GeoTIFF规格说明文档

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"这篇文档是关于GeoTIFF文件格式的说明，主要涵盖了GeoTIFF的规范版本、修改日期以及作者信息。它详细介绍了GeoTIFF的背景和参与修订的专家团队，同时也提到了与TIFF实现相关的讨论人员，以及提供投影、地理编码数据库和地理学有价值信息的贡献者。此外，还提供了GeoTIFF邮件列表的订阅信息，用于讨论和获取GeoTIFF的相关更新。" GeoTIFF是一种特殊的TIFF（Tagged Image File Format）图像文件格式，专为存储带有地理参考信息的图像而设计。它允许在图像数据中嵌入地理坐标系统、投影信息和其他空间元数据，使图像能够精确地对应到地球表面的位置。GeoTIFF格式的出现解决了传统TIFF图像无法直接关联地理空间信息的问题。 GeoTIFF的规范版本为1.8.2，最后一次修改时间为1995年11月10日。该格式的开发和修订由来自Jet Propulsion Laboratory的Niles Ritter和SPOT Image Corp的Mike Ruth等人共同完成，并得到了GeoTIFF工作小组的广泛参与和贡献。 GeoTIFF的重要特性包括： 1. **地理坐标系统集成**：GeoTIFF可以内嵌WGS84或其他大地坐标系统，确保图像像素与地球表面的地理位置相匹配。 2. **投影信息**：支持多种投影方法，如UTM、Mercator、Lambert Conformal Conic等，这些信息被编码在文件中，使得图像可以在不同的坐标系之间转换。 3. **元数据**：除了图像数据，GeoTIFF还可以包含关于数据采集、处理、分辨率、时间戳等丰富的元数据，这对于地理信息系统（GIS）应用至关重要。 4. **兼容性**：GeoTIFF是在标准TIFF格式基础上扩展的，这意味着它可以被许多图像处理软件支持，同时也能够被GIS软件识别和处理。 5. **分块存储**：GeoTIFF支持图像分块，这有利于大文件的处理和传输，提高了读写效率。 6. **压缩选项**：如同TIFF，GeoTIFF也支持无损或有损压缩，如LZW或JPEG，以减少文件大小。 7. **自定义扩展**：用户可以通过私有标签来添加自定义信息，满足特定需求。 GeoTIFF格式的邮件列表geotiff@tazboy.jpl.nasa.gov提供了一个社区平台，供开发者、用户和爱好者交流GeoTIFF的实现、问题和新进展。通过订阅geotiff-request@tazboy.jpl.nasa.gov，用户可以加入这个讨论组，获取最新的GeoTIFF相关信息和更新。 GeoTIFF文件格式是GIS领域中的一个重要工具，它将图像数据与地理空间信息紧密结合，使得图像数据在地图制作、遥感分析、地形建模等领域有着广泛的应用。这份文档是理解GeoTIFF格式的关键，对于进行地理空间数据处理的工作者来说，它是必不可少的参考资料。

as point measurements at the vertices of a grid, and not in the

interior of a cell.

2.5.2.2 Raster Space

The choice of origin for raster space is not entirely arbitrary, and

depends upon the nature of the data collected. Raster space coordinates

shall be referred to by their pixel types, i.e., as "PixelIsArea" or

"PixelIsPoint".

Note: For simplicity, both raster spaces documented below use a fixed

pixel size and spacing of 1. Information regarding the visual

representation of this data, such as pixels with non-unit aspect

ratios, scales, orientations, etc, are best communicated with the TIFF

6.0 standard tags.

+----------------------------------+

"PixelIsArea" Raster Space

The "PixelIsArea" raster grid space R, which is the default, uses

coordinates I and J, with (0,0) denoting the upper-left corner of the

image, and increasing I to the right, increasing J down. The first

pixel-value fills the square grid cell with the bounds:

top-left = (0,0), bottom-right = (1,1)

and so on; by extension this one-by-one grid cell is also referred to

as a pixel. An N by M pixel image covers an are with the mathematically

defined bounds (0,0),(N,M).

(0,0)

+---+---+-> I

| * | * |

+---+---+ Standard (PixelIsArea) TIFF Raster space R,

| (1,1) (2,1) showing the areas (*) of several pixels.

