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<p>Le 2023-10-18 à 20 h 46, Javier Jimenez Shaw via PROJ a écrit :</p>
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cite="mid:CADRrdKvg+eq8WjbXOUFS9BwxkrKzH=shpfaLK3ic5TT=7=NLGQ@mail.gmail.com">
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<p>Do you mean that a geocentric system is using the geodetic
latitude and the geodetic system is using a geocentric
latitude? Interesting</p>
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<p>No. There is no explicit <font face="monospace">GeocentricCRS</font>
type in ISO 19111. The addition of a <font face="monospace">GeocentricCRS</font>
type has been debated during OGC meetings and excluded for reasons
that I do not fully understood, but my remembrance is that it was
indeed related to semantic issues. There is an explicit <font
face="monospace">GeocentricCRS</font> type in GeoAPI, but it is
inherited from OGC 01-009 (a specification that predates ISO
19111), and PROJ 5 took inspiration from that as well.<br>
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<p>In ISO 19111, <font face="monospace">GeodeticCRS</font> is a
base type which can have either geodetic or geocentric latitude,
depending on their coordinate system:</p>
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<li><font face="monospace">GeodeticCRS</font> associated to <font
face="monospace">SphericaCS</font> use geocentric latitudes.
ISO 19111 rather call that "spherical latitudes".</li>
<li><font face="monospace">GeodeticCRS</font> associated to <font
face="monospace">EllipsoidalCS</font> use geodetic latitudes.</li>
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<p><font face="monospace">GeographicCRS</font> is a specialization
of <font face="monospace">GeodeticCRS</font> restricted to case 2
above. As said above, the introduction of a <font
face="monospace">GeocentricCRS</font> as a specialization of <font
face="monospace">GeodeticCRS</font> for case 1 has been debated
but rejected at OGC, so for now we have to use the generic <font
face="monospace">GeodeticCRS</font> base class. However it does
not mean that ISO 19111 will not revisit this issue in some future
version.</p>
<p> Martin</p>
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