# ATan (Image Analyst)

## Summary

Calculates the inverse tangent of cells in a raster.

## Usage

• In mathematics, all trigonometric functions have a defined range of valid input values called the domain. The output values from each function also has a defined range. For this tool the following are true:

• The Domain is: -∞ < [in_value] < ∞

• The Range is: -pi/2 ≤ [out_value] ≤ pi/2

Note that -∞ and ∞ represent the smallest negative and largest positive value supported by the particular raster format, respectively.

• The input values to this tool are interpreted as unitless.

• Output values are always floating point, regardless of the input data type.

• The output values from this tool are in radians. To use degrees instead, the resulting raster must be multiplied by the radians-to-degrees conversion factor of 180/pi, or approximately 57.296.

For further assistance, a procedure to follow and examples of converting output in radians to degrees are available.

• If the input is a multiband raster, the output will be a multiband raster. The tool will perform the operation on each band in the input.

• In ArcPy, if the input is a multidimensional raster, all slices from all variables will be processed, and the output will be a multidimensional raster.

## Parameters

 Label Explanation Data Type Input raster or constant value The input for which to calculate the inverse tangent values.To use a number as an input for this parameter, the cell size and extent must first be set in the environment. Raster Layer; Constant

### Return Value

 Label Explanation Data Type Output raster The output raster.The values are the inverse tangent of the input values. Raster

`ATan(in_raster_or_constant)`
 Name Explanation Data Type in_raster_or_constant The input for which to calculate the inverse tangent values.To use a number as an input for this parameter, the cell size and extent must first be set in the environment. Raster Layer; Constant

### Return Value

 Name Explanation Data Type out_raster The output raster.The values are the inverse tangent of the input values. Raster

### Code sample

ATan example 1 (Python window)

This example calculates the inverse tangent of the values in the input Grid raster.

``````import arcpy
from arcpy import env
from arcpy.ia import *
env.workspace = "C:/iapyexamples/data"
outATan = ATan("degs")
outATan.save("C:/iapyexamples/output/outatan")``````
ATan example 2 (stand-alone script)

This example calculates the inverse tangent of the values in the input Grid raster and outputs a TIFF raster.

``````# Name: ATan_Ex_02.py
# Description: Calculates the inverse tangent of pixels in a raster
# Requirements: Image Analyst Extension

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

# Set environment settings
env.workspace = "C:/iapyexamples/data"

# Set local variables
inRaster = "degs"

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

# Execute ATan
outATan = ATan(inRaster)

# Save the output
outATan.save("C:/iapyexamples/output/outatan.tif")``````

## Licensing information

• Basic: Requires Image Analyst or Spatial Analyst
• Standard: Requires Image Analyst or Spatial Analyst
• Advanced: Requires Image Analyst or Spatial Analyst