Observer Points (Spatial Analyst)

Summary

Identifies which observer points are visible from each raster surface location.

Usage

• Determining observer points is a computer-intensive process. The processing time is dependent on the resolution. For preliminary studies, you may want to use a coarser cell size to reduce the number of cells in the input. Use the full resolution raster when the final results are ready to be generated.

• 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.

Syntax

ObserverPoints (in_raster, in_observer_point_features, {z_factor}, {curvature_correction}, {refractivity_coefficient})
 Parameter Explanation Data Type in_raster The input surface raster. Raster Layer in_observer_point_features The point feature class that identifies the observer locations. The maximum number of points allowed is 16. Feature Layer 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_EARTH — No curvature correction will be applied. This is the default. CURVED_EARTH — Curvature correction will be applied. Boolean refractivity_coefficient(Optional) Coefficient of the refraction of visible light in air.The default value is 0.13. Double

Return Value

 Name Explanation Data Type out_raster The output raster.The output identifies exactly which observer points are visible from each raster surface location. Raster

Code Sample

ObserverPoints example 1 (Python window)

This example identifies exactly which observer points are visible from each raster surface location.

```import arcpy
from arcpy import env
from arcpy.sa import *
env.workspace = "C:/sapyexamples/data"
outObsPoints = ObserverPoints("elevation","observers.shp", 1, "CURVED_EARTH", 0.13)
outObsPoints.save("C:/sapyexamples/output/outobspnt01")```
ObserverPoints example 2 (stand-alone script)

This example identifies exactly which observer points are visible from each raster surface location.

```# Name: ObserverPoints_Ex_02.py
# Description:  Identifies exactly which observer points are visible
# from each raster surface location.
# Requirements: Spatial Analyst Extension
# Author: ESRI

# 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"
inObsPoints = "observers.shp"
zFactor = 1
useEarthCurv = "CURVED_EARTH"
refractionVal = 0.13

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

# Execute ObserverPoints
outObsPoints = ObserverPoints(inRaster, inObsPoints, zFactor,
useEarthCurv, refractionVal)

# Save the output
outObsPoints.save("C:/sapyexamples/output/outobspnt02")```

Licensing Information

ArcView: Requires Spatial Analyst or 3D Analyst
ArcEditor: Requires Spatial Analyst or 3D Analyst
ArcInfo: Requires Spatial Analyst or 3D Analyst

6/29/2011