Documentation | Help File | UI | 2D Mode | Menu | Layer | Rectify | Rectification window

The Rectification window is invoked upon clicking on the OK button in the Options dialog dialog box, following the opening of a layer without a recognized coordinate system.

Rectification window. An aerial image (left map area) to be rectified using GCP points taken from a vector map reference layer (right map area). Information for each GCP point is visible in GCP table.

The Rectification window provides tools to apply GCP (Ground Control Point) (GCPs) to the working map layer (the layer to be rectified), from which the rectification transformation is performed. Based on GCP placements, the Rectification process rotates, scales, and georeferences a vector map or raster (image, grid) layer to a coordinate system. If the layer contains distortions, the 2nd and 3rd order rectification calculations can also skew and Warp the layer to correct the distortions and transform the coverage to the integrity of a map. Rrectification requires that a minimum number of GCPs be accurately applied to the working layer: 3 GCPs for the 1st order transformation method, 6 GCPs for the 2nd order transformation method, and 10 GCPs for the 3rd order transformation method. GCPs can be applied to the working layer by i) entering the GCP coordinates from the keyboard or ii) lifting GCPs from a reference layer.

If a referenced layer is selected in the Rectification options dialog box, the reference layer automatically opens in the right map area (see the above image). The program automatically reads the coordinate system information of the reference layer. The rectified output can be generated to the reference layer coordinate system or to any other other coordinate system selected in the Rectification options dialog box.

The rectification transformation information is saved to a TRN file file (with the same name as the working layer file, but with the *.TRN extension) and the rectification coordinate system to a PRJ file (with the same name as the working layer file, but with the *.PRJ extension), both to the same folder as working the layer file. The working layer file is not changed in any way (no changes are saved to the layer file) and no new layer is created. Any time the rectified layer is subsequently opened in the Editor or other TatukGIS product, the software uses the information in the associated TRN and PRJ files to instantaneously (on-the-fly) transform the layer display to the rectified result. (Therefore, deleting the TRN file for a layer will clear the rectification transformation.)

To save a rectification result without a TRN file (such as for use in a non-TatukGIS software program), export the rectified layer to a new vector or raster layer file. Because the export is performed post-rectification, the newly created layer inherently reflects the rectification transformation (without need for a TRN file and on-the-fly transformation). Use Export function to export a vector layer and Export to image function to export an image layer.

Procedure to apply GCP points

If using a reference layer, use the Add point tool (Select mode must be active) with the mouse cursor to identify (by clicking) a GCP location on the reference layer (right map area) and then click with the mouse on exactly the same map location on the working layer (left map area). Zoom and scroll on the working and reference layers as required. The GCP and coordinates will appear in the GCP table at the bottom of the Rectification window. If not using a reference layer, use the Add point tool with the mouse cursor to identify a GCP location on the working layer (alternatively, use Select mode and the Edit tool to drag an existing GCP on the working layer to the correct position) and then use the keyboard to enter the coordinates for the GCP in the To X (Long) and To Y (Lat) columns in the GCP table. Repeat this procedure to add at least the minimum number of GCPs required by the rectification method.

GCP coordinates can be edited and turned on (active) or off (inactive) within the GCP table. When in Active mode and enough GCPs are applied, the rectification result is instantaneously (on-the-fly) recalculated to show the effect from each GCP related change.

The Toolbar provides quick access to the most frequently used rectification features.

Icon	Short description
Active	Active means on-the-fly layer rectification is turned on.  Use this option to turn on/off the on-the-fly rectification feature.
	Full exten t Select to change map view to full extent (fit whole extent of working or reference file into the map window).
	Reference layer extent Select to change map view to reference extent .
	Zoom mode Select to enter zooming mode on working or reference map (or rotate the mouse wheel). Zoom-in by dragging mouse cursor on map in right-down direction. Zoom-out by dragging mouse cursor on map in left-up direction.
	Drag mode Select to enter dragging (panning) mode on working or reference map. Dragging mouse cursor moves entire map within the window.
	Select mode Select to enter selection mode on working map (left map window). Click with left mouse button to select features on working map layer. GCPs or the Bounding polygon may be selected for editing.
	Bounding polygon Select to enter bounding polygon edit mode. Select again to exit bounding polygon edit mode. Use to remove unwanted border areas of the working file coverage from the rectification process or  otherwise specify only a portion of the working file coverage for rectification. User can reset the bounding polygon in the Reset dialog
	Edit mode Use to edit the location or coordinates of the selected GCP or to edit the bounding polygon. Edit mode becomes active when a GCP is selected (on the map or within the GCP panel) using select mode ( icon) or when bounding polygon editing mode ( icon) is active.
	Add point Select to add a new GCP point. This feature becomes active when in select mode ( icon)
	Delete selected point Use to delete the currently selected GCP point. This feature is active only when a GCP point is selected.
	Zoom to point Select to zoom in to the currently selected GCP point.
	Flash point Select to flash the currently selected GCP point.
	Display all Select to display all data - map layers, GCP points, and RMS errors of each GCP) in working and reference map windows.
	Display points Select to display only GCP points in working and reference map windows. Map layers are hidden.
	Display layers Select to display only the map layers in working and reference map windows. GCP points are hidden.
	Show errors Select to turn on/off the RMS error display in working map window. Errors are shown as red circles - the larger the circle, the larger the error.
	Undo (edit) Select to undo the previous GCP point movement.
	Redo (edit) Select to redo the previous GCP point movement.
Reset…	Opens the Rectification reset dialog box, which is used to reset bounding polygon or GCP points to default settings.
Options…	Opens the Rectification options dialog box, which contains the main rectification settings and options.

GCP table

To select an existing GCP point

• Select point: click on the select mode icon and then click on the GCP, either on the map or within the GCP table.

This table is used to enter or edit x, y coordinates for each GCP (Ground Control Point) point. The coordinate data for each GCP can be entered manually from the keyboard, or lifted from a reference layer opened in the reference map window using the mouse cursor. Any georeferenced aerial image, raster map image, or vector map can be used as the reference layer (provided the coverage overlaps the map area of the working file).

GCP table columns

• As with the Open function, the program automatically reads the coordinate system of a reference layer by checking for coordinate system information i) embedded natively in the layer and/or ii) contained in an external PRJ, World, TRN, and/or TAB registration file associated to the layer.
• If a layer without a recognized coordinate system (such as a scanned map, CAD drawing, etc.) is used as a reference layer, the program uses the coordinate system of the pixels (left-upper most pixel has coordinates 0,0, and so on), or other coordinate system information contained in the reference layer, to perform the rectification job. This enables rectifying/georeferencing a layer to match the coordinate space of any reference layer, even when that coordinate system is unrecognized (unknown).
• The format for the GCP coordinates (decimal units or degrees/minutes/seconds) can be specified within the Options dialog dialog which is opened by clicking on the Options button. The degree/minute/second option is not available when using a coordinate system with a projection that does not use degrees.