g.gui.gcp(1)

📦
version 8.4.2 · 10 versions
, in fedora 44

🎀 g.gui.gcp 🎀

okay so this is the GRASS GIS User's Manual page for g.gui.gcp, and bestie, it's giving ground control points but make it a whole GUI. Pull up a chair. 🫶

✨ NAME ✨

g.gui.gcp — georectifies a map and allows managing Ground Control Points. That's it, that's the job. 💅

🌸 KEYWORDS 🌸

general, GUI, georectification, geometry, GCP

🦋 SYNOPSIS 🦋

g.gui.gcp
g.gui.gcp --help
g.gui.gcp  [--help]  [--verbose]  [--quiet]  [--ui]

⭐ Flags ⭐

  • --help — prints a usage summary, i.e. the "what even is this" button 🙈
  • --verbose — verbose module output, she's chatty, we love her 💬
  • --quiet — quiet module output, she's mysterious, we also love her 🤫
  • --ui — forces the GUI dialog to launch. no cap, it's gonna pop off 🪟

👑 DESCRIPTION 👑

The GCP Manager is a wxGUI extension, and what it does is let you create, edit, and manage Ground Control Points. You can find it chilling in the menu under "File | Manage Ground Control Points". slay.

The GCP Manager hands you an interactive graphical interface to manage and analyze Ground Control Points. Here's the iconic part: a backup copy of the initial POINTS file is always maintained and it only gets updated on request (Save GCPs to POINTS file). Translation: accidental changes are never permanent, and you can undo the whole thing by reloading the Ground Control Points. we stan a safety net. 🛟

⚠️ The GCP Manager must be started in the target project, not in the source project. Not a drill, bestie. read that twice.

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 it with the caption, or by clicking the pin button on the right in the caption. It can also be placed below the map displays by dragging. she's flexible like that 💅
  • The two panels in the lower part are 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 show up on both map displays. matching fits, main character energy ✨

🧚 Components of the GCP Manager 🧚

🛠️ Toolbars

Two toolbars come with the GCP Manager: one for managing the map displays, and one for managing the GCP list. two icons, two moods.

📋 List of ground control points

The list of Ground Control Points can be sorted by clicking on a column header. Click a column header once → GCPs sort ascending. Click the same column a second time → they sort descending. 🔃

Real talk: overall RMS error and individual RMS errors of all points often get better if you adjust the GCP with the highest RMS error. And you can edit individual coordinates by double-clicking on a row. easy.

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 it to deactivate a GCP (mark as unused GCP). it's the on/off switch of destiny ✅

🗺️ Two panels for map display

Left panel = a map from the source project. Right panel = 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. no shared zoom, they're independent queens 💫

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 at all. bye felicia 🎨

📊 Statusbar

At the bottom of the GCP Manager there's a statusbar doing several jobs. Default is set to Go to GCP No. (more on that below). Type a number, or use the up/down arrows, and it will center the maps on that given GCP — extremely useful when you're zoomed way in. 🔍

🔥 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. she checks what changed, she's efficient 💅
  • Re-render map — re-renders both source and target canvas regardless of whether they have changed or not. no thoughts, just redraw 🔄
  • Erase display — erases both source and target canvas to a white background. clean slate, blank canvas, fresh start 🤍
  • Define GCP (Ground Control Points) — on left mouse click, coordinates are defined for the currently selected GCP. click, and it's canon 📍
  • 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. just sliding around, no resizing 🖐️
  • 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). closer, bestie 🔎
  • 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). back up, we're too close 😭
  • 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. choose your fighter 🎯
    • Return to previous zoom — returns to the previous zoom extent. Up to 10 levels of zoom back are maintained. the undo button of zooms ↩️
    • Zoom to extent of currently displayed map — zoom to the extent of the currently displayed map in the active map canvas (source or target). fit it all in frame 📐
  • 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. one point, one spotlight ✨
  • 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. two birds, one order 🐦
  • 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.

And then:

  • Show Help — show the help page for the GCP Manager. 📖
  • Quit — quit the GCP Manager. say bye 👋

💜 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. double protection, double slay 💾
  • Add new GCP — adds a new Ground Control Point to the list and selects it for editing. new baby just dropped 👶
  • Delete selected GCP — deletes the currently selected GCP from the list. gone, reduced to atoms 💀
  • Clear selected GCP — resets all coordinates of the currently selected GCP to 0 (zero). not deleted, just zeroed, big difference 🫧
  • Reload GCPs from POINTS file — reloads GCPs from the imagery group's POINTS file. the undo, the reset, the "nvm" button 🔁
  • 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. the finale 🎆

📍 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. glow-up, honestly ✨

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. the numbers, she speaks 📈

🫶 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)

Accessed: Saturday Jan 17 05:42:35 2026

Main index | GUI index | Topics index | Keywords index | Graphical index | Full index

💖 and that's the whole page bestie. shoutout to the source: © 2003-2025 GRASS Development Team, GRASS GIS 8.4.2 Reference Manual — this is GRASS 8.4.2, page g.gui.gcp(1), accessed on Saturday Jan 17 05:42:35 2026. go georectify something iconic. periodt. 💅✨
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