can find the register and the grid on your computer. The register is named IGNF and is in the folder /usr/share/proj/. The grid is in the same folder and is named ntf_r93.gsb.

	For the other users, or if you don't find the ~~file~~ on your computer, you can save [http://lambert93.ign.fr/fileadmin/files/IGNF the register] and [http://lambert93.ign.fr/fileadmin/files/ntf_r93.gsb the grid] on your computer.		For the other users, or if you don't find the files on your computer, you can save [http://lambert93.ign.fr/fileadmin/files/IGNF the register] and [http://lambert93.ign.fr/fileadmin/files/ntf_r93.gsb the grid] on your computer.


	== Differences between IGNF register and EPSG ~~code~~ ==		== Differences between IGNF register and the EPSG codes ==
	Open the IGNF register with a text editor and search for "<LAMBE>". You will then read the ~~informations about~~ the previous quoted projection NTF Lambert 2 étendue, which as the code LAMBE in the IGNF register. Below, a copy of these ~~informations~~.		Open the IGNF register with a text editor and search for "<LAMBE>". You will then read the parameters concerning the previous quoted projection NTF Lambert 2 étendue, which as the code LAMBE in the IGNF register. Below, a copy of these parameters.

	<blockquote>		<blockquote>
Line 38:		Line 38:
	The bold text makes the important difference between the EPSG and the IGNF. The IGN recommend to use the shift grid previously downloaded, and the EPSG no. As we define our GRASS location with the EPSG codes, this explains the difference we encounter between GRASS and Circé. That's the same for each projection using the NTF geodetic system.		The bold text makes the important difference between the EPSG and the IGNF. The IGN recommend to use the shift grid previously downloaded, and the EPSG no. As we define our GRASS location with the EPSG codes, this explains the difference we encounter between GRASS and Circé. That's the same for each projection using the NTF geodetic system.

	If you look precisely, there are also other differences between IGNF and EPSG, but they ~~don't really~~ have importance.		If you look precisely, there are also other differences between IGNF and EPSG, but they have lesser importance.


	== Define a GRASS location using the shift grid==		== Define a GRASS location using the shift grid ==
	We will here show how to use the IGN shift grid for a specified GRASS location. For this, we will put the grid in a place where GRASS can use it and modify the file PROJ_INFO ~~in the folder~~ of the ~~mapset PERMANENT~~.		We will here show how to use the IGN shift grid for a specified GRASS location. For this, we will put the grid in a place where GRASS can use it and modify the file PROJ_INFO of the concerned location.

	First, you have to ~~place~~ the grid in the folder etc/nad/ of GRASS. For example, with the version 6.4 on Linux, the concerned folder is /usr/lib/grass64/etc/nad/. You can also create a link instead of a copy with this command :		First, you have to copy the grid in the folder etc/nad/ of GRASS. For example, with the version 6.4 on Linux, the concerned folder is /usr/lib/grass64/etc/nad/. You can also create a link instead of a copy with this command :
	<blockquote>		<blockquote>
	gksudo ln -s /usr/share/proj/ntf_r93.gsb /usr/lib/grass64/etc/nad/ntf_r93.gsb		gksudo ln -s /usr/share/proj/ntf_r93.gsb /usr/lib/grass64/etc/nad/ntf_r93.gsb
	</blockquote>		</blockquote>
	Note that you must have the administrator rights to do this on Linux		Note that you must have the administrator rights to do this on Linux.
	For the Windows users you don't need to be an administrator and the folder is something like C://Program Files/grass64/etc/nad/.		For the Windows users you don't need to be an administrator and the folder is something like C://Program Files/grass64/etc/nad/.

	If we continue with the previous projection NTF Lambert 2 étendue, which corresponds with the GRASS location NTF_L2E in my case, the file PROJ_INFO is in the folder grassdata/NTF_L2E/PERMANENT/. Open this file with a text editor. ~~For the Linux users, add~~ the following line at the end of ~~the~~ file :		If we continue with the previous projection NTF Lambert 2 étendue, which corresponds with the GRASS location NTF_L2E in my case, the file PROJ_INFO is in the folder grassdata/NTF_L2E/PERMANENT/. Open this file with a text editor. Add the following line at the end of this file :
	<blockquote>		<blockquote>
	nadgrids: ntf_r93.gsb		nadgrids: ntf_r93.gsb