SRELIEF

IHS Shaded Relief

Environments	EASI
Sections	Description Parameters Parameter Details Details Example Related

Description

The SRELIEF script is used to build an RGB image based on an IHS fusion of a DEM channel with a shaded relief map of that channel.

Parameters

SRELIEF is controlled by the following global parameters:

Name	Prompt	Type	Length
FILE	Database File Name	Char	1 - 192
DBIC	Database Input Channel List	Int	1
DBOC	Database Output Channel List	Int	3
LSRC	Light Source Location	Real	0 - 2
PXSZ	Pixel Ground-Size in Metres	Real	0 - 2

Parameter details

FILE

Specifies the name of the PCIDSK file on which the source elevation data exists, and to which the RGB result image should be written.

EASI> FILE="filespec1"

DBIC

Specifies the input elevation channel.

EASI> DBIC = n

DBOC

Specifies the output red, green and blue channels.

EASI> DBOC = red, green, blue

LSRC - Optional

Specifies the azimuth and elevation of the diffuse light source. If defaulted a value of 315,45 will be used.

EASI> LSRC=Aang,Eang

LSRC(1), the azimuth angle, can be any non-negative number; values greater than 359 degrees are treated as MOD(360).
LSRC(2), the elevation angle, must be between 0 and 180 degrees.

PXSZ - Optional

Specifies, in metres, the X and Y dimensions of one pixel on the ground. If PXSZ is not specified, SRELIEF uses the pixel size stored in the database file by CIM, APS, or GEOSET. Correct calculation of the shaded relief depends on proper specification of this value.

EASI> PXSZ=Xsize,Ysize

Details

The SRELIEF task generates an RGB shared relief image from an input image channel. The primary input is a single DEM channel in DBIC, and the results are written to the three channels indicated in the DBOC parameter. The LSRC parameter may be used to control the light source. The PXSZ parameter may be used to establish a relation between the size of a pixel, and an increase of 1.0 in the DEM channel for the purposes of computing the shaded relief.

The SRELIEF task computes a shaded relief value from the input DEM channel using the REL task. This shaded relief image is used as the intensity channel of the resulting IHS image. The hue is established by scaling elevation channel over the range of hue values. The saturation value is a constant value of 128. This IHS image is then converted into RGB in the output channels.

It is often desirable to exaggerate elevation values in order to get a satisfactory display. This can be done reducing the PXSZ value from the real values, essentially a reduction of 50% in the PXSZ value is the same as doubling the elevation values.

Example

Build an RGB shared relief image from the elevation channel on irvine.pix.

EASI> FILE = "irvine.pix"
EASI> DBIC = 10
EASI> DBOC = 7,8,9
EASI> PXSZ = 15,15         | Set pixel size to half the real 30mx30m
                           | size in order to exaggerate elevation.
EASI> RUN SRELIEF

Related topics

The following is a list of related topics.