Merge pull request #1722 from rouault/document_identify_oddity

Doc: document oddity related to identification of CRS from ESRI WKT

2 files changed, 58 insertions, 21 deletions

diff --git a/src/iso19111/c_api.cpp b/src/iso19111/c_api.cpp
index f3badb51..5f34a22b 100644
--- a/src/iso19111/c_api.cpp
+++ b/src/iso19111/c_api.cpp
@@ -2158,14 +2158,26 @@ PJ *proj_get_target_crs(PJ_CONTEXT *ctx, const PJ *obj) {
  * The method returns a list of matching reference CRS, and the percentage
  * (0-100) of confidence in the match. The list is sorted by decreasing
  * confidence.
- *
- * 100% means that the name of the reference entry
+ * <ul>
+ * <li>100% means that the name of the reference entry
  * perfectly matches the CRS name, and both are equivalent. In which case a
  * single result is returned.
- * 90% means that CRS are equivalent, but the names are not exactly the same.
- * 70% means that CRS are equivalent), but the names do not match at all.
- * 25% means that the CRS are not equivalent, but there is some similarity in
- * the names.
+ * Note: in the case of a GeographicCRS whose axis
+ * order is implicit in the input definition (for example ESRI WKT), then axis
+ * order is ignored for the purpose of identification. That is the CRS built
+ * from
+ * GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.257223563]],
+ * PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]]
+ * will be identified to EPSG:4326, but will not pass a
+ * isEquivalentTo(EPSG_4326, util::IComparable::Criterion::EQUIVALENT) test,
+ * but rather isEquivalentTo(EPSG_4326,
+ * util::IComparable::Criterion::EQUIVALENT_EXCEPT_AXIS_ORDER_GEOGCRS)
+ * </li>
+ * <li>90% means that CRS are equivalent, but the names are not exactly the same.</li>
+ * <li>70% means that CRS are equivalent), but the names do not match at all.</li>
+ * <li>25% means that the CRS are not equivalent, but there is some similarity in
+ * the names.</li>
+ * </ul>
  * Other confidence values may be returned by some specialized implementations.
  *
  * This is implemented for GeodeticCRS, ProjectedCRS, VerticalCRS and
diff --git a/src/iso19111/crs.cpp b/src/iso19111/crs.cpp
index b9b38c80..2cae3851 100644
--- a/src/iso19111/crs.cpp
+++ b/src/iso19111/crs.cpp
@@ -697,14 +697,26 @@ CRSNNPtr CRS::normalizeForVisualization() const {
  * The method returns a list of matching reference CRS, and the percentage
  * (0-100) of confidence in the match. The list is sorted by decreasing
  * confidence.
- *
- * 100% means that the name of the reference entry
+ * <ul>
+ * <li>100% means that the name of the reference entry
  * perfectly matches the CRS name, and both are equivalent. In which case a
  * single result is returned.
- * 90% means that CRS are equivalent, but the names are not exactly the same.
- * 70% means that CRS are equivalent), but the names do not match at all.
- * 25% means that the CRS are not equivalent, but there is some similarity in
- * the names.
+ * Note: in the case of a GeographicCRS whose axis
+ * order is implicit in the input definition (for example ESRI WKT), then axis
+ * order is ignored for the purpose of identification. That is the CRS built
+ * from
+ * GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.257223563]],
+ * PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]]
+ * will be identified to EPSG:4326, but will not pass a
+ * isEquivalentTo(EPSG_4326, util::IComparable::Criterion::EQUIVALENT) test,
+ * but rather isEquivalentTo(EPSG_4326,
+ * util::IComparable::Criterion::EQUIVALENT_EXCEPT_AXIS_ORDER_GEOGCRS)
+ * </li>
+ * <li>90% means that CRS are equivalent, but the names are not exactly the same.</li>
+ * <li>70% means that CRS are equivalent), but the names do not match at all.</li>
+ * <li>25% means that the CRS are not equivalent, but there is some similarity in
+ * the names.</li>
+ * </ul>
  * Other confidence values may be returned by some specialized implementations.
  *
  * This is implemented for GeodeticCRS, ProjectedCRS, VerticalCRS and
@@ -1596,17 +1608,30 @@ static bool hasCodeCompatibleOfAuthorityFactory(
  * authorityFactory is not null.
  *
  * The method returns a list of matching reference CRS, and the percentage
- * (0-100) of confidence in the match.
- * 100% means that the name of the reference entry
+ * (0-100) of confidence in the match:
+ * <ul>
+ * <li>100% means that the name of the reference entry
  * perfectly matches the CRS name, and both are equivalent. In which case a
  * single result is returned.
- * 90% means that CRS are equivalent, but the names are not exactly the same.
- * 70% means that CRS are equivalent (equivalent datum and coordinate system),
- * but the names do not match at all.
- * 60% means that ellipsoid, prime meridian and coordinate systems are
- * equivalent, but the CRS and datum names do not match.
- * 25% means that the CRS are not equivalent, but there is some similarity in
- * the names.
+ * Note: in the case of a GeographicCRS whose axis
+ * order is implicit in the input definition (for example ESRI WKT), then axis
+ * order is ignored for the purpose of identification. That is the CRS built
+ * from
+ * GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.257223563]],
+ * PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]]
+ * will be identified to EPSG:4326, but will not pass a
+ * isEquivalentTo(EPSG_4326, util::IComparable::Criterion::EQUIVALENT) test,
+ * but rather isEquivalentTo(EPSG_4326,
+ * util::IComparable::Criterion::EQUIVALENT_EXCEPT_AXIS_ORDER_GEOGCRS)
+ * </li>
+ * <li>90% means that CRS are equivalent, but the names are not exactly the same.
+ * <li>70% means that CRS are equivalent (equivalent datum and coordinate system),
+ * but the names do not match at all.</li>
+ * <li>60% means that ellipsoid, prime meridian and coordinate systems are
+ * equivalent, but the CRS and datum names do not match.</li>
+ * <li>25% means that the CRS are not equivalent, but there is some similarity in
+ * the names.</li>
+ * </ul>
  *
  * @param authorityFactory Authority factory (or null, but degraded
  * functionality)