shade Documentation

SHADE - Create shaded relief image from topographic image
PROGRAMMER: KAY EDWARDS

SHADE can be used to create an image that looks approximately like an
aerial photograph of the topographic image.  The sides of hills will be
shaded or brightened depending on the sun direction, but no shadows will
be cast.  This can be used to get an impression of the shape of the
land.  Other data besides topography, such as gravity or magnetic data,
can be used in this program, as long as it is a continuous data set.

SHADE computes reflectance given any sun elevation and one of 4 sun
directions using the Lommel-Seeliger law:

	REFLECTANCE=1/(1+COS(E)/COSI)

Where: E=the angle between the observer and the slope normal
       I=the angle between the sun and the slope normal

*For this application the observer is at 90 degrees (vertical) and the
sun direction=0, 45, 90 or 135 degrees.

For more detail on shaded-relief images see the reference:

      "Computer-generated Shaded-relief Images"
      R. M. Batson, Kathleen Edwards, and E. M. Eliason;
      Jour. Research U.S. Geol. Survey Vol 3, No. 4,
      July-Aug. 1975, p. 401-408.

INPUT IMAGE FILE NAME

NONE

OUTPUT IMAGE FILE NAME

NONE

SUN ANGLE FROM ZENITH

NONE

SUN DIRECTION (0,45,90,135)

0.

VERTICAL SCALE (KM/DN)

1.

HORIZONTAL SCALE (KM/PIX)

1.

VERTICAL EXAGERATION

1.

STARTING LINE

1

STARTING SAMPLE

1

NUMBER OF LINES

0

NUMBER OF SAMPLES

0

LINE INCREMENT

1.

SAMPLE INCREMENT

1.

ADDITIONAL NOTES:

Parm	Description
FROM	This is the topographic image that is to be shaded. This image may be 8 or 16 bit.
TO	This is the resultant shaded relief file. This image is always 8 bit.
SUN	For SUN=0, the sun is directly overhead. For SUN=90, the sun is on the horizon.
DIRC	0= left to right 45= top left to bottom right 90= top to bottom 135= top right to bottom left
VERT	The vertical scale should be in the same units as the horizontal scale. For example, if vertical scale is in kilometers/density number (KM/DN) then horizontal scale should be in kilometers/pixel (KM/PIX). If vertical scale is in feet/density number, then horizontal scale must be given in feet/pixel.
HORZ	See VERT.
EXAG	This parameter can be used to exaggerate the shaded relief effect. A value greater than 1 will make the slopes appear steeper.
SL	Starting line. The default is 1 which will start the processing with the first line or top of the image.
SS	Starting sample. The default is 1 which will start the processing with the first sample or left side of the image.
NL	Number of lines. The default is 0 which will process all lines of the image.
NS	Number of samples. The default is 0 which will process all samples of the image.
LINC	Line increment. The default is 1.0 which will process each line of the image. LINC=2.0 will process every other line and the output image will have half as many lines as the input. LINC=.5 will process each line twice and the output image will have twice as many lines as the input.
SINC	Sample increment. The default is 1.0 which will process each sample of the image. SINC=2.0 will process every other sample and the output image will have half as many samples as the input. SINC=.5 will process each sample twice and the output image will have twice as many samples as the input.