### Register

This interface implements methods to register a raster. Image registration is establishment of correspondence between images of the same scene. Many image processing applications like remote sensing for change detection, estimation of wind speed and direction for weather forecasting, fusion of medical images need image registration. Image registration is a process of aligning two images acquired by same/different sensors, at different times or from different viewpoint.

To register images, we need to determine geometric transformation that aligns images with respect to the reference image. The most common transformations are:

- rigid (RST),

- affine,

- perspective.

The parameters of the geometric transformation are calculated based on a given set of tie-points.

The tie-points can be obtained manually or automatically as follows:

- Manual method: This is the case where the algorithm will generate the registered image based on manually selected tie-points,

- Automatic method: This is the case where tie-points are automatically generated by other algorithm comparing the input image with another reference image. The generated tie-points are later used by the register algorithm to generate the registered image.

It is accessible through:
Raster Processing > Register...

This wizard consists of the following steps:

#### Wizard Page 1 - Selection of the layer with the REFERENCE raster (Layer Search).

#### Wizard Page 2 - Selection of the layer with the ADJUST raster (Layer Search).

#### Wizard Page 3 - The register interface

The registration interface is composed of three components:

- In the red box shows the tools to control the tie points acquired. You can select and remove specific items. It also has a tool (wand) for automatic acquisition of the tie points.

- The first tool is a update button, used when the geometric parameters are changed.

- The user is allowed to add tie points from the definition of each coordinated via keyboard. At the bottom of this component are four fields that allows the user to set the values ​​for the coordinates. The (+) button inserts the values to the list of tie points.

- In the green box the user can define the parameters used for the execution of this operation. In the "Options" tab you can define specific parameters for each type of geometric transformation available *.

- In the orange box are presented displays containing the reference and adjust images so that the user can make the acquisition of the tie points (Raster Navigator).

* In the "General" tab, the following information is displayed:

- Reference Band: Band of reference image to be used in register operation.
- Adjust Band: Band of adjust image to be used in register operation.

- Input: Reference image metadata.

- SRID: Information about spatial reference system from image.
- Resolution X: horizontal resolution of the image pixels.
- Resolution Y: vertical resolution of the image pixels.

- Output: Adjust image metadata.

- SRID: Information about spatial reference system from image.
- Resolution X: horizontal resolution of the image pixels.
- Resolution Y: vertical resolution of the image pixels.

- Tie points number: Number of acquired tie points.

- Transformation RMSE: Calculates root mean square direct mapping error.

- All: For all tie points acquired.
- Selected: For selected tie points.
- Unselected: For unselected tie points.

In the "Options" tab are presented information about the geometric transformation:
Moravec options:

- Correlation Window Width: The correlation window width used to correlate points between the images (minimum 3, default: 11).

- Gaussian Filter Iterations: The number of noise Gaussian iterations, when applicable (used to remove image noise, zero will disable the Gaussian Filter, default:1).

- Minimum Correlation: The minimum acceptable absolute correlation value when matching features (when applicable), default:0.5, valid range: [0,1].

- Moravec Window Width: The Moravec window width used to locate candidate tie-points (minimum 3, default: 5 ).

Surf options:

- Maximum Euclidean Distance: The maximum acceptable euclidean distance when matching features (when applicable), default:0.5, valid range: [0,1].

- Octaves Number: The number of octaves to generate, when applicable (default: 3, minimum:1).

- Scales Number: The number of sub-sampling scales to generate, when applicable (default:4, minimum:3).

#### Wizard Page 4 - Output information (Output Raster Information).

Below is an example of using the registry interface, exploring the possible options.
Note that the color composite of the reference raster was changed to look something like to the adjustment raster.

- Example of manual acquisition of tie points:

- Example of automatic acquisition of tie points:

The result of this operation is shown in the figure below.