## Summary

Transforms a raster dataset using source and target control points. This is similar to georeferencing.

## Illustration

## Usage

You must specify the source and target coordinates. The transformation type (polynomial order) from which to choose is dependent on the number of control points entered.

The default polynomial order will perform an affine transformation.

Warp is useful when the raster requires a systematic geometric correction that can be modeled with a polynomial. A spatial transformation can invert or remove a distortion by using polynomial transformation of the proper order. The higher the order, the more complex the distortion that can be corrected. The higher orders of polynomial will involve progressively more processing time.

To determine the minimum number of links necessary for a given order of polynomial, use the following formula:

`n = (p + 1) (p + 2) / 2`

where n is the minimum number of links required for a transformation of polynomial order p. It is strongly suggested to use more than the minimum number of links.

This tool will determine the extent of the warped raster and will set the number of rows and columns to be about the same as in the input raster. Some minor differences may be due to the changed proportion between the output raster's sizes in the x and y directions. The default cell size used will be computed by dividing the extent by the previously determined number of rows and columns. The value of the cell size will be used by the resampling algorithm.

If you choose to define an output cell size in the Environment Settings, the number of rows and columns will be calculated as follows:

`columns = (xmax - xmin) / cell size rows = (ymax - ymin) / cell size`

You can save your output to BIL, BIP, BMP, BSQ, DAT, Esri Grid , GIF, IMG, JPEG, JPEG 2000, PNG, TIFF, or any geodatabase raster dataset.

When storing your raster dataset to a JPEG file, a JPEG 2000 file, or a geodatabase, you can specify a Compression Type and Compression Quality in the Environments.

## Syntax

Warp_management (in_raster, source_control_points, target_control_points, out_raster, {transformation_type}, {resampling_type})

Parameter | Explanation | Data Type |

in_raster | The raster that you want to transform. | Mosaic Layer; Raster Layer |

source_control_points [source_control_point,...] | The source points are the coordinates of the raster that you are trying to warp. | Point |

target_control_points [target_control_point,...] | The target points are the coordinates where you want the source raster to be warped to. | Point |

out_raster | Specify a name, location and format for the dataset you are creating. When storing a raster dataset in a geodatabase, do not add a file extension to the name of the raster dataset. When storing your raster dataset to a JPEG file, a JPEG 2000 file, a TIFF file, or a geodatabase, you can specify a compression type and compression quality. When storing the raster dataset in a file format, you need to specify the file extension: - .bil—Esri BIL
- .bip—Esri BIP
- .bmp—BMP
- .bsq—Esri BSQ
- .dat—ENVI DAT
- .gif—GIF
- .img—ERDAS IMAGINE
- .jpg—JPEG
- .jp2—JPEG 2000
- .png—PNG
- .tif—TIFF
- No extension for Esri Grid
| Raster Dataset |

transformation_type (Optional) | Select a method for shifting the raster dataset. - POLYORDER0 — This method uses a zero-order polynomial to shift your data. This is commonly used when your data is already georeferenced, but a small shift will better line up your data. Only one link is required to perform a zero-order polynomial shift.
- POLYSIMILARITY — This is a first order transformation that attempts to preserve the shape of the original raster. The RMS error tends to be higher than other polynomial transformations because the preservation of shape is more important than the best fit.
- POLYORDER1 —A first-order polynomial (affine) fits a flat plane to the input points.
- POLYORDER2 —A second-order polynomial fits a somewhat more complicated surface to the input points.
- POLYORDER3 —A third-order polynomial fits a more complicated surface to the input points.
- ADJUST — This method combines a polynomial transformation and uses a triangulated irregular network (TIN) interpolation technique to optimize for both global and local accuracy.
- SPLINE — This method transforms the source control points precisely to the target control points. In the output, the control points will be accurate, but the raster pixels between the control points are not.
- PROJECTIVE — This method warps lines so they remain straight. In doing so, lines that were once parallel may no longer remain parallel. The projective transformation is especially useful for oblique imagery, scanned maps, and for some imagery products.
| String |

resampling_type (Optional) | The resampling algorithm to be used. The default is Nearest. - NEAREST — Nearest neighbor is the fastest resampling method; it minimizes changes to pixel values since no new values are created. It is suitable for discrete data, such as land cover.
- BILINEAR — Bilinear interpolation calculates the value of each pixel by averaging (weighted for distance) the values of the surrounding four pixels. It is suitable for continuous data.
- CUBIC — Cubic convolution calculates the value of each pixel by fitting a smooth curve based on the surrounding 16 pixels. This produces the smoothest image but can create values outside of the range found in the source data. It is suitable for continuous data.
- MAJORITY —Majority resampling determines the value of each pixel based on the most popular value in a 3 by 3 window. Suitable for discrete data.
The Nearest and Majority options are used for categorical data, such as a land-use classification. The Nearest option is the default since it is the quickest and also because it will not change the cell values. Do not use either of these for continuous data, such as elevation surfaces. The Bilinear option and the Cubic option are most appropriate for continuous data. It is recommended that neither of these be used with categorical data because the cell values may be altered. | String |

## Code sample

##### Warp example 1 (Python window)

This is a Python sample for the Warp tool.

```
import arcpy
from arcpy import env
env.workspace = "c:/data"
source_pnt = "'234718 3804287';'241037 3804297';'244193 3801275'"
target_pnt = "'246207 3820084';'270620 3824967';'302634 3816147'"
arcpy.Warp_management("raster.img", source_pnt, target_pnt, "warp.tif", "POLYORDER1",\
"BILINEAR")
```

##### Warp example 2 (stand-alone script)

This is a Python script sample for the Warp tool.

```
##====================================
##Warp
##Usage: Warp_management in_raster source_control_points;source_control_points...
## target_control_points;target_control_points... out_raster
## {POLYORDER_ZERO | POLYORDER1 | POLYORDER2 | POLYORDER3 |
## ADJUST | SPLINE | PROJECTIVE} {NEAREST | BILINEAR |
## CUBIC | MAJORITY}
import arcpy
arcpy.env.workspace = r"C:/Workspace"
##Warp a TIFF raster dataset with control points
##Define source control points
source_pnt = "'234718 3804287';'241037 3804297';'244193 3801275'"
##Define target control points
target_pnt = outpnts = "'246207 3820084';'270620 3824967';'302634 3816147'"
arcpy.Warp_management("raster.img", source_pnt, target_pnt, "warp.tif", "POLYORDER2",\
"BILINEAR")
```

## Environments

## Licensing information

- ArcGIS Desktop Basic: Yes
- ArcGIS Desktop Standard: Yes
- ArcGIS Desktop Advanced: Yes