i.ortho.photo(1)
🌸 i.ortho.photo 💖
okay bestie, so this is the i.ortho.photo page from the GRASS GIS User's Manual — it's the menu driver situation, and she is long, so buckle up 🎀
✨ NAME ✨
i.ortho.photo — Menu driver for the photo imagery programs.
🔑 KEYWORDS 🔑
imagery, orthorectify, geometry
🦋 SYNOPSIS 🦋
i.ortho.photo
i.ortho.photo --help
i.ortho.photo group=name productname=string [--help] [--verbose] [--quiet] [--ui]⭐ Flags
--help— prints the usage summary for you, no cap--verbose— verbose module output (she talks more)--quiet— quiet module output (she talks less)--ui— force launching the GUI dialog, main character energy only
🎀 Parameters
group=name[required] — Name of imagery group for ortho-rectificationproductname=string[required] — Name of Modules
Options: i.group, i.ortho.target, i.ortho.elev, i.ortho.camera, g.gui.photo2image, i.ortho.init, g.gui.image2target, i.ortho.rectify
i.group: 1 - Select/Modify imagery groupi.ortho.target: 2 - Select/Modify imagery group targeti.ortho.elev: 3 - Select/Modify target elevation modeli.ortho.camera: 4 - Select/Modify imagery group camerag.gui.photo2image: 5 - Compute image-to-photo transformationi.ortho.init: 6 - Initialize exposure station parametersg.gui.image2target: 7 - Compute ortho-rectification parametersi.ortho.rectify: 8 - Ortho-rectify imagery files
💜 DESCRIPTION 💜
so i.ortho.photo is literally a menu that launches the different parts of the ortho rectification process for aerial imagery 🛩️ she lets you ortho-rectify imagery group files that are made up of several scanned aerial photographs (raster maps) covering a common area. and the way she does it? she walks you through all 8 steps you need to ortho-rectify the raster maps in a single imagery group 🫶
but wait — you don't have to do the whole tour with her. every step can also be done separately by just running the appropriate module yourself. pick your own adventure, periodt ✨
- Initialization Options
- Create/Modify imagery group to be orthorectified:
i.group - Select/Modify target project (formerly known as location) and mapset for orthorectification:
i.ortho.target - Select/Modify target elevation model used for orthorectification:
i.ortho.elev - Create/Modify camera file of imagery group:
i.ortho.camera
- Create/Modify imagery group to be orthorectified:
- Transformation Parameters Computation
- Compute image-to-photo transformation:
g.gui.photo2image - Initialize parameters of camera:
i.ortho.init - Compute ortho-rectification parameters from ground control points:
g.gui.image2target
- Compute image-to-photo transformation:
- Ortho-rectification
- Ortho-rectify imagery group:
i.ortho.rectify
- Ortho-rectify imagery group:
ngl the actual vibe of the whole procedure is so satisfying to understand: the ortho-rectification procedure in GRASS GIS places the image pixels on the surface of the earth 🌍 by matching the coordinate system of the aerial image in pixels (that's the image coordinate system) with the coordinate system of the camera sensor in millimetres (that's the photo coordinate system) — that pairing is what handles the interior orientation of the image — and then further to the georeferenced coordinate system defined by projection parametres (that's the target coordinate system) for the exterior orientation. like, interior then exterior, the two-step glow-up 💅
bestie don't go anywhere — this page keeps going, part 2 is coming 👀
✨ EXAMPLE ✨
okay bestie, so ortho-rectification needs five groups of input parameters, and no you cannot skip any of them, they're all main characters:
- Aerial image (
images), - Exposure and characteristics of the camera, i.e. its coordinates in target coordinate system and height above sea level, focal length, yaw, pitch and roll, dimensions of the camera sensor and resolution of aerial images,
- Reference surface, i.e. digital elevation model in the target coordinate system used to normalize the terrain undulation,
- Topographic reference map used to find corresponding ground control points and/or,
- Coordinates of ground control points in the target coordinate system.
