Provided by: grass-doc_7.8.2-1build3_all 
wxGUI GCP Manager
DESCRIPTION
The GCP Manager 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 GCP Manager 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 location, not in the source 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 location and the right pane showing a reference map
from the target location. Numbered Ground Control Points are shown on both map
displays.
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 loaction. 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.
SEE ALSO
wxGUI
wxGUI components
i.rectify, m.transform, v.rectify
See also video tutorials on GRASS Wiki.
AUTHORS
Markus Metz
Based on the Georectifier (GRASS 6.4.0) by Michael Barton
Martin Landa, Czech Technical University in Prague, Czech Republic
SOURCE CODE
Available at: wxGUI GCP Manager source code (history)
Main index | GUI index | Topics index | Keywords index | Graphical index | Full index
© 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual