vcl-dxmapcontrolprojections.md
The base class for map projections.
TdxMapControlCustomProjection = class(
TcxInterfacedPersistent
)
Map projections are different ways to map a sphere surface to a plane. However, each map projection distorts the original surface. For example, surface distortion increases as the inspected point moves away from the equator towards the north or south pole in the Spherical Mercator projection. Different map projection types are designed for use in different scenarios.
Refer to the following topic for general information on map projections: https://en.wikipedia.org/wiki/Map_projection.
The TdxMapControlCustomProjection class declares geographic conversion functions common to all map projections. TdxMapControlCustomProjection descendants implement these functions.
All map layer types support the Spherical Mercator projection ( default ). Item and Item File layers declare Projection and ProjectionClass properties you can use to switch between the following projections:
| Projection | Example |
|---|---|
| Braun Stereographic | |
| Elliptical Mercator | |
| EPSG:4326 (also known as WGS 84 or WGS 1984) | |
| Equal-Area | |
| Equirectangular | |
| Kavrayskiy VII | |
| Lambert Cylindrical Equal-Area | |
| Miller Cylindrical | |
| Sinusoidal | |
| Spherical Mercator |
The list below outlines key members of the TdxMapControlCustomProjection class. These members allow you to convert map points into specific measurement units according to the actual map projection.
GeoPointToMapUnitConverts a specified point defined in geographical coordinates to internal map units.GeoToKilometersSizeThis member supports the internal infrastructure and is not intended to be used directly from your code.KilometersToGeoSizeThis member supports the internal infrastructure and is not intended to be used directly from your code.MapUnitToGeoPointConverts a specified point defined in internal map units to geographical coordinates.
Do not use the TdxMapControlCustomProjection class directly. Use the following descendants instead:
TdxMapControlBraunStereographicProjectionImplements the Braun Stereographic map projection.TdxMapControlEllipticalMercatorProjectionImplements the Elliptical Mercator Projection.TdxMapControlEPSG4326ProjectionImplements the EPSG:4326 map projection (also known as WGS 84 or WGS 1984).TdxMapControlEqualAreaProjectionImplements the Equal-Area map projection.TdxMapControlEquirectangularProjectionImplements the Equirectangular map projection.TdxMapControlKavrayskiyProjectionImplements the Kavrayskiy VII map projection.TdxMapControlLambertCylindricalEqualAreaProjectionImplements the Lambert Cylindrical Equal-Area map projection.TdxMapControlMillerProjectionImplements the Miller map projection.TdxMapControlSinusoidalProjectionImplements the Sinusoidal map projection.TdxMapControlSphericalMercatorProjectionImplements the Spherical Mercator map projection.
TObject TPersistent TInterfacedPersistent TcxInterfacedPersistent TdxMapControlCustomProjection
See Also
dxMapControlProjections.dxRegisteredMapProjections