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 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.
Toolbar provides quick access to the most frequently used rectification features.
|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 .
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.
Select to enter dragging (panning) mode on working or reference map.
Dragging mouse cursor moves entire map within the window.
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.
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
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.
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.
Select to flash the currently selected GCP point.
Select to display all data - map layers, GCP points, and RMS errors of each GCP) in working and reference map windows.
Select to display only GCP points in working and reference map windows. Map layers are hidden.
Select to display only the map layers in working and reference map windows. GCP points are hidden.
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.
Select to undo the previous GCP point movement.
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.|
To select an existing GCP point
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
|Active||Uncheck this box to make the GCP inactive. This feature enables removing a GCP(s) from the rectification calculation without deleting the GCP(s) and its coordinates. The GCP(s) can be reactivated by rechecking this box. In this way, the user can easily experiment with the effect of specific GCP(s) on the RMS error and rectification output, without deleting the GCP and its coordinates. The effect of such changes on the rectified output and RMS error values is instantaneously visible.|
|From X||X coordinate from the working file for the GCP location. The If the working file is not georeferenced, this information is meaningless. It can be considered as the X coordinate of the starting point.|
|From Y||Y coordinate from the working file for the GCP location. If the working file is not georeferenced, this information is meaningless. It can be considered as the Y coordinate of the starting point.|
|To X||X coordinate (longitude) of the GCP point (reflecting the rectification job coordinate system). It can be considered as the X coordinate of the target point.|
|To Y||Y coordinate (latitude) of the GCP point (reflecting the rectification job coordinate system). It can be considered as the Y coordinate of the target point.|
|RMS||Root Mean Square (RMS) error is the distance, in terms pixel widths (for image coverages) between the location defined by the GCP coordinates and the location that this pixel of the image (the pixel to which the GCP is assigned) will be transformed to in the rectified output. RMS error is calculated in a similar way for vector coverages. The RMS value for the average of all active GCPs taken together, and for any single selected GCP, are calculated on a real-time basis and displayed in the status bar. The RMS value for a single selected GCP is enclosed in ( ). RMS values are presented any time the minimum number of active GCPs required to calculate the RMS have been applied to the coverage. Pre-calculation of the RMS error requires one additional GCP than the minimum number required to perform the rectification transformation. The magnitude of the RMS error reflects the i) accuracy of the GCP placements, ii) accuracy of the GCP coordinates, iii) level of distortion in the coverage, and iv) order of the polynomial equation used for the rectification calculation.|
Optionsbutton. The degree/minute/second option is not available when using a coordinate system with a projection that does not use degrees.