guide:help:rctrectifyoptions

Documentation | Help File | UI | 2D Mode | Menu | Layer | Rectify | ** Options dialog **

The `Rectification options`

dialog box is invoked when the user selects the `Rectify`

option in the Rectify Layer warning message box after opening a layer with an unrecognized coordinate system. This dialog box can also be accessed from the Rectification window by clicking on the `Options`

button in that panel. Additionally the `Rectification options`

dialog box can be opened for any active layer (the highlighted layer in the Legend) by clicking on menu item Rectify.

The `Rectification options`

dialog box provides settings to control the rectification transformation, e.g. coordinate system, rectification method, whether to use a reference layer, etc.

The `Coordinate system`

option provides for setting the coordinate system for the layer being rectified i.e. the coordinate system for the rectification output. Clicking on the `…`

button to the right of the `Coordinate system`

option opens the `Coordinate system`

dialog box containing thousands of predefined coordinate systems. The predefined coordinate systems are organized into two drop-down lists: `Projected systems`

reflecting linear distance units (meters, feet, kilometers, miles…) and `Geographic systems`

reflecting angular units (degrees, radians, or grads).

If manual coordinate system definition is required (such as to define a coordinate system that is not predefined, clicking on the `…`

button to the right of the `Projected system`

list or to the right of the `Geographic system`

list opens the `Coordinate System Setup`

dialog box with hundreds of projections, datums, units, and other settings to custom define a projected or geographic coordinate system. Refer to the Coordinate Systems help topic for guidance on setting a coordinate system.

When a layer without coordinate system information is opened the first time, the coordinate system is displayed as `UNKNOWN`

in the `Rectification options`

dialog box. The user can open the `Coordinate System`

dialog to select or define the coordinate system or use a reference layer and apply the coordinate system of the reference layer.

- If the
`Coordinate system`

setting is left as`UNKNOWN`

and a reference layer is used, the program will apply the coordinate system of the reference layer when the`Rectification options`

dialog is closed (performed by clicking on the`OK`

button). - If the
`Coordinate system`

setting is left as`UNKNOWN`

and a no reference layer is selected, the program will apply, by default, the`WGS84`

coordinate system when the`Rectification options`

dialog is closed. - If the user manually selects or defines a coordinate system in the
`Coordinate system`

dialog, the coordinate system selection will not be overridden by the reference layer coordinate system (if a reference layer is used) when the`Rectification options`

dialog is closed. - If
`Layer/Rectify`

menu item is used to open the`Rectification options`

dialog box for the active layer with coordinate system, the`Coordinate system`

selection in the dialog box is auto-filled by the layer's coordinate system (which the user can change if desired).

The `Rectification method`

setting enables selection of the rectification method, with a choice between the 1st, 2nd or 3rd order polynomial transformations (also commonly referred to as the Rectification - Polynomial Transformation Method method of transformation). The degree of complexity of the polynomial equation is expressed as the order of the polynomial used for the transformation. All three methods rotate, scale, and georeference the layer to a coordinate system. When layer distortion is detected, the 2nd and 3rd order transformation methods also apply warping to correct correct the distortion. The higher the order, the more complex the polynomial equation and the greater the level of distortion that can be corrected by the warping.

The 1st order transformation is a linear transformation which rotates and Scale the image or vector coverage. This corrects the types of distortion that would be evident even if the terrain is a flat plane, like the surface of a table, in which the distortion is systematic across the entire coverage. The 1st order transformation can be appropriate, for example, to georeference scanned raster maps or to rectify and georeference aerial images of relatively smaller ground areas of flat terrain (in which the curvature of the earth is not a significant factor).

The 2nd and 3rd orders of transformation are nonlinear transformations which can correct more complex distortions in a coverage. The 2nd order transformation, for example, might be effective to correct the relatively systematic distortions in a satellite image caused by the curvature of the earth relative to the camera position or to correct the irregular scaling of images of relatively larger ground areas. The 3rd order transformation might be used to correct more complex distortion caused, for example, by elevation variations of the terrain (hills) relative to the camera angle. The most appropriate rectification method for a given situation is a matter of judgment.

The `Coordinates format`

setting enables selection of the units format - decimal units or degrees/minutes/seconds - for entering GCP coordinates and presentation of the coordinates in the GCP table. The degree/minute/second option is not available when using a coordinate system with a projection that does not use degrees.

The `Reference file`

option enables using a georeferenced vector map, scanned map, or aerial image coverage as a reference layer. (The reference layer opens in the right map area of the `Rectification`

window). This enables taking GCP points directly from the reference layer using the mouse cursor, which is intuitive and avoids manually entering GCP coordinates from the keyboard.

- TatukGIS coordinate system naming reflects OpenGIS (OGC) WKT definitions and EPSG codes.

2018/05/17 16:00