About the Visualize Elevation process

Legacy:

ArcGIS 10 is the last release of the stand-alone ArcGIS Image Server product. The image service definition (.ISDef) has been replaced by an improved geodatabase data model—the mosaic dataset—which can be published as an image service using the ArcGIS Server Image extension.

The Visualize Elevation process allows you to render (display) elevation data using various methods of visualization. Each is described in the table below.

Elevation visualization methods	Description	Example
Elevation-coded	Color values from the symbology are ascribed to different ranges of elevation values.
Hillshade	A grayscale 3D model of the terrain, with the sun's relative position taken into account for shading the image. This method uses the Altitude and Azimuth properties to specify the sun's position.
Shaded Relief	A color 3D model of the terrain, created by merging the images from the Elevation-coded and Hillshade methods. This method uses the Altitude and Azimuth properties to specify the sun's position.
Slope	A color-coded representation of slope values. Slope represents the rate of change of elevation for each DEM cell. It's the first derivative of a DEM.
Aspect	Identifies the downslope direction of the maximum rate of change in value from each cell to its neighbors. Aspect can be thought of as the slope direction. The values of the output raster will be the compass direction of the aspect.
Curvature	A color-coded representation of curvature values. Curvature represents the rate of change of slope for each DEM cell. It's the second derivative of a DEM.

Visualize Elevation methods

The properties Azimuth and Altitude together indicate the sun's relative position that will be used for creating any 3D model (hillshade or shaded relief). These parameters are ignored for representations that depend only on the actual height values (elevation, slope, aspect, and curvature). Altitude is the sun's angle of elevation above the horizon. A value of 0 degrees indicates that the sun is on the horizon, that is, on the same horizontal plane as the frame of reference. A value of 90 degrees indicates that the sun is directly overhead. By default, the altitude value is 45 degrees.

Azimuth is the sun's relative position along the horizon (in degrees). This position is indicated by the angle of the sun measured clockwise from due north. An azimuth of 0 degrees indicates north, east is 90 degrees, south is 180 degrees, and west is 270 degrees. By default, the azimuth value of 315 degrees (northwest) is used.

Note:

To calculate the slope for a point, you need two pixels around the current pixel. This is not possible at the edges. Therefore, the pixels at the edges are colored black, resulting in a black border around the image. If you add the Visualize Elevation process at the service level, the area of interest will have a black border around it. This is because the area of interest is treated as an image at the service level. If you are applying this process at the raster or raster dataset level, you will not get the black border unless the area of interest is at the edge of the image. This behavior applies to all visualization methods except Elevation-coded.

Defining the symbology

For each of the Visualize Elevation methods, there are several different ways to define the symbology (use of color). There is a default method using predefined color ramps, or you can load a color ramp defined in a file or generate the color ramp on the fly based on some additional settings. These choices are listed below for each method.

Visualization method	Default symbology	Load symbology from a file	Define symbology on the fly
Elevation-coded	no
Hillshade
Shaded Relief	no
Slope
Aspect
Curvature	no

Types of symbology for each method

Default symbology

The default symbology is read from an XML file installed with the software (<Install Directory>\ArcGIS\Image Server\Symbology\DefaultElevationSymbology.xml). A grayscale color ramp is provided for displaying a hillshaded elevation model. The following image displays an elevation model using the default hillshade symbology.

The aspect color ramp displays the following colors based on the direction of the slope:

The following image displays an elevation model using the default aspect symbology:

The slope color ramp is a gradation of blues that displays slope based on the value of the angle in degrees:

The following image displays an elevation model using the default aspect symbology:

Color ramp file

To define the color ramp in a file, you can create a comma-delimited text file (.txt), specifying the elevation value followed by the color expressed as 8-bit red, green, and blue values (elevation value, red, green, blue). For example:

0,170,220,216

1,183,223,209

2,207,232,200

3,221,236,194

4,231,239,188

When specifying the elevation values, arrange them in a sequence from low to high. If you list elevation values in the text file that skip from one number to the next, such as 1 then 5, instead of listing all the values individually (1 2 3 4 5), the color can be graduated between the first and last number for any occurrences of the elevation values in between. Otherwise, the first color will be applied to all the elevation values above it until another color is specified. To make sure the colors are graduated between each other, you must check the Smooth Gradient check box on the Symbology Properties tab.

On the fly

When generating symbology on the fly, you can define the range of elevation values to be computed from the area displayed or define the lower and upper values that will be used to create the color ramp. When using the displayed area, the method that computes the ranges can be either standard deviation or equal intervals. The symbology source you choose will affect the symbology properties available to set.

If you specify to compute the range source from the area of interest using the standard deviation computation method, you can choose

• The first and last colors in the color ramp
• The number of entries in the color ramp that will be used to render the elevation values
• The number of standard deviations that will be used to define the class breaks
• To smoothen the gradient between the colors

If you specify to compute the range source from the area of interest using the equal intervals computation method, you can choose

• The first and last colors in the color ramp
• The number of standard deviations that will be used to define the class breaks
• To smoothen the gradient between the colors

If you specifyto compute the range of source from user-defined height values, you can choose

• The lower and upper height values
• The first and last colors in the color ramp
• The number of entries in the color ramp that will be used to render the elevation values
• To smoothen the gradient between the colors

When using the Hillshade method to display your elevation model, only a grayscale color ramp is used; therefore, you can't choose a first or last color in your color ramps. However, you have all the other options as described above for each setting.

The image on the left displays an elevation model using the Elevation-coded symbology method. The image on the right displays the same elevation model using the Shaded Relief method. Both color ramps are computed using the Compute from AOI option with the standard deviation method. The first color in the color ramp is brown, and the last color is yellow.

Input and output criteria

The following table lists the input and output number of bands, pixel types, and color spaces for each of the Visualize Elevation methods.

Method	Number of input bands	Input bit depth	Input pixel type	Input color space	Number of output bands	Output bit depth	Output pixel type	Output color space
Elevation-coded	1	32	Elevation	Unknown	1	8	Unsigned 8-bit	Grayscale
Hillshade	1	32	Elevation	Unknown	3	8	Unsigned 8-bit	Grayscale
Shaded Relief	1	32	Elevation	Unknown	3	8	Unsigned 8-bit	RGB
Slope	1	32	Elevation	Unknown	3	8	Unsigned 8-bit	RGB
Aspect	1	32	Elevation	Unknown	3	8	Unsigned 8-bit	RGB
Curvature	1	32	Elevation	Unknown	3	8	Unsigned 8-bit	RGB

Inputs and outputs for each method