# ATan (Spatial Analyst)

## Summary

Calculates the inverse tangent of cells in a raster.

## Illustration

 OutRas = ATan(InRas)

## 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 Domain is : -∞ < [in_value] < ∞

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

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

• The input values to ATan 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. If degrees are desired, the resulting raster must be multiplied by the radians-to-degrees conversion factor of 180/pi, or approximately 57.296.

See here for examples of converting output values from radians to degrees.

## Syntax

ATan (in_raster_or_constant)
 Parameter Explanation Data Type in_raster_or_constant The input for which to calculate the inverse tangent values. In order 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.sa import *
env.workspace = "C:/sapyexamples/data"
outATan = ATan("degs")
outATan.save("C:/sapyexamples/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 cells in a raster
# 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 = "degs"

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

# Execute ATan
outATan = ATan(inRaster)

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

## Licensing Information

ArcView: Requires Spatial Analyst
ArcEditor: Requires Spatial Analyst
ArcInfo: Requires Spatial Analyst

6/29/2011