Changes between Initial Version and Version 1 of rfc61_support_for_measured_geometries

Timestamp:

Jan 27, 2016, 12:27:18 PM (8 years ago)

Author:

Ari Jolma

Comment:

Restart page from rfc61

rfc61_support_for_measured_geometries

@@ +1 @@
+= RFC 61 : Support for measured geometries =
+
+Author: Ari Jolma[[BR]]
+
+Contact: ari.jolma at gmail.com[[BR]]
+
+Status: Draft[[BR]]
+
+Implementation version: 2.1 or 2.2
+
+== Summary ==
+
+This RFC defines how to implement measured geometries (geometries, where the points have M coordinate, i.e., they are XYM or XYZM).
+
+== Rationale ==
+
+M coordinate is in the OGC simple feature model and it is used in many vector data formats.
+
+== Changes ==
+
+Changes are required into the C++ API and the C API needs to be enhanced. Several drivers need to be changed to take advantage of this enhancement but also due to the changes in the C++ API.
+
+=== Common API ===
+
+ogr_core.h:
+{{{
+#define OGR_G_NOT_EMPTY 1
+#define OGR_G_3D 3
+#define OGR_G_MEASURED 5
+}}}
+
+New OGRwkbGeometryType values are needed - that is rather complex system now due to history.
+
+=== C++ API ===
+
+Change int nCoordDimension to int flags, which is used to keep track of whether the geometry is empty (currently hacks such as nCoordDimension == -2 is used for that), has Z, or is measured. IsEmpty = flags & ~OGR_G_NOT_EMPTY, Is3D = flags & OGR_G_3D, IsMeasured = flags & OGR_G_MEASURED.
+
+Keep, but deprecate 
+{{{
+getCoordinateDimension();
+setCoordinateDimension();
+}}}
+
+class OGRGeometry:
+{{{
+//Add methods:
+int CoordinateDimension();
+OGRBoolean Is3D();
+OGRBoolean IsMeasured();
+virtual void set3D(OGRBoolean bIs3D);
+virtual void setMeasured(OGRBoolean bIsMeasured);
+
+//Add now or later methods:
+virtual OGRGeometry *LocateAlong(double mValue);
+virtual OGRGeometry *LocateBetween(double mStart, double mEnd);
+}}}
+
+Add property double m to class OGRPoint. Add constructor, getters, and setters for it.
+
+Add property double *padfM to class OGRSimpleCurce. Add constructor, getters, and setters for it. The getters and setters can take advantage of the flags to determine whether Z or M is to be set in some of them. For backwards compatibility Z is preferred.
+
+Override methods set3D and setMeasured in those classes where setCoordinateDimension is overridden.
+
+=== C API ===
+
+ogr_core.h:
+{{{
+OGRwkbGeometryType CPL_DLL OGR_GT_SetM( OGRwkbGeometryType eType );
+int                CPL_DLL OGR_GT_HasM( OGRwkbGeometryType eType );
+}}}
+ogr_api.h: (new versions of some functions are needed, use postfix M)
+{{{
+void   CPL_DLL OGR_G_Is3D( OGRGeometryH );
+void   CPL_DLL OGR_G_IsMeasured( OGRGeometryH );
+
+void   CPL_DLL OGR_G_Set3D( OGRGeometryH, int );
+void   CPL_DLL OGR_G_SetMeasured( OGRGeometryH, int );
+
+int    CPL_DLL OGR_G_GetPointsM( OGRGeometryH hGeom,
+                                 void* pabyX, int nXStride,
+                                 void* pabyY, int nYStride,
+                                 void* pabyZ, int nZStride,
+                                 void* pabyM, int nMStride);
+double CPL_DLL OGR_G_GetM( OGRGeometryH, int );
+void   CPL_DLL OGR_G_GetPointM( OGRGeometryH, int iPoint, 
+                                double *, double *, double *, double * );
+void   CPL_DLL OGR_G_SetPointM( OGRGeometryH, int iPoint, 
+                                double, double, double, double );
+void   CPL_DLL OGR_G_AddPointM( OGRGeometryH, double, double, double, double );
+void   CPL_DLL OGR_G_SetPointsM( OGRGeometryH hGeom, int nPointsIn,
+                                 void* pabyX, int nXStride,
+                                 void* pabyY, int nYStride,
+                                 void* pabyZ, int nZStride,
+                                 void* pabyM, int nMStride );
+
+}}}
+
+ogr_p.g
+{{{
+const char CPL_DLL * OGRWktReadPointsM( const char * pszInput,
+                                       OGRRawPoint **ppaoPoints, 
+                                       double **ppadfZ,
+                                        double **ppadfM,
+                                       int * pnMaxPoints,
+                                       int * pnReadPoints );
+void CPL_DLL OGRMakeWktCoordinateM( char *, double, double, double, double, int );
+
+}}}
+
+pggeometry.h is internal, so we can change the function prototype
+{{{
+void OGRCreateFromMultiPatchPart(OGRMultiPolygon *poMP,
+                                 OGRPolygon*& poLastPoly,
+                                 int nPartType,
+                                 int nPartPoints,
+                                 double* padfX,
+                                 double* padfY,
+                                 double* padfZ,
+                                 double* padfM);
+}}}
+
+
+== SWIG bindings (Python / Java / C# / Perl) changes ==
+
+The new C API functions need to be exposed through swig. Further changes depend on whether the language bindings are aware of coordinates. At least Python and Perl are.
+
+== Drivers ==
+
+Drivers that are probably affected by the C++ changes are at least (these use the CoordinateDimension API) pg, mssqlspatial, sqlite, db2, mysql, gml, pgdump, geojson, libkml, gpkg, wasp, gpx, filegdb, vfk, bna, dxf.
+
+
+== Utilities ==
+
+to do
+
+== Documentation ==
+
+All new methods/functions are documented.
+
+== Test Suite ==
+
+to do
+
+== Compatibility Issues ==
+
+to do
+
+== Related tickets ==
+
+https://trac.osgeo.org/gdal/ticket/6063
+https://trac.osgeo.org/gdal/ticket/6331
+
+== Implementation ==
+
+The implementation will be done by Ari Jolma.
+
+The proposed implementation will be in https://github.com/ajolma/GDAL-XYZM
+
+== Voting history