📸 figure caption core: "Example of an input oblique image in a source project"
To ortho-rectify aerial images the user has to follow the menu options step by step. Alternatively, all the steps can be performed separately by running the corresponding modules. Both routes eat, honestly.
The aerial photos shall be stored in a source project — a general Cartesian coordinate system (XY). Digital elevation model and a map reference (topo sheet or other map used for ground control point matching) shall be stored in a target project in a real-world coordinate system (e.g. ETRS33).
The steps to follow are described below, and yes we're going through all of them 💅
1 — Create/Modify imagery group to be orthorectified: i.group
Run this one in the source project.
In this first step an imagery group of aerial images for ortho-rectification is created or modified. The current imagery group is displayed at the top of the menu. You may select a new or existing imagery group for the ortho-rectification. After choosing this option you will be prompted for the name of a new or existing imagery group. As a result, a new file mapset/group/name_of_group/REF is created that contains the names of all images in a group.
IMG_0020 source_mapset
IMG_0021 source_mapset
IMG_0022 source_mapset2 — Select/Modify target project and mapset for orthorectification: i.ortho.target
Also the source project, bestie.
The target project and mapset may be selected or modified in Step 2. You will be prompted for the names of the projected target project and mapset where the ortho-rectified raster maps will reside. The target project is also the project from which the elevation model (raster map) will be selected (see Step 3). In Step 2, a new file mapset/group/name_of_group/TARGET is created containing the names of target project and mapset.
ETRS_33N
target_mapset3 — Select/Modify target elevation model used for orthorectification: i.ortho.elev
Yep, source project again.
Step 3 allows you to select the raster map from the target project to be used as the elevation model. The elevation model is required for both the computation of photo-to-target parameters (Step 6) and for the ortho-rectification of the imagery group files (Step 8). The raster map selected for the elevation model should cover the entire area of the image group to be ortho-rectified. DTED and DEM files are suitable for use as elevation model in the ortho-rectification program. In Step 3 you will be prompted for the name of the raster map in the target project that you want to use as the elevation model. As a result of this step, a new file mapset/group/name_of_group/ELEVATION is created containing the name and mapset of the chosen DEM.
elevation layer :ELEVATION
mapset elevation:target_mapset
location :ETRS_33N
math expression :(null)
units :(null)
no data values :(null)4 — Create/Modify camera file of imagery group: i.ortho.camera
Source project. You know the drill 💖
In Step 4 you may select or create a camera reference file that will be used with the current imagery group. A camera reference file contains information on the internal characteristics of the aerial camera, as well as the geometry of the fiducial or reseau marks. The most important characteristic of the camera is its focal length. Fiducial or reseau marks locations are required to compute the scanned image to photo coordinate transformation parameter (Step 5). Two new files are created in this step: a file mapset/group/name_of_group/CAMERA, containing the name of the reference camera, and a file mapset/camera/name_of_reference, containing the camera parameters.
CAMERA NAME sony
CAMERA ID 123
CAMERA XP 0
CAMERA YP 0
CAMERA CFL 16
NUM FID 4
0 -11.6 0
1 0 7.7
2 11.6 0
3 0 -7.75 — Compute image-to-photo transformation: g.gui.photo2image
Source project, always source project, we stay in the source project.
The scanned image to photo coordinate transformation parameters, i.e. the "interior orientation", is computed in Step 5. In this interactive step you associate the scanned reference points (fiducials, reseau marks, etc.) with their known photo coordinates from the camera reference file. A new file mapset/group/name_of_group/REF_POINTS is created, containing a list of pairs of coordinates in image and photo coordinate systems.
# Ground Control Points File
#
# target location: XY
# target mapset: source_mapset
# source target status
# east north east north (1=ok, 0=ignore)
#-------------------------------------------------------------
0 1816 -11.6 0.0 1
2728 3632 0.0 7.7 1
5456 1816 11.6 0.0 1
2728 0.0 0.0 -7.7 1🦋 figure caption: "Step 5: Image-to-photo transformation of an oblique image"
6 — Initialize parameters of camera: i.ortho.init
Source project 🫶
In Step 6, initial camera exposure station parameters and initial variances may be selected or modified. Here's the lore on what each one actually means:
- X: East aircraft position;
- Y: North aircraft position;
- Z: Flight height above surface;
- 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° for clockwise turn and -90° for a counter-clockwise turn.
