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.. _topocentric:
================================================================================
Geocentric to topocentric conversion
================================================================================
.. versionadded:: 8.0.0
Convert geocentric coordinates to topocentric coordinates (in the forward path).
+---------------------+--------------------------------------------------------+
| **Alias** | topocentric |
+---------------------+--------------------------------------------------------+
| **Domain** | 3D |
+---------------------+--------------------------------------------------------+
| **Input type** | Geocentric cartesian coordinates |
+---------------------+--------------------------------------------------------+
| **Output type** | Topocentric cartesian coordinates |
+---------------------+--------------------------------------------------------+
This operation converts geocentric coordinate values (X, Y, Z) to topocentric
(E/East, N/North, U/Up) values. This is also sometimes known as the ECEF (Earth
Centered Earth Fixed) to ENU conversion.
Topocentric coordinates are expressed in a frame whose East and North axis form
a local tangent plane to the Earth's ellipsoidal surface fixed to a specific
location (the topocentric origin), and the Up axis points upwards along the
normal to that plane.
.. image:: ./images/ECEF_ENU_Longitude_Latitude_relationships.png
:align: center
:scale: 100%
:alt: ENU coordinate frame
..
Source : https://en.wikipedia.org/wiki/Local_tangent_plane_coordinates#/media/File:ECEF_ENU_Longitude_Latitude_relationships.svg
Public domain
..
The topocentric origin is a required parameter of the conversion, and can be
expressed either as geocentric coordinates (``X_0``, ``Y_0`` and ``Z_0``) or
as geographic coordinates (``lat_0``, ``lon_0``, ``h_0``).
When conversion between geographic and topocentric coordinates is desired, the
topocentric conversion must be preceded by the :ref:`cart` conversion to
perform the initial geographic to geocentric coordinates conversion.
The formulas used come from the "Geocentric/topocentric conversions" paragraph
of :cite:`IOGP2018`. ``+proj=topocentric`` alone corresponds to the ``EPSG:9836``
conversion method, ``+proj=cart`` followed by ``+proj=topocentric`` corresponds
to ``EPSG:9837``.
Usage
################################################################################
Convert geocentric coordinates to topocentric coordinates, with the topocentric
origin specified in geocentric coordinates::
echo 3771793.968 140253.342 5124304.349 2020 | \
cct -d 3 +proj=topocentric +ellps=WGS84 +X_0=3652755.3058 +Y_0=319574.6799 +Z_0=5201547.3536
-189013.869 -128642.040 -4220.171 2020.0000
Convert geographic coordinates to topocentric coordinates, with the topocentric
origin specified in geographic coordinates::
echo 2.12955 53.80939444 73 2020 | cct -d 3 +proj=pipeline \
+step +proj=cart +ellps=WGS84 \
+step +proj=topocentric +ellps=WGS84 +lon_0=5 +lat_0=55 +h_0=200
-189013.869 -128642.040 -4220.171 2020.0000
Parameters
################################################################################
.. include:: ../options/ellps.rst
Topocentric origin described as geocentric coordinates
------------------------------------------------------
.. note::
The below options are mutually exclusive with the ones to express the origin as geographic coordinates.
.. option:: +X_0=<value>
Geocentric X value of the topocentric origin (in metre)
.. option:: +Y_0=<value>
Geocentric Y value of the topocentric origin (in metre)
.. option:: +Z_0=<value>
Geocentric Z value of the topocentric origin (in metre)
Topocentric origin described as geographic coordinates
------------------------------------------------------
.. note::
The below options are mutually exclusive with the ones to express the origin as geocentric coordinates.
.. option:: +lat_0=<value>
Latitude of topocentric origin (in degree)
.. option:: +lon_0=<value>
Longitude of topocentric origin (in degree)
.. option:: +h_0=<value>
Ellipsoidal height of topocentric origin (in metre)
*Defaults to 0.0.*
|
