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Visibility

Available with Spatial Analyst license.

Available with 3D Analyst license.

Summary

Determines the raster surface locations visible to a set of observer features, or identifies which observer points are visible from each raster surface location.

Illustration

Visibility with Frequency option illustration
Visibility output with the Frequency option, displayed on a hillshaded elevation surface
Visibility with Observers option illustration
Visibility output with the Observers option, displayed on a hillshaded elevation surface

Usage

  • This tool supports two visibility analysis types, Frequency and Observers, which is controlled by the Analysis type tool parameter. For the first type, the tool determines which raster surface locations are visible to a set of observers. For the other, it identifies which observers are visible from each raster surface location.

  • If the input raster contains undesirable noise caused by sampling errors, you can smooth the raster with a low-pass filter, such as the Mean option of Focal Statistics, before running this tool.

  • The visibility of each cell center is determined by comparing the altitude angle to the cell center with the altitude angle to the local horizon. The local horizon is computed by considering the intervening terrain between the point of observation and the current cell center. If the point lies above the local horizon, it is considered visible.

  • An optional above-ground-level (AGL) output raster is provided by the tool. Each cell on the AGL output raster records the minimum height that needs to be added to that cell to make it visible by at least one observer.

    When the input observer features contain multiple observers, the output value is the minimum of the AGL values from all of the individual observers.

  • Use the observer parameters to gain more control over the visibility analysis process. For example, through the observer offset parameter, you may specify an offset to the observer elevation in the visibility analysis.

  • When the input raster needs to be resampled, the bilinear technique will be used. An example of when an input raster may be resampled is when the output coordinate system, extent, or cell size is different from that of the input.

  • See Analysis environments and Spatial Analyst for additional details on the geoprocessing environments that apply to this tool.

Syntax

Visibility (in_raster, in_observer_features, {out_agl_raster}, {analysis_type}, {nonvisible_cell_value}, {z_factor}, {curvature_correction}, {refractivity_coefficient}, {surface_offset}, {observer_elevation}, {observer_offset}, {inner_radius}, {outer_radius}, {horizontal_start_angle}, {horizontal_end_angle}, {vertical_upper_angle}, {vertical_lower_angle})
ParameterExplanationData Type
in_raster

The input surface raster.

Raster Layer
in_observer_features

The feature class that identifies the observer locations.

The input can be point or polyline features.

Feature Layer
out_agl_raster
(Optional)

The output above-ground-level (AGL) raster.

The AGL result is a raster where each cell value is the minimum height that must be added to an otherwise nonvisible cell to make it visible by at least one observer.

Cells that were already visible will have a value of 0 in this output raster.

Raster Dataset
analysis_type
(Optional)

The visibility analysis type.

  • FREQUENCY The output records the number of times that each cell location in the input surface raster can be seen by the input observation locations (as points, or as vertices for polyline observer features). This is the default.
  • OBSERVERS The output identifies exactly which observer points are visible from each raster surface location.
String
nonvisible_cell_value
(Optional)

Value assigned to non-visible cells.

  • ZERO 0 is assigned to nonvisible cells. This is the default.
  • NODATA NoData is assigned to nonvisible cells.
Boolean
z_factor
(Optional)

Number of ground x,y units in one surface z unit.

The z-factor adjusts the units of measure for the z units when they are different from the x,y units of the input surface. The z-values of the input surface are multiplied by the z-factor when calculating the final output surface.

If the x,y units and z units are in the same units of measure, the z-factor is 1. This is the default.

If the x,y units and z units are in different units of measure, the z-factor must be set to the appropriate factor, or the results will be incorrect. For example, if your z units are feet and your x,y units are meters, you would use a z-factor of 0.3048 to convert your z units from feet to meters (1 foot = 0.3048 meter).

Double
curvature_correction
(Optional)

Allows correction for the earth's curvature.

  • FLAT_EARTHNo curvature correction will be applied. This is the default.
  • CURVED_EARTHCurvature correction will be applied.
Boolean
refractivity_coefficient
(Optional)

Coefficient of the refraction of visible light in air.

The default value is 0.13.

Double
surface_offset
(Optional)

This value indicates a vertical distance to be added to the z-value of each cell as it is considered for visibility. It should be a positive integer or floating-point value.

You can select a field in the input observers dataset, or you can specify a numerical value.

By default, a numerical field OFFSETB is used if it exists in the input observer features attribute table. You may overwrite it by specifying another numerical field or a value.

If this parameter is unspecified and the default field does not exist in the input observer features attribute table, it defaults to 0.

String
observer_elevation
(Optional)

This value is used to define the surface elevations of the observer points or vertices.

You can select a field in the input observers dataset, or you can specify a numerical value.

By default, a numerical field SPOT is used if it exists in the input observer features attribute table. You may overwrite it by specifying another numerical field or a value.

If this parameter is unspecified and the default field does not exist in the input observer features attribute table, it will be estimated through bilinear interpolation with the surface elevation values in the neighboring cells of the observer location.

String
observer_offset
(Optional)

This value indicates a vertical distance to be added to the observer elevation. It should be a positive integer or floating-point value.

You can select a field in the input observers dataset, or you can specify a numerical value.

By default, a numerical field OFFSETA is used if it exists in the input observer features attribute table. You may overwrite it by specifying another numerical field or a value.

If this parameter is unspecified and the default field does not exist in the input observer features attribute table, it defaults to 1.

String
inner_radius
(Optional)

This value defines the start distance from which visibility is determined. Cells closer than this distance are not visible in the output but can still block visibility of the cells between inner radius and outer radius.

It can be a positive or negative integer or floating point value. If it is a positive value, then it is interpreted as three-dimensional, line-of-sight distance. If it is a negative value, then it is interpreted as two-dimensional planimetric distance.