🌸 figure caption: "Principle of pitch and yaw"
In Step 6, a new file mapset/group/name_of_group/INIT_EXP is created, containing camera parameters.
INITIAL XC 215258.345387
INITIAL YC 6911444.022270
INITIAL ZC 1101.991120
INITIAL OMEGA 0.000000
INITIAL PHI -0.168721
INITIAL KAPPA 3.403392
VARIANCE XC 5.000000
VARIANCE YC 5.000000
VARIANCE ZC 5.000000
VARIANCE OMEGA 0.000000
VARIANCE PHI 0.020153
VARIANCE KAPPA 0.017453
STATUS (1=OK, 0=NOT OK) 07 — Compute ortho-rectification parameters from ground control points: g.gui.image2target
⚠️ plot twist, bestie: this step is to be run in the target project. Different project, different energy.
The photo to target transformation parameters, i.e. the "exterior orientation", is computed in Step 7. In this interactive step, control points are marked on one or more imagery group files and associated with the known standard (e.g. UTM) and elevation coordinates. Reasonable rectification results can be obtained with around twelve control points well distributed over the image. In this step, a new file mapset/group/name_of_group/CONTROL_POINTS is created, containing a list of pairs of coordinates of ground control points in photo and target coordinate systems.
# Ground Control Points File
#
# target location: ETRS_33N
# target mapset: target_mapset
# source target status
# east north height east north height (1=ok, 0=ignore)
#------------------------------ ---------------------- ---------------
98.3679932698 906.327649515 0.0 1.0 5.0 100.0 1
733.293023813 1329.61100321 0.0 2.0 6.0 100.0 1
1292.6317412 1703.76325335 0.0 3.0 7.0 100.0 1
1625.54617472 1368.11694482 0.0 4.0 6.0 100.3 1
3239.82849913 1390.97403968 0.0 7.4 6.0 100.3 1
1570.09788497 2790.06537829 0.0 3.0 11.0 100.0 1🔍 figure caption: "Step 7: Detail of ground control points matching in an oblique image and terrain model"
8 — Ortho-rectify imagery group: i.ortho.rectify
Back to the source project one final time 💜
Step 8 is used to perform the actual image ortho-rectification after all of the transformation parameters have been computed. Ortho-rectified raster files will be created in the target project for each selected imagery group file. You may select either the current window in the target project or the minimal bounding window for the ortho-rectified image.
👑 figure caption: "Step 8: Ortho-rectified oblique image" — and as a result, the ortho-rectified raster map is available for visualization and further image analysis. Periodt, you did it.
📚 REFERENCES 📚
Wolf P.R. (1983). Elements of Photogrammetry: With Air Photo Interpretation and Remote Sensing McGraw Hill Higher Education ISBN-10: 0070713456, ISBN-13: 978-0070713451
👀 SEE ALSO 👀
g.gui.image2targetg.gui.photo2imagei.groupi.ortho.camerai.ortho.elevi.ortho.initi.ortho.rectifyi.ortho.target
🫶 AUTHORS 🫶
Mike Baba, DBA Systems, Inc. GRASS development team, 199?-2017
🌈 SOURCE CODE 🌈
Available at: i.ortho.photo source code (history)
Accessed: Saturday Jan 17 05:41:44 2026
Main index | Imagery index | Topics index | Keywords index | Graphical index | Full index
© 2003-2025 GRASS Development Team, GRASS GIS 8.4.2 Reference Manual
and that's a wrap on the GRASS 8.4.2 i.ortho.photo(1) page, accessed Saturday Jan 17 05:41:44 2026 — go forth and ortho-rectify, you absolute icon 🎀✨💖
📦 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 : a language model's rewrite of the original, under its terms