i.ortho.init(1)

📦
version 8.4.2 · 8 versions
, in fedora 44

💖 i.ortho.init 💖

okay bestie, welcome to i.ortho.init(1) from the GRASS GIS User's Manual — it's the little menu-based gremlin that writes your camera's starting position into a file so the ortho-rectification math has somewhere to begin. imagery, orthorectify. iykyk. 🎀

✨ NAME ✨

i.ortho.init — creates or modifies entries in a camera initial exposure station file, interactively, for the imagery group referenced by a sub-block. 💅

🔑 KEYWORDS 🔑

imagery, orthorectify

🌈 SYNOPSIS 🌈

i.ortho.init
i.ortho.init --help
i.ortho.init [-rp] group=name  [xc=float]   [yc=float]   [zc=float]
[xc_sd=float]   [yc_sd=float]   [zc_sd=float]   [omega=float]
[phi=float]   [kappa=float]   [omega_sd=float]   [phi_sd=float]
[kappa_sd=float]   [--help]  [--verbose]  [--quiet]  [--ui]

🚩 Flags

  • -r — Use initial values at run time
  • -p — Print initial values
  • --help — Print usage summary
  • --verbose — Verbose module output
  • --quiet — Quiet module output
  • --ui — Force launching GUI dialog

🎛️ Parameters

  • group=name [required] — Name of imagery group for ortho-rectification
  • xc=float — Initial Camera Exposure X-coordinate
  • yc=float — Initial Camera Exposure Y-coordinate
  • zc=float — Initial Camera Exposure Z-coordinate
  • xc_sd=float — Apriori X-coordinate standard deviation
  • yc_sd=float — Apriori Y-coordinate standard deviation
  • zc_sd=float — Apriori Z-coordinate standard deviation
  • omega=float — Initial Camera Omega (pitch) degrees
  • phi=float — Initial Camera Phi (roll) degrees
  • kappa=float — Initial Camera Kappa (yaw) degrees
  • omega_sd=float — Apriori Omega (pitch) standard deviation
  • phi_sd=float — Apriori Phi (roll) standard deviation
  • kappa_sd=float — Apriori Kappa (yaw) standard deviation

🦋 DESCRIPTION 🦋

so. aerial photographs can be either vertical or oblique, and that distinction is the whole reason this module exists, no cap.

Vertical photographs can be truly vertical (nadir), or slightly tilted — less than 3 degree from the vertical. Usually aerial photos are tilted to some degree, because life is messy. We refer to the term vertical photograph up to a tilt of 3 degree.

Oblique aerial photographs are purposely taken with an angle between 3 and 90 degree from the nadir direction. on purpose!! artistic choice!! 👑

The use of i.ortho.init (menu 6) is only required when rectifying a tilted or oblique aerial photo. if your photo is perfectly behaved you can skip this whole thing, periodt.

i.ortho.init creates or modifies entries in a camera initial exposure station file for the imagery group referenced by a sub-block. These entries include:

  • the (XC,YC,ZC) standard (e.g. UTM) approximate coordinates of the camera exposure station;
  • initial roll, pitch, and yaw angles (in degrees) of the camera's attitude;
  • and the a priori standard deviations for these parameters.

During the imagery program, i.ortho.rectify, the initial camera exposure station file is used for computation of the ortho-rectification parameters. And if no initial camera exposure station file exists? the default values are computed from the control points file created in g.gui.image2target. so it's not the end of the world, but like, give it the file. 🫶

🎀 the menu that shows up

The following menu is displayed:

        Please provide the following information
    INITIAL XC: Meters                __________
    INITIAL YC: Meters                __________
    INITIAL ZC: Meters                __________
    INITIAL omega (pitch) degrees:    __________
    INITIAL phi  (roll) degrees:      __________
    INITIAL kappa  (yaw) degrees:     __________
    Standard Deviation XC: Meters     __________
    Standard Deviation YC: Meters     __________
    Standard Deviation ZC: Meters     __________
    Std. Dev. omega (pitch) degrees:  __________
    Std. Dev. phi  (roll) degrees:    __________
    Std. Dev. kappa  (yaw) degrees:   __________
        Use these values at run time? (1=yes, 0=no)
     AFTER COMPLETING ALL ANSWERS, HIT <ESC> TO CONTINUE
                  (OR <Ctrl-C> TO CANCEL)
bestie please read that last part again: AFTER COMPLETING ALL ANSWERS, HIT <ESC> TO CONTINUE and (OR <Ctrl-C> TO CANCEL). <ESC> = keep it, <Ctrl-C> = nope out. 💀

🌸 the INITIAL values

The INITIAL values for (XC,YC,ZC) are expressed in standard (e.g. UTM) coordinates, and represent an approximation for the location of the camera at the time of exposure.

  • X: East aircraft position;
  • Y: North aircraft position;
  • Z: Flight altitude above sea level

The INITIAL values for (omega,phi,kappa) are expressed in degrees, and represent an approximation for the camera's attitude at the time of exposure.

  • Omega (pitch): Raising or lowering of the aircraft's front (turning around the wings' axis);
  • Phi (roll): Raising or lowering of the wings (turning around the aircraft's axis);
  • Kappa (yaw): Rotation needed to align the aerial photo to true north: needs to be denoted as +90 degree for clockwise turn and -90 degree for a counterclockwise turn.

If ground control points are available, the INITIAL values are iteratively corrected. This is particularl useful when the INITIAL values are rather rough estimates. (yes, that typo is in the original and we love her for it 💖)

🧚 the standard deviations

The standard deviations for (XC,YC,ZC) are expressed in meters, and are used as a priori values for the standard deviations used in computation of the ortho rectification parameters. Higher values improve the refinement of the initial camera exposure. As a rule of thumb, 5% of the estimated target extents should be used.

The standard deviations for (omega,phi,kappa) are expressed in degrees, and are used as a priori values for the standard deviations used in computation of the ortho rectification parameters. As a rule of thumb, 2 degrees should be used.

If Use these values at run time? (1=yes, 0=no) is set to 0, the values in this menu are not used. like they just sit there. unbothered. unutilised. 🙈

👀 SEE ALSO 👀

i.ortho.photo, g.gui.photo2image, g.gui.image2target, i.ortho.elev, i.ortho.camera, i.ortho.transform, i.ortho.rectify

👑 AUTHOR 👑

Mike Baba, DBA Systems, Inc.

💻 SOURCE CODE 💻

Available at: i.ortho.init source code (history)

Accessed: Saturday Jan 17 05:41:44 2026

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

and that's the whole page bestie — this was i.ortho.init(1) from the GRASS 8.4.2 reference manual, manual page i.ortho.init(1), and you absolutely ate it. go rectify something gorgeous. 💅✨🦋

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