Components of the GCP Manager

Toolbars

Two toolbars are provided with the GCP Manager, one for managing the map displays and one for managing the GCP list.

List of ground control points

The list of Ground Control Points can be sorted by clicking on a column header. Clicking on a cloumn header will sort the GCPs ascending, a second click on the same column will sort the GCPs descending. Overall RMS error and individual RMS errors of all points are often improved if the GCP with the highest RMS error is adjusted. Individual coordinates can be edited by double-clicking on a row.

The first column holds a checkbox and displays the point number. A GCP is only used for RMS error calculation and georectification if its checkbox on the left is checked. Uncheck to deactivate a GCP (mark as unused GCP).

Two panels for map display

The left panel is used to display a map from the source location, the right panel to display a map from the target location. Zooming in and out is always possible with the mouse wheel and done for each map canvas separately.

GCPs are displayed in different colors, depending on whether a GCP has a high RMS error, is currently unused or is currently selected. Optionally, currently unused GCPs are not shown on the map display.

Statusbar

At the bottom of the GCP Manager is a statusbar providing several functions. The default is set to Go to GCP No. (see also below). Typing a number or using the up/down arrows will center the maps on the given GCP, useful with a high zoom.

GCP Map Display Toolbar

  Display map

Displays maps for source and target canvas and re-renders any layers that have changed since the last time the display was updated.

  Re-render map

Re-renders both source and target canvas regardless of whether they have changed or not.

  Erase display

Erases both source and target canvas to a white background.

  Define GCP (Ground Control Points)

On left mouse click, coordinates are defined for the currently selected GCP.

  Pan

Interactive selection of a new center of view in the active display monitor. Drag the pan cursor while pressing the left mouse button to pan. Alternatively left-click on the new center. Panning changes the location of the region displayed but not the size of the area displayed or the resolution.

  Zoom in

Interactive zooming with the mouse in the active map canvas (source or target). Drawing a box or just a left click with the mouse and zoom-in cursor causes the display to zoom in so that the area defined by the box fills the display. The map resolution is not changed. Clicking with the zoom-in cursor causes the display to zoom in by 30%, centered on the point where the mouse is clicked. Zooming changes the display region extents (both size and location of area displayed).

  Zoom out

Interactive zooming with the mouse in the active map canvas (source or target). Drawing a box or just a left click with the mouse and zoom-out cursor causes the display to zoom out so that the area displayed shrinks to fill the area defined by the box. The map resolution is not changed. Clicking with the zoom-out cursor causes the display to zoom out by 30%, centered on the point where the mouse is clicked. Zooming changes the display region extents (both size and location of area displayed).

  Adjust display zoom

Source and target display are adjusted by using the current GCPs for coordinate transformation:

Adjust source display to target display

The extents of the source display are adjusted to the current extents of the target display.

Adjust target display to source display

The extents of the source display are adjusted to the current extents of the target display.

Set active map canvas

Sets the currently active map canvas (source or target). Click to set active map canvas for Return to previous zoom or Zoom to extent of currently displayed map. Alternatively, move the mouse over the map canvas to be used as active canvas.

  Return to previous zoom

Returns to the previous zoom extent. Up to 10 levels of zoom back are maintained.

  Zoom to extent of currently displayed map

Zoom to the extent of the currently displayed map in the active map canvas (source or target).

  Settings

Shows a settings dialog for GCP management and display:

Symbology

Settings for map and GCP display:

Highlight highest RMS error only

Only the GCP with the highest RMS error will be displayed in a different colour, both in the list of GCPs and the GCP Map Display.

Factor for RMS error threshold = M + SD * factor:

All GCPs with an RMS error larger than mean RMS + RMS standard deviation * this factor will be displayed in a different colour, both in the list of GCPs and the GCP Map Display. As a rule of thumb, GCPs with an RMS error larger than M + SD * 2 are most probably wrong. GCPs with an RMS error larger than M + SD * 1 are worth closer inspection. This option is only available if Highlight highest RMS error only is unchecked.

Color

Set the color for GCPs on the GCP Map Display.

Color for high RMS error

Set the color for GCPs with a high RMS error on the GCP Map Display.

Color for selected GCP

Set the color for the currently selected GCP on the GCP Map Display.

Show unused GCPs

If unchecked, unused GCPs will not be shown on the GCP Map Display.

Color for unused GCPs

Set the color for unused GCPs on the GCP Map Display.

Symbol size

Set the symbol size for GCPs on the GCP Map Display.

Line width

Set the line width for GCPs on the GCP Map Display.

Select source map to display

Select a source map for the left pane of the GCP Map Display.

Select target map to display

Select a target map for the right pane of the GCP Map Display.

Rectification

Settings for georectification:

Select rectification method

Set the polynomial order for georectification. This order will also be used for RMS error calculation.

Clip to computational region in target location

Clip raster maps to the current computational region in the target location when georectifying.

Extension for output maps

Change the extension for output map names when doing the actual georectification.

  Show Help

Show help page for the GCP Manager.

  Quit

Quit the GCP Manager.

Toolbar for the GCP list

  Save GCPs to POINTS file

The current list of GCPs is saved to the imagery group’s POINTS file and to a backup copy.

  Add new GCP

Adds a new Ground Control Point to the list and selects it for editing.

  Delete selected GCP

Deletes the currently selected GCP from the list.

  Clear selected GCP

Resets all coordinates of the currently selected GCP to 0 (zero).

  Reload GCPs from POINTS file

Reloads GCPs from the imagery group’s POINTS file.

  Recalculate RMS error

Recalculates forward and backward RMS error for all GCP marked for use (activated checkbox in first row).

  Georectify

Uses i.rectify to georectify all images in the source imagery group.

GCP Map Display Statusbar

The GCP map display statusbar is similar to the statusbar in the regular GRASS GIS map display with two differences, Go to has been replaced with Go to GCP No. and Projection has been replaced with RMS error.

If Go to GCP No. is selected, a GCP number can be given in the left side of the statusbar and the source and target map canvas will be centered on the given GCP. Clicking on the map canvas will update coordinates for this GCP.

If RMS error is selected, the overall forward and backward RMS error is displayed.