The GCPManager is a wxGUI extension which allows the user to create, edit, and manage Ground Control
Points. It is available from the menu "File | Manage Ground Control Points".
The GCPManager provides an interactive graphical interface to manage and analyze Ground Control Points.
A backup copy of the initial POINTS file is always maintained and updated only on request (Save GCPs to
POINTS file). This guarantees that accidental changes are not permanent and can be undone by reloading
the Ground Control Points.
The GCP Manager must be started in the target project, not in the source project (project used to be
called location).
The GCP Manager is structured into three panels:
• The topmost panel shows a list of Ground Control Points. Tools to manipulate and analyze GCPs are
provided in the toolbar. This panel can be moved out of the GCP manager window by either dragging
with the caption or by clicking on the pin button on the right in the caption. This panel can
also be placed below the map displays by dragging.
• The two panels in the lower part are used for map and GCP display, the left pane showing a map
from the source project and the right pane showing a reference map from the target project.
Numbered Ground Control Points are shown on both map displays.
ComponentsoftheGCPManagerToolbars
Two toolbars are provided with the GCP Manager, one for managing the map displays and one for managing
the GCP list.
Listofgroundcontrolpoints
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).
Twopanelsformapdisplay
The left panel is used to display a map from the source project, the right panel to display a map from
the target project. 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 GotoGCPNo. (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.
GCPMapDisplayToolbarDisplaymap
Displays maps for source and target canvas and re-renders any layers that have changed since the last
time the display was updated.
Re-rendermap
Re-renders both source and target canvas regardless of whether they have changed or not.
Erasedisplay
Erases both source and target canvas to a white background.
DefineGCP(GroundControlPoints)
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.
Zoomin
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).
Zoomout
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).
Adjustdisplayzoom
Source and target display are adjusted by using the current GCPs for coordinate transformation:
Adjustsourcedisplaytotargetdisplay
The extents of the source display are adjusted to the current extents of the target display.
Adjusttargetdisplaytosourcedisplay
The extents of the source display are adjusted to the current extents of the target display.
Setactivemapcanvas
Sets the currently active map canvas (source or target). Click to set active map canvas for Returntopreviouszoom or Zoomtoextentofcurrentlydisplayedmap. Alternatively, move the mouse over the
map canvas to be used as active canvas.
Returntopreviouszoom
Returns to the previous zoom extent. Up to 10 levels of zoom back are maintained.
Zoomtoextentofcurrentlydisplayedmap
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:
HighlighthighestRMSerroronly
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.
FactorforRMSerrorthreshold=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 HighlighthighestRMSerroronly is unchecked.
Color
Set the color for GCPs on the GCP Map Display.
ColorforhighRMSerror
Set the color for GCPs with a high RMS error on the GCP Map Display.
ColorforselectedGCP
Set the color for the currently selected GCP on the GCP Map Display.
ShowunusedGCPs
If unchecked, unused GCPs will not be shown on the GCP Map Display.
ColorforunusedGCPs
Set the color for unused GCPs on the GCP Map Display.
Symbolsize
Set the symbol size for GCPs on the GCP Map Display.
Linewidth
Set the line width for GCPs on the GCP Map Display.
Selectsourcemaptodisplay
Select a source map for the left pane of the GCP Map Display.
Selecttargetmaptodisplay
Select a target map for the right pane of the GCP Map Display.
Rectification
Settings for georectification:
Selectrectificationmethod
Set the polynomial order for georectification. This order will also be used for RMS error
calculation.
Cliptocomputationalregionintargetproject
Clip raster maps to the current computational region in the target project when georectifying.
Extensionforoutputmaps
Change the extension for output map names when doing the actual georectification.
ShowHelp
Show help page for the GCP Manager.
Quit
Quit the GCP Manager.
ToolbarfortheGCPlistSaveGCPstoPOINTSfile
The current list of GCPs is saved to the imagery group’s POINTS file and to a backup copy.
AddnewGCP
Adds a new Ground Control Point to the list and selects it for editing.
DeleteselectedGCP
Deletes the currently selected GCP from the list.
ClearselectedGCP
Resets all coordinates of the currently selected GCP to 0 (zero).
ReloadGCPsfromPOINTSfile
Reloads GCPs from the imagery group’s POINTS file.
RecalculateRMSerror
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.
GCPMapDisplayStatusbar
The GCP map display statusbar is similar to the statusbar in the regular GRASS GIS map display with two
differences, Goto has been replaced with GotoGCPNo. and Projection has been replaced with RMSerror.
If GotoGCPNo. 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 RMSerror is selected, the overall forward and backward RMS error is displayed.
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