Visibility (Spatial Analyst)
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.
Usage
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This tool supports two visibility analysis types, FREQUENCY and OBSERVERS, which is controlled by the Analysis type tool parameter. For the FREQUENCY analysis type, the tool determines which raster surface locations are visible to a set of observers. For OBSERVERS, 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.
Syntax
| Parameter | Explanation | Data 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 |
analysis_type (Optional) |
The visibility analysis type.
| String |
nonvisible_cell_value (Optional) | Value assigned to non-visible 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.
| 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 (in surface units) 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. It can be a field in the input observer features dataset or 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 constant. If this parameter is unspecified and the default field does not exist in the input observer features attribute table, it defaults to 0. | Field | Constant |
observer_elevation (Optional) |
This value is used to define the surface elevations of the observer points or vertices. It can be a field in the input observer features dataset or 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 constant. 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. | Field | Constant |
observer_offset (Optional) |
This value indicates a vertical distance (in surface units) to be added to observer elevation. It should be a positive integer or floating point value. It can be a field in the input observer features dataset or 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 constant. If this parameter is unspecified and the default field does not exist in the input observer features attribute table, it defaults to 1. | Field | Constant |
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. It can be a field in the input observer features dataset or 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 constant. If this parameter is unspecified and the default field does not exist in the input observer features attribute table, it defaults to 0. | Field | Constant |
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. It can be a field in the input observer features dataset or 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 constant. If this parameter is unspecified and the default field does not exist in the input observer features attribute table, it defaults to infinity. | Field | Constant |
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, with 0 oriented to north. The default value is 0. It can be a field in the input observer features dataset or 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 constant. If this parameter is unspecified and the default field does not exist in the input observer features attribute table, it defaults to 0. | Field | Constant |
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, with 0 oriented to north. The default value is 360. It can be a field in the input observer features dataset or 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 constant. If this parameter is unspecified and the default field does not exist in the input observer features attribute table, it defaults to 360. | Field | Constant |
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. It can be a field in the input observer features dataset or 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 constant. If this parameter is unspecified and the default field does not exist in the input observer features attribute table, it defaults to 90. | Field | Constant |
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. It can be a field in the input observer features dataset or 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 constant. If this parameter is unspecified and the default field does not exist in the input observer features attribute table, it defaults to -90. | Field | Constant |
Return Value
| Name | Explanation | Data 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 (FREQUENCY option), or record which observer locations are visible from each cell in the raster surface (OBSERVERS option). | Raster |
Code Sample
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")
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")