When upgrading an old database with french IGN

doc/installation.xml

@@ -2483,6 +2483,34 @@ ALTER EXTENSION postgis_topology UPDATE TO "&last_release_version;next";</progra
 		<programlisting>ALTER TABLE spatial_ref_sys ADD CONSTRAINT spatial_ref_sys_srid_check check (srid &gt; 0 AND srid &lt; 999000 );</programlisting>
 
 		<programlisting>ALTER TABLE spatial_ref_sys ADD PRIMARY KEY(srid));</programlisting>
+
+		If you are upgrading an old database containing french <ulink url="https://en.wikipedia.org/wiki/Institut_g%C3%A9ographique_national">
+			IGN
+		  </ulink> cartography, you will have probably SRIDs out 
+		of range and you will see, when importing your database, issues like this :
+
+		<programlisting> WARNING: SRID 310642222 converted to 999175 (in reserved zone)</programlisting>
+
+		In this case, you can try following steps : first throw 
+		out completely the IGN from the sql which is resulting 
+		from postgis_restore.pl. So, after having run :
+
+		<programlisting>perl utils/postgis_restore.pl "/somepath/olddb.backup" > oldbb.sql</programlisting>
+
+		run this command :
+
+		<programlisting>grep -v IGNF olddb.sql > olddb-without-IGN.sql</programlisting>
+
+		Create then your newdb, activate the required Postgis extensions, 
+		and insert properly the french system IGN with :
+
+		<ulink url="https://raw.githubusercontent.com/Remi-C/IGN_spatial_ref_for_PostGIS/master/Put_IGN_SRS_into_Postgis.sql">
+			this script
+		  </ulink>
+
+		After these operations, import your data :
+
+		<programlisting>psql -h localhost -p 5432 -U postgres -d newdb -f olddb-without-IGN.sql  2> errors.txt</programlisting>
 
 	</para>
 	</listitem>