OGC标准学习手记（一）：OGC标准概述
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OGC（http://www.opengeospatial.org/）是The Open Geospatial Consortium, Inc.（开放空间信息协会）的简称。它组织各成员单位制定了一系列地理信息共享方面的标准，包括SLD、WSC、WCS、GML、WMS和WFS等。
Catalogue Services
： The OpenGIS Catalogue Services Specification defines common interfaces to discover, browse, and query metadata about data, services, and other potential resources.
Coordinate Transformation Service ：Implementation Specification provides interfaces for general positioning, coordinate systems, and coordinate transformations. "
Filter Encoding：The OpenGIS® Filter Encoding Implementation Specification defines an XML encoding for filter expressions. A filter expression constrains property values to create a subset of a group of objects. The goal, typically, is to operate on just those objects by, for example, rendering them in a different color or saving them to another format.
Geographic Objects：The OpenGIS® Geographic Objects (GO) Implementation Specification defines an open set of common, lightweight, language-independent abstractions for describing, managing, rendering, and manipulating geometric and geographic objects within an application programming environment.
GML in JPEG 2000 for Geographic Imagery Encoding
Grid Coverage Service：The OpenGIS® Grid Coverage Service Implementation Specification defines methods that allow interoperability between software implementations by data vendors and software vendors providing grid (raster) analysis and processing capabilities.
Sensor Model Language (SensorML)：The primary focus of SensorML is to define processes and processing components associated with the measurement and post-measurement transformation of observations. The SensorML document also defines the SWE Common data types used throughout the SWE encodings and services.
Sensor Planning Service (SPS)：Sensor Planning Service (SPS) defines an interface to task any form of sensor or model. Using SPS, sensors can be reprogrammed or calibrated, sensor missions can be started or changed, simulation models executed and controlled. The feasibility of a tasking request can be checked and alternatives may be provided. SPS implementations cover a wide range of application scenarios. SPS is currently used to control assets such as simple web cams as well as satellite missions.
Simple Feature Access - Part 1: Common Architecture
Simple Feature Access - Part 2: SQL Option
Simple Features for CORBA：The three OpenGIS® Simple Features Implementation Specifications (one each for OLE/COM, CORBA, and SQL) define interfaces that enable transparent access to geographic data held in heterogeneous processing systems on distributed computing platforms.The Simple Feature Specification application programming interfaces (APIs) provide for publishing, storage, access, and simple operations on Simple Features (point, line, polygon, multi-point, etc). The purpose of these specifications is to describe interfaces to allow GIS software engineers to develop applications that expose functionality required to access and manipulate geospatial information comprising features with 'simple' geometry using different technologies.
Styled Layer Descriptor：This document explains how the Web Map Server specification can be extended to allow user-defined symbolization of feature and coverage data. It should be read in conjunction with the latest version WMS specification. At the time of writing the latest version WMS specification was defined by the WMS 1.3 Specification.This document is together with the Symbology Encoding Implementation Specification the direct follow-up of Styled Layer Descriptor Implementation Specification
Symbology Encoding：This Specification defines Symbology Encoding, an XML language for styling information that can be applied to digital Feature and Coverage data.
This document is together with the Styled Layer Descriptor Profile for the Web Map Service Implementation Specification the direct follow-up of Styled Layer Descriptor Implementation Specification
Transducer Markup Language (TML)：TML defines:
* a set of models describing the response characteristics of a transducer
* an efficient method for transporting sensor data and preparing it for fusion through spatial and temporal associations
Web Feature Service (WFS)：The OpenGIS® Web Feature Service (WFS) Implementation Specification allows a client to retrieve and update geospatial data encoded in Geography Markup Language (GML) from multiple Web Feature Services. The specification defines interfaces for data access and manipulation operations on geographic features, using HTTP as the distributed computing platform. Via these interfaces, a Web user or service can combine, use and manage geodata -- the feature information behind a map image -- from different sources.
The following WFS operations are available to manage and query geographic features and elements:
* Create a new feature instance
* Delete a feature instance
* Update a feature instance
* Lock a feature instance
* Get or query features based on spatial and non-spatial constraints
Web Map Context (WMC)：The OpenGIS® Web Map Context (WMC) Implementation Specification is a companion to the OpenGIS® Web Map Service. It describes how to save a map view comprised of many different layers from different Web Map Servers. A 'context' can be encoded and saved so that Web maps created by users can be automatically reconstructed and augmented by the authoring user or other users in the future.
Web Map Service (WMS)：The OpenGIS® Web Map Service (WMS) Implementation Specification provides three operations (GetCapabilities, GetMap, and GetFeatureInfo) in support of the creation and display of registered and superimposed map-like views of information that come simultaneously from multiple remote and heterogeneous sources.
其中比较重要的现在用得比较多的标准是GML、WMS和WFS。
GML是一个基于XML之上的地理信息描述、转换、传输标准。它有两个主要用途。
（1） 地理数据的转换。它可以作为一个公共的地理空间数据转换格式标准，不同软件生产的数据可以转换到这一用XML描述，按照ISO 19117空间模型表达的数据格式，应用软件可以读取这一格式转到相应的系统中。
（2） 地理数据实时传输协议。当两个系统要进行在线互操作时，按照这种公共描述语言描述的格式进行实时通讯，可以实现互操作。
WMS全称是“Web Map Service”（网络地图服务）。此标准主要定义了用于创建和显示地图图像的三大操作：GetCapabilities（获取服务能力）, GetMap（获取地图）和GetFeatureInfo（获取对象信息）。其中GetMap为核心操作，此操作得到一幅地图图像。
WFS是一个基于Web服务技术的地理要素在线服务标准，它有两方面的作用。一是实现地理数据的Web服务[5]。数据服务部门建立了地理空间数据库的系统，对外提供在线服务，用户可以通过该标准得到自己所需要的地理空间数据。二是用于异构系统互操作规范。两个不同的地理信息系统可以实现异构数据互操作，包括数据查询、浏览、提取、修改、更新等操作。它基于Web技术可以实现远程互操作。
WFS的功能包括5个操作：
（1） GetCapabilities （获取服务能力）
（2） DescribeFeatureType （要素类型特征描述）
（3） GetFeature （获取对象）
（4） Transaction （事务处理包括增、删、修改要素）
（5） LockFeature （锁要素）
其中前三个操作为必须实现的操作，它可以获取地理要素；后两个为可选操作，它主要用于增、删、修改地理要素。
另外，还需注意标准文档的类型（Type），一般下载IS类型文本即可。其中，据我的理解：
D-RP（Deprecated Recommendation Paper）可翻译成：没有被采纳的建议稿
IS（Implementation Specification）可翻译成：执行规范，这是当前采用的规范稿
DP（Discussion Paper）可翻译成：讨论稿
D-IS（Deprecated Implementation Specification）可翻译成：已废除的执行规范