+----------------------------------+

"PixelIsPoint" Raster Space

The PixelIsPoint raster grid space R uses the same coordinate axis

names as used in PixelIsArea Raster space, with increasing I to the

right, increasing J down. The first pixel-value however, is realized as

a point value located at (0,0). An N by M pixel image consists of

points which fill the mathematically defined bounds (0,0),(N-1,M-1).

Geographic Coordinate Systems are those that relate angular latitude

and longitude (and optionally geodetic height) to an actual point on

the earth. The process by which this is accomplished is rather complex,

and so we describe the components of the process in detail here.

+----------------------------------+

Ellipsoidal Models of the Earth

The geoid - the earth stripped of all topography - forms a reference

surface for the earth. However, because it is related to the earth's

gravity field, the geoid is a very complex surface; indeed, at a

detailed level its description is not well known. The geoid is

therefore not used in practical mapping.

It has been found that an oblate ellipsoid (an ellipse rotated about

its minor axis) is a good approximation to the geoid and therefore a

good model of the earth. Many approximations exist: several hundred

ellipsoids have been defined for scientific purposes and about 30 are

in day to day use for mapping. The size and shape of these ellipsoids

can be defined through two parameters. Geotiff requires one of these to

the semi-major axis (a),

and the second to be either

the inverse flattening (1/f)

the semi-minor axis (b).

Historical models exist which use a spherical approximation; such

models are not recommended for modern applications, but if needed the

size of a model sphere may be defined by specifying identical values

for the semimajor and semiminor axes; the inverse flattening cannot be

used as it becomes infinite for perfect spheres.

Other ellipsoid parameters needed for mapping applications, for example

the square of the eccentricity, can easily be calculated by an

application from the two defining parameters. Note that Geotiff uses

the modern geodesy convention for the symbol (b) for the semi-minor

axis. No provision is made for mapping other planets in which a tri-

dimensional (triaxial) ellipsoid might be required, where (b) would

represent the semi-median axis and (c) the semi-minor axis.

Numeric codes for ellipsoids regularly used for earth-mapping are

included in the Geotiff reference lists.

+----------------------------------+

Latitude and Longitude

The coordinate axes of the system referencing points on an ellipsoid

are called latitude and longitude. More precisely, geodetic latitude

and longitude are required in this Geotiff standard. A discussion of

the several other types of latitude and longitude is beyond the scope

of this document as they are not required for conventional mapping.

Latitude is defined to be the angle subtended with the ellipsoid's

equatorial plane by a perpendicular through the surface of the

ellipsoid from a point. Latitude is positive if north of the equator,

negative if south.

Longitude is defined to be the angle measured about the minor (polar)

axis of the ellipsoid from a prime meridian (see below) to the meridian

through a point, positive if east of the prime meridian and negative if

west. Unlike latitude which has a natural origin at the equator, there

is no feature on the ellipsoid which forms a natural origin for the

measurement of longitude. The zero longitude can be any defined

meridian. Historically, nations have used the meridian through their

national astronomical observatories, giving rise to several prime

meridians. By international convention, the meridian through Greenwich,

England is the standard prime meridian. Longitude is only unambiguous

if the longitude of its prime meridian relative to Greenwich is given.

Prime meridians other than Greenwich which are sometimes used for earth

mapping are included in the Geotiff reference lists.

+----------------------------------+

Geodetic Datums

As well as there being several ellipsoids in use to model the earth,

any one particular ellipsoid can have its location and orientation

relative to the earth defined in different ways. If the relationship

between the ellipsoid and the earth is changed, then the geographical

coordinates of a point will change.

Conversely, for geographical coordinates to uniquely describe a

location the relationship between the earth and the ellipsoid must be

defined. This relationship is described by a geodetic datum. An exact

geodetic definition of geodetic datums is beyond the current scope of

Geotiff. However the Geotiff standard requires that the geodetic datum

being utilized be identified by numerical code. If required, defining

parameters for the geodetic datum can be included as a citation.

+----------------------------------+

Defining Geographic Coordinate Systems

In summary, geographic coordinates are only unique if qualified by the

code of the geographic coordinate system to which they belong. A

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