You can select a field in the input observers dataset, or you can specify a numerical value.

By default, a numerical field RADIUS1 is used if it exists in the input observer features attribute table. You may overwrite it by specifying another numerical field or a value.

If this parameter is unspecified and the default field does not exist in the input observer features attribute table, it defaults to 0.

String
outer_radius
(Optional)

This value defines the maximum distance from which visibility is determined. Cells beyond this distance are excluded from the analysis.

It can be a positive or negative integer or floating point value. If it is a positive value, then it is interpreted as three-dimensional, line-of-sight distance. If it is a negative value, then it is interpreted as two-dimensional planimetric distance.

You can select a field in the input observers dataset, or you can specify a numerical value.

By default, a numerical field RADIUS2 is used if it exists in the input observer features attribute table. You may overwrite it by specifying another numerical field or a value.

If this parameter is unspecified and the default field does not exist in the input observer features attribute table, it defaults to infinity.

String
horizontal_start_angle
(Optional)

This value defines the start angle of the horizontal scan range. The value should be specified in degrees from 0 to 360, either as integer or floating point, with 0 oriented to north. The default value is 0.

You can select a field in the input observers dataset, or you can specify a numerical value.

By default, a numerical field AZIMUTH1 is used if it exists in the input observer features attribute table. You may overwrite it by specifying another numerical field or a value.

If this parameter is unspecified and the default field does not exist in the input observer features attribute table, it defaults to 0.

String
horizontal_end_angle
(Optional)

This value defines the end angle of the horizontal scan range. The value should be specified in degrees from 0 to 360, either as integer or floating point, with 0 oriented to north. The default value is 360.

You can select a field in the input observers dataset, or you can specify a numerical value.

By default, a numerical field AZIMUTH2 is used if it exists in the input observer features attribute table. You may overwrite it by specifying another numerical field or a value.

If this parameter is unspecified and the default field does not exist in the input observer features attribute table, it defaults to 360.

String
vertical_upper_angle
(Optional)

This value defines the upper vertical angle limit of the scan above a horizontal plane. The value should be specified in degrees from 0 to 90, which can be integer or floating point.

You can select a field in the input observers dataset, or you can specify a numerical value.

By default, a numerical field VERT1 is used if it exists in the input observer features attribute table. You may overwrite it by specifying another numerical field or a value.

If this parameter is unspecified and the default field does not exist in the input observer features attribute table, it defaults to 90.

String
vertical_lower_angle
(Optional)

This value defines the lower vertical angle limit of the scan below a horizontal plane. The value should be specified in degrees from -90 to 0, which can be integer or floating point.

You can select a field in the input observers dataset, or you can specify a numerical value.

By default, a numerical field VERT2 is used if it exists in the input observer features attribute table. You may overwrite it by specifying another numerical field or a value.

If this parameter is unspecified and the default field does not exist in the input observer features attribute table, it defaults to -90.

String

Return Value

NameExplanationData Type
out_raster

The output raster.

The output will either record the number of times that each cell location in the input surface raster can be seen by the input observation locations (the frequency analysis type), or record which observer locations are visible from each cell in the raster surface (the observers type).

Raster

Code sample

Visibility example 1 (Python window)

This example determines surface locations visible to a set of observers defined in a shapefile.

import arcpy
from arcpy import env
from arcpy.sa import *

env.workspace = "c:/sapyexamples/data"

outvis = arcpy.sa.Visibility("elevation", "observers.shp", "c:/sapyexamples/output/aglout1",
                            "FREQUENCY", "NODATA", "1", "CURVED_EARTH", "0.13",
                            "OFFSETB", "SPOT", "OFFSETA", "RADIUS1", "RADIUS2",
                            "AZIMUTH1", "AZIMUTH2", "VERT1", "VERT2")

outvis.save("c:/sapyexamples/output/visiout1")
Visibility example 2 (stand-alone script)

This example determines which observers are visible at each surface location.

# Name: Visibility_Ex_02.py
# Description: Determines the raster surface locations visible to a set of
#                     observer features.
# Requirements: Spatial Analyst Extension

# Import system modules
import arcpy
from arcpy import env
from arcpy.sa import *

# Set environment settings
env.workspace = "c:/sapyexamples/data"

# set local variables
inRaster = "elevation"
inObserverFeatures = "observers.shp"
aglOutput = "c:/sapyexamples/output/aglout1"
analysisType = "OBSERVERS"
nonVisibleValue = "ZERO"
zFactor = 1
useEarthCurvature = "CURVED_EARTH"
refractivityCoefficient = 0.13
surfaceOffset = 500
observerElevation = 2000
observerOffset = 500
innerRadius = 20000
outerRadius = 100000
horizStartAngle = 45
horizEndAngle = 215
vertUpperAngle = 5
vertLowerAngle = -5

# Check out the ArcGIS Spatial Analyst extension license
arcpy.checkOutExtension("Spatial")

# Execute Visibility
outvis = arcpy.sa.Visibility(inRaster, inObserverFeatures, algOutput, analysisType,
                            nonVisibleValue, zFactor, useEarthCurvature,
                            refractivityCoefficient, surfaceOffset, observerElevation,
                            observerOffset, innerRadius, outerRadius, horizStartAngle,
                            horizEndAngle, vertUpperAngle, vertLowerAngle)

# Save the output
outvis.save("c:/sapyexamples/output/visiout1")

Licensing information

  • ArcGIS Desktop Basic: Requires Spatial Analyst or 3D Analyst
  • ArcGIS Desktop Standard: Requires Spatial Analyst or 3D Analyst
  • ArcGIS Desktop Advanced: Requires Spatial Analyst or 3D Analyst

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