HotineObliqueMercatorProjection.TrueOrigin Property
Gets a property telling where the true origin is located.
Syntax
public HotineObliqueMercatorTrueOrigin TrueOrigin { get; }Property Value
Default: HotineNaturalOriginNearEquator
One of the HotineObliqueMercatorTrueOrigin values.
Remarks
The so-called true origin of a map projection is the point whose projected coordinates are (FalseEasting, FalseNorthing). For most projections types, there is no disagreement about how the true origin should be defined, but for the HotineObliqueMercatorProjection, there are two alternatives:
HotineNaturalOriginNearEquator. The true origin is the nearest intersection of the central line and the so-called aposphere equator (which is an auxiliary line near the ordinary equator). This intersection, called the natural origin by EPSG, was used as true origin for two projections for West and East Malaysia by Martin Hotine. Many other instances of the projection are expressed in the same way.
CentralPoint. The true origin is the central point, whose geographic coordinates are (CentralLongitude, CentralLatitude). This alternative resembles how most other projections work, and may be the best alternative if one would develop a new instance of the projection.
A projection instance, expressed using one alternative, can always be expressed using the other alternative as well, since the FalseEasting and FalseNorthing can be adjusted to compensate.
The table shows how the two alternatives are expressed in other systems.
Carmenta Engine | PROJ | EPSG before 2010 | EPSG since 2010 | GDAL/OGR WKT | ESRI WKT |
|---|---|---|---|---|---|
HotineObliqueMercatorProjection, trueOrigin = HotineNaturalOriginNearEquator | +proj=omerc +no_uoff | Hotine Oblique Mercator | Hotine Oblique Mercator, Variant A | Hotine_Oblique_Mercator | Hotine_Oblique_Mercator_Azimuth_Natural_Origin |
HotineObliqueMercatorProjection, trueOrigin = CentralPoint | +proj=omerc | Oblique Mercator | Hotine Oblique Mercator, Variant B | Hotine_Oblique_Mercator_Azimuth_Center | Hotine_Oblique_Mercator_Azimuth_Center |
The ESRI column is incomplete, since they would use Rectified_Skew_Orthomorphic_Natural_Origin (for the first row) if the Azimuth differs from the RectifiedGridAngle. (ESRI also supports Hotine_Oblique_Mercator_Two_Point_Natural_Origin and Hotine_Oblique_Mercator_Two_Point_Center, where the central line is specified by two points instead of a point and an azimuth. The two-point construction is also supported by PROJ, but not by Carmenta or EPSG.)
Platforms
Windows, Linux, Android