wxGUI.image2target(1)

📦

version 8.4.2 · 10 versions

✨ wxGUI GCP Manager ✨

okay so bestie, you opened wxGUI.image2target(1) and you're like "what is this" — and honestly? it's the GCP Manager, a wxGUI extension that lets you create, edit, and manage Ground Control Points like the icon you are. 💅 You get to it from the menu "File | Manage Ground Control Points".

🎀 DESCRIPTION 🎀

The GCP Manager is a whole vibe: it gives you an interactive graphical interface to manage and analyze Ground Control Points. And here's the part that matters — a backup copy of the initial POINTS file is always maintained and only updated when you explicitly ask (that's the Save GCPs to POINTS file action). So accidental changes are never permanent, and you can undo them by just reloading the Ground Control Points. slay. 🫶

Heads up bestie: the GCP Manager must be started in the target project, NOT the source project. (a project used to be called a location, iykyk)

The GCP Manager is structured into three panels:

The topmost panel shows a list of Ground Control Points. Tools to manipulate and analyze GCPs live in the toolbar. This panel can be moved out of the GCP manager window either by dragging with the caption or by clicking on the pin button on the right in the caption. It can also be placed below the map displays by dragging. very flexible of her.
The two panels in the lower part are used for map and GCP display: the left pane shows a map from the source project, the right pane shows a reference map from the target project. Numbered Ground Control Points are shown on both map displays. 🌈

🛠️ Components of the GCP Manager

Toolbars

Two toolbars are provided with the GCP Manager, bestie: one for managing the map displays and one for managing the GCP list. one for the maps, one for the list. iconic duo fr.

📋 List of ground control points

The list of Ground Control Points can be sorted by clicking on a column header. Clicking on a column header will sort the GCPs ascending; a second click on the same column will sort them 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 project, the right panel to display a map from the target project. Zooming in and out is always possible with the mouse wheel, and it's 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 — super useful with a high zoom. ✨

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 the 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 project — Clip raster maps to the current computational region in the target project 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.

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

💖 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)

Accessed: Saturday Jan 17 05:42:36 2026

© 2003-2025 GRASS Development Team, GRASS GIS 8.4.2 Reference Manual

okay that's the whole thing bestie, you ate. this page is from GRASS 8.4.2, last accessed Saturday Jan 17 05:42:36 2026, and it's wxGUI.image2target(1) — go make some Ground Control Points, main character. 💅✨🦋

📦 where this page comes from

fedora 44: grass 8.4.2-4.fc44 · GPL-2.0-or-later
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on 2026-10-18: a language model's rewrite of the original, under its terms