ENVI 头文件格式说明

The ENVI Header Format

The ENVI header file contains information ENVI uses to read an image data

file. ENVI typically creates a header file the first time you access a data file in a

format that it does not automatically recognize. You enter the required

information in the Header Info dialog, which appears when the file is opened

(see Creating Header Files). You can later edit the information using the Edit

ENVI Header option (Editing Header Files).

You can also generate an ENVI header outside ENVI using a text editor. The

file must start with the text string

ENVI for ENVI to recognize it as a native file

header. Keywords within the file indicate critical file information. You can add

comments to the file by inserting a line with a semicolon as the first character.

ENVI ignores these lines when parsing the header file. Comments can appear

anywhere within a header file, but they must be on their own line, and the

semicolon must be the first character of that line. Comments cannot follow a

keyword/value pair.

A description of the keywords (in alphabetical order) for an ENVI header file

follows. See Example ENVI Header File for an example header file.

Table 5-1: Header File Keywords

Field Description

band names

Allows entry of specific names for each band of an image.

bands

bbl

The number of bands per image file.

Lists the bad band multiplier values of each band in an

image, typically 0 for bad bands and 1 for good bands.

The order of the bytes in integer, long integer, 64-bit integer,

unsigned 64-bit integer, floating point, double precision, and

complex data types. Use one of the following:

•

byte order

•

Byte order=0 (Host (Intel) in the Header Info dialog)

is least significant byte first (LSF) data (DEC and

MS-DOS systems).

Byte order=1 (Network (IEEE) in the Header Info

dialog) is most significant byte first (MSF) data (all

other platforms).

class lookup

This keyword pertains to classification files. It lists RGB color

definitions for each respective class, and class names.

class names

classes

This keyword pertains to classification files. It lists the

classification names.

This keyword pertains to classification files. It defines the

number of classes, including the unclassified.

Specifies the values to calculate from a complex image and

to use when displaying the image, calculating statistics for

the image, or writing the image to a new file. Values include

Real,

Imaginary,

Power,

Magnitude, and

Phase.

The default value is

Phase.

When you save a georeferenced file to ENVI raster format,

ENVI adds a coordinate system string field to the header file.

It lists the parameters used for a geographic coordinate

system or projected coordinate system. Following are some

examples:

A geographic coordinate system (for example,

Geographic Lat/Lon) string contains the word

GEOGCS and

lists the coordinate system name, datum, spheroid, prime

meridian, and units:

complex

function

coordinate system string =

GEOGCS["GCS_WGS_1984",

DATUM["D_WGS_1984",

SPHEROID["WGS_1984",6378137.0,298.257223563]],

PRIMEM["Greenwich",0.0],

coordinate

UNIT["Degree",0.9433]]

system

string

A projected coordinate system string contains the word

PROJCS and lists all of the geographic coordinate system

parameters, plus detailed parameters that describe the

projected coordinate system:

coordinate system string =

PROJCS["WGS_1984_South_Georgia_Lambert",

GEOGCS["GCS_WGS_1984",

DATUM["D_WGS_1984",

SPHEROID["WGS_1984",6378137.0,298.257223563]],

PRIMEM["Greenwich",0.0],

UNIT["Degree",0.9433]],

PROJECTION["Lambert_Conformal_Conic"],

PARAMETER["False_Easting",0.0],

PARAMETER["False_Northing",0.0],

PARAMETER["Central_Meridian",-37.0],

PARAMETER["Standard_Parallel_1",-54.0],

PARAMETER["Standard_Parallel_2",-54.75],

PARAMETER["Latitude_Of_Origin",-55.0],

UNIT["Meter",1.0]]

Refer to the ITT Visual Information Solutions Tech Tips for a

list of predefined geographic and projected coordinate

system strings:

coordinate

1. Go to /services/.

system

2. In the Enter Keyword field, type projection engine.

string

3. Click Submit.

4. In the search results, open the Tech Tip titled, "ESRI

Projection Engine Reference v1.0."

data gain

values

Gain values for each band.

Currently used only in ENVI programming

more information).

data ignore

(see ENVI_FILE_QUERY in the ENVI Reference Guide for

value

data offset

Offset values for each band.

values

The type of data representation, where 1=8-bit byte;

2=16-bit signed integer; 3=32-bit signed long integer;

4=32-bit floating point; 5=64-bit double-precision floating

point; 6=2x32-bit complex, real-imaginary pair of double

precision; 9=2x64-bit double-precision complex,

real-imaginary pair of double precision; 12=16-bit unsigned

integer; 13=32-bit unsigned long integer; 14=64-bit signed

long integer; and 15=64-bit unsigned long integer.

If set, indicates which band numbers to automatically load

into the Available Bands List gray scale or R, G, and B fields

every time the file is opened. By default, a new image is

automatically loaded when a file that has default bands

defined in its header is opened. If only one band number is

used, then ENVI loads a gray scale image.

Determines what type of stretch (% linear, linear range,

Gaussian, equalization, square root) to use when ENVI

displays the image.

data type

default

bands

default

stretch

dem band

Path and filename of a DEM that you associate with an

image.

Index (starting at 1) of a selected DEM band that you

associate with an image. The

dem

band is not written if the

DEM file contains a single band, or if the first band of an

image was chosen. In these cases, the

dem

band value

defaults to 0. See Editing ENVI File Headers in the ENVI

User's Guide.

A character string describing the image or the processing

performed.

The ENVI-defined file type, such as a certain data format

and processing result. The available file types are listed in

the

file (see ENVI File Type File). The file

type ASCII string must match an entry in the

file verbatim, including case.

Lists full-width-half-maximum (FWHM) values of each band

in an image. Units should be the same as those used for

wavelength and set in the wavelength units parameter.

Geographic corners for non-georeferenced files. You can

enter between one and four pixel locations and their

corresponding latitudes and longitudes. Following is an

example:

dem file

description

file type

fwhm

geo points = {

1.0000, 1.0000, 32.89380137,

-117.07201460,

1002.0000, 1.0000, 32.87364744,

-116.95855862,

1.0000, 1002.0000, 32.80628336,

-117.09960891,

1002.0000, 1002.0000, 32.78615422,

-116.98625969}

header

offset

The number of bytes of imbedded header information

present in the file (for example, 128 bytes for ERDAS

7.5

.lan files). ENVI skips these bytes when reading the

file.

geo points

interleave

Refers to whether the data are BSQ, BIP, or BIL.

lines

The number of lines per image for each band.

Lists geographic coordinates information in the order of

projection name (UTM), reference pixel x location (in file

coordinates), pixel y, pixel easting, pixel northing, x pixel

size, y pixel size, projection zone, North or South (UTM

only).

map info Note - In ENVI, pixel values always refer to the upper-left

corner of the pixel. Map coordinates also typically refer to

the upper-left corner of the pixel. However, if you entered

"magic pixel" coordinates in the ENVI header, the map

coordinates would refer to the x,y coordinates entered. For

example, x=1.5, y=1.5 would make the map coordinates

refer to the center of the pixel.

Indicates x and y pixel size in meters for non-georeferenced

files.

The number of extra bytes to skip at the beginning and

the ENVI User's Guide.

pixel size

major frame

ending of the major frame. See Editing ENVI File Headers in

offsets

minor frame

ending of the minor frame. See Editing ENVI File Headers in

offsets

the ENVI User's Guide.

Describes user-defined projection information. This keyword

is added to the ENVI header file if a the file uses a

projection

user-defined projection instead of a standard projection.

info

ENVI uses this information to read the file on machines that

do not contain this user-defined projection in the

map_projmap_ file.

The number of extra bytes to skip at the beginning and

reflectance

The value that, when divided into your data, would scale it

scale factor

from 0-1 reflectance.

rpc info

Lists rational polynomial coefficient (RPC) geolocation

information if your input file has this associated information.

See Editing ENVI File Headers in the ENVI User's Guide.

The number of samples (pixels) per image line for each

band.

samples

Instrument types, such as Landsat TM, SPOT, RADARSAT,

and so on. The available sensor types are the

sensor type

file described in ENVI Sensor File. The

sensor type ASCII string defined here must match one of the

entries in the

file verbatim, including case.

spectra

names

This keyword pertains to spectral library files only. It

contains a comma-separated list of ASCII names enclosed

in {curly brackets}.

Lists the center wavelength values of each band in an

image. Units should be the same as those used for the

wavelength

fwhm field (described next) and set in the wavelength units

parameter.

wavelength

Text string indicating the wavelength units.

units

Defines the image coordinates for the upper-left hand pixel

in the image. Images that are spatial subsets of larger

images often use an image coordinate system that

references the parent (or larger) image so that you can link

and dynamically overlay the two images. The default values

are (1,1) so that the upper-left hand pixel has an image

coordinate of (1,1).

Note - Changing these values does not affect the way ENVI

reads the image data from the file.

x start and

y start

z plot

average

Values indicate the number of pixels in the x and y directions

to average for Z plots.

Values indicating the default minimum and maximum values

for Z plots.

Allows entry of specific x and y axis titles for Z plots.

z plot range

z plot

titles

Example ENVI Header File

A typical ENVI header file looks like this:

ENVI

description = {

Registration Result. Method1st degree Polynomial w/ nearest

neighbor [Wed Dec 20 23:59:19 1995] }

samples = 709

lines = 946

bands = 7

header offset = 0

file type = ENVI Standard

data type = 1

interleave = bsq

sensor type = Landsat TM

byte order = 0

map info = {UTM, 1, 1, 295380.000, 4763640.000, 30.000000,

30.000000, 13, North}

z plot range = {0.00, 255.00}

z plot titles = {Wavelength, Reflectance}

pixel size = {30.000000, 30.000000}

default stretch = 5.0% linear

band names = {

Warp (Band 1:rs_), Warp (Band 2:rs_), Warp (Band

3:rs_), Warp (Band 4:rs_), Warp (Band 5:rs_),

Warp (Band 6:rs_), Warp (Band 7:rs_)}

wavelength = {

0.485000, 0.560000, 0.660000, 0.830000, 1.650000, 11.400000,

2.215000}

fwhm = {

0.070000, 0.080000, 0.060000, 0.140000, 0.200000, 2.100000,

0.270000}

Classification results files include the following additional keywords:

classes = 4

class lookup = { 0, 0, 0,255, 0, 0, 0,255, 0,255,255, 0}

class names = {

Unclassified,

region 1,

region 2,

region 3}

Spectral library files include the following additional keywords:

spectra names = {

ACTINOLITE IN-4A, ALBITE TS-6A, ALMANDINE GARNET NS-4A, ALUNITE

SO-4A,

AMBLYGONITE P-3A, ANALCIME TS-18A, ANATASE SYNTHETIC O-12A,

ANDESINE TS-4A, ANGLESITE SO-10A, ANHYDRITE SO-1A, ANORTHITE TS-

5A,

ANTHOPHYLLITE IN-8A, ANTLERITE SO-11A, APATITE P-1A, APHTHITALITE

SO-9A}