osgEarth 2.10 官方文档：地理空间SDK与地形引擎

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"osgEarth Documentation - Release 2.10" osgEarth是一个针对OpenSceneGraph应用程序的地理空间SDK和地形引擎。这个项目的目标是： 1. 支持在OpenSceneGraph基础上开发3D地理空间应用。 2. 使直接从源数据可视化地形模型和图像变得尽可能简单。 3. 与开放地图标准、技术和数据进行互操作。如果你正在寻找一个工具来简化3D地理空间应用的开发，并且需要处理地形数据和图像的可视化，osgEarth可能就是你需要的。它消除了创建离线地形数据库的需求，而是直接处理原始数据，这使得地理数据的处理更为高效和便捷。文档包含以下章节： 1. 关于项目：介绍osgEarth的基本概念和目标。 2. 构建osgEarth：这部分指导用户如何构建和安装osgEarth，这对于开发者来说至关重要。 3. 用户指南：提供给用户使用osgEarth的基本步骤和教程，帮助他们快速上手。 4. 开发者话题：面向程序员，详细解释了如何扩展和自定义osgEarth的功能。 5. 处理数据：这部分介绍了如何加载和操作各种地理数据，包括地形和影像数据。 6. 参考指南：提供了详细的API和其他技术参考信息，供开发者深入研究。 7. 常见问题（FAQ）：解答了用户在使用osgEarth过程中可能遇到的问题。 8. 发行说明：列出了版本2.10的主要更新和改进。 9. osgEarth优先支持：可能包含了关于获取官方支持和社区服务的信息。 osgEarth的文档与代码一起存储在git仓库中，这意味着它是开源的，鼓励用户贡献和改进文档。如果你发现缺少文档或有其他疑问，可以通过参与贡献来帮助完善。 osgEarth是一个强大的工具，它为OpenSceneGraph用户提供了构建3D地理应用的能力，简化了地理数据的处理，且与开放标准兼容，是地理空间领域开发者的有力助手。

osgEarth Documentation, Release 2.10

Argument Description

--out file_name output ﬁle for boundary geometry (default is boundary.txt)

--no-geocentric Skip geocentric reprojection (for ﬂat databases)

--convex-hull calculate a convex hull instead of a full boundary

--verbose print progress to console

--view show result in 3D window

--tolerance N vertices less than this distance apart will be coalesced (0.005)

--precision N output coordinates will have this many signiﬁcant digits (12)

osgearth_overlayviewer

osgearth_overlayviewer is a utility for debugging the overlay decorator capability in osgEarth. It shows two windows,

one with the normal view of the map and another that shows the bounding frustums that are used for the overlay

computations.

1.3.2 Using Earth Files

An Earth File is an XML description of a map. Creating an earth ﬁle is the easiest way to conﬁgure a map and get

up and running quickly. In the osgEarth repository you will ﬁnd dozens of sample earth ﬁles in the tests folder,

covering various topics and demonstrating various features. We encourage you to explore and try them out!

Also see: Earth File Reference

Contents of an Earth File

osgEarth uses an XML based ﬁle format called an Earth File to specify exactly how source data turns into an OSG

scene graph. An Earth File has a .earth extension, but it is XML.

Fundamentally the Earth File allows you to specify:

• The type of map to create (geocentric or projected)

• The image, elevation, vector and model sources to use

• Where the data will be cached

A Simple Earth File

Here is a very simple example that reads data from a GeoTIFF ﬁle on the local ﬁle system and renders it as a geocentric

round Earth scene:

<url>world.tif</url>

</image>

</map>

This Earth File creates a geocentric Map named MyMap with a single GeoTIFF image source called bluemarble.

The driver attribute tells osgEarth which of its plugins to use to use to load the image. (osgEarth uses a plug-in

framework to load different types of data from different sources.)

Some of the sub-elements (under image) are particular to the selected driver. To learn more about drivers and how to

conﬁgure each one, please refer to the Driver Reference Guide.

1.3. User Guide 11

osgEarth Documentation, Release 2.10

Multiple Image Layers

osgEarth supports maps with multiple image sources. This allows you to create maps such as base layer with a

transportation overlay or provide high resolution insets for speciﬁc areas that sit atop a lower resolution base map.

To add multiple images to a Earth File, simply add multiple “image” blocks to your Earth File:

<url>c:/data/bluemarble.tif</url>

</image>

</image>

</map>

The above map provides two images from local data sources using the GDAL driver. Order is important when deﬁning

multiple image sources: osgEarth renders them in the order in which they appear in the Earth File.

Tip: relative paths within an Earth File are interpreted as being relative to the Earth File itself.

Adding Elevation Data

Adding elevation data (sometimes called “terrain data”) to an Earth File is very similar to adding images. Use an

elevation block like so:

<url>c:/data/bluemarble.tif</url>

</image>

</elevation>

</map>

This Earth File has a base bluemarble image as well as a elevation grid that is loaded from a local GeoTIFF ﬁle.

You can add as many elevation layers as you like; osgEarth will combine them into a single mesh.

As with images, order is important - For example, if you have a base elevation data source with low-resolution coverage

of the entire world and a high-resolution inset of a city, you need specify the base data FIRST, followed by the high-

resolution inset.

Some osgEarth drivers can generate elevation grids as well as imagery.

Note: osgEarth only supports single-channel 16-bit integer or 32-bit ﬂoating point data for use in eleva-

tion layers.

12 Chapter 1. Table of Contents

osgEarth Documentation, Release 2.10

Caching

Since osgEarth renders data on demand, it sometimes needs to do some work in order to prepare a tile for display. The

cache exists so that osgEarth can save the results of this work for next time, instead of processing the tile anew each

time. This increases performance and avoids multiple downloads of the same data.

Here’s an example cache setup:

<url>http://readymap.org/readymap/tiles/1.0.0/7/</url>

</image>

<path>c:/osgearth_cache</path>

</cache>

</options>

</map>

This Earth File shows the most basic way to specify a cache for osgEarth. This tells osgEarth to enable caching and to

cache to the folder c:/osgearth_cache. The cache path can be relative or absolute; relative paths are relative to

the Earth File itself.

There are many ways to conﬁgure caching; please refer to the section on Caching for more details.

1.3.3 Caching

Depending on the nature of the source data, osgEarth may have to perform some processing on it before it becomes a

terrain tile. This may include downloading, reprojection, cropping, mosacing, or compositing, to name a few. These

operations can become expensive. By setting up a cache, you can direct osgEarth to store the result of the processing

so that it doesn’t need to do it again the next time the same tile is needed.

Note! osgEarth’s cache uses an internal data storage representation that is not intended to be accessed

through any public API. It’s intended for use ONLY as a transient cache and not at a data publication

format. The structure is subject to change at any time. If you want to publish a data repository, consider

the osgearth_package utility instead!

Setting up a Cache

You can set up a cache in your earth ﬁle. The following setup will automatically activate caching on all your imagery

and elevation layers:

<map>

<path>folder_name</path>

</cache>

In code this would look like this:

1.3. User Guide 13

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osgEarth 2.10 官方文档：地理空间SDK与地形引擎

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