Записки программиста, обо всем и ни о чем. Но, наверное, больше профессионального.

2009-10-24

38 попугаев

Вот засада: карта трубопровода в географических координатах (Geodetic Coordinates), ну там Latitude, Longitude. Градусы. А длина труб нужна в метрах.
Крутой геософт вроде как считает длины и автоматом заполняет колонку в БД, именованную "длина", но, бяка такая, как и положено роботу, заполняет по тупому - в градусах. Длина труб в градусах. Фигня какая.

Хорошо, что БД лежит в Оракле. У Оракла есть документация и в ней написано: используйте метод

SDO_GEOM.SDO_LENGTH(
geom IN SDO_GEOMETRY,
tol IN NUMBER
[, unit IN VARCHAR2]
) RETURN NUMBER;

если вам длину надо. А необязательным параметром "юнит" укажите единицы измерения.
Обожаю СУБД ораклевую.
Интересно, в постгре также легко задачки решаются?

В итоге, чтобы найти длину отрезка трубы в метрах, я пишу сиквельный запрос:

select hm.arcnum, SDO_GEOM.SDO_LENGTH(hm.geom, 0.00001, 'unit=M') ln
from tgk.heatmain hm
where hm.arcnum=3;

И получаю в колонке 'ln' то, что надо.

6.1.1 Coordinate System (Spatial Reference System)

A coordinate system (also called a spatial reference system) is a means of assigning coordinates to a location and establishing relationships between sets of such coordinates. It enables the interpretation of a set of coordinates as a representation of a position in a real world space.

The term coordinate reference system has the same meaning as coordinate system for Spatial, and the terms are used interchangeably. European Petroleum Survey Group (EPSG) specifications and documentation typically use the term coordinate reference system. (EPSG has its own meaning for the term coordinate system, as noted in Section 6.6.11.)
6.1.2 Cartesian Coordinates

Cartesian coordinates are coordinates that measure the position of a point from a defined origin along axes that are perpendicular in the represented two-dimensional or three-dimensional space.
6.1.3 Geodetic Coordinates (Geographic Coordinates)

Geodetic coordinates (sometimes called geographic coordinates) are angular coordinates (longitude and latitude), closely related to spherical polar coordinates, and are defined relative to a particular Earth geodetic datum (described in Section 6.1.6). For more information about geodetic coordinate support, see Section 6.2.
6.1.4 Projected Coordinates

Projected coordinates are planar Cartesian coordinates that result from performing a mathematical mapping from a point on the Earth's surface to a plane. There are many such mathematical mappings, each used for a particular purpose.
6.1.5 Local Coordinates

Local coordinates are Cartesian coordinates in a non-Earth (non-georeferenced) coordinate system. Section 6.3 describes local coordinate support in Spatial.
6.1.6 Geodetic Datum

A geodetic datum (or datum) is a means of shifting and rotating an ellipsoid to represent the figure of the Earth, usually as an oblate spheroid, that approximates the surface of the Earth locally or globally, and is the reference for the system of geodetic coordinates.

Each geodetic coordinate system is based on a datum.
6.1.7 Transformation

Transformation is the conversion of coordinates from one coordinate system to another coordinate system.

If the coordinate system is georeferenced, transformation can involve datum transformation: the conversion of geodetic coordinates from one geodetic datum to another geodetic datum, usually involving changes in the shape, orientation, and center position of the reference ellipsoid.


oracle.com/docs/.../sdo_cs_concepts


Сцылки дня:
Собрание сочинений Алексея Федорчука, популизатора линукса.

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