i.ortho.photo(1grass) GRASS GIS User's Manual i.ortho.photo(1grass)
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
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
productname=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.rec-
tify
i.group: 1 - Select/Modify imagery group
i.ortho.target: 2 - Select/Modify imagery group target
i.ortho.elev: 3 - Select/Modify target elevation model
i.ortho.camera: 4 - Select/Modify imagery group camera
g.gui.photo2image: 5 - Compute image-to-photo transformation
i.ortho.init: 6 - Initialize exposure station parameters
g.gui.image2target: 7 - Compute ortho-rectification parameters
i.ortho.rectify: 8 - Ortho-rectify imagery files
DESCRIPTION
i.ortho.photo is a menu to launch the different parts of the ortho rec-
tification process of aerial imagery. i.ortho.photo allows the user to
ortho-rectify imagery group files consisting of several scanned aerial
photographs (raster maps) of a common area. i.ortho.photo guides the
user through 8 steps required to ortho-rectify the raster maps in a
single imagery group. Alternatively, all the steps can be performed
separately by running the appropriate modules.
• Initialization Options
• Create/Modify imagery group to be orthorectified: i.group
• Select/Modify target location and mapset for orthorectifica-
tion: i.ortho.target
• Select/Modify target elevation model used for orthorectifica-
tion: i.ortho.elev
• Create/Modify camera file of imagery group: i.ortho.camera
• 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
• Ortho-rectification
• Ortho-rectify imagery group: i.ortho.rectify
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 (image coordinate system) and the coordinate
system of the camera sensor in millimetres (photo coordinate system)
for the interior orientation of the image, and further to the georefer-
enced coordinate system defined by projection parametres (target coor-
dinate system) for exterior orientation.
EXAMPLE
Five groups of input parameters are required for ortho-rectification:
• Aerial image (images),
• Exposure and characteristics of the camera, i.e. its coordi-
nates 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.
Example of an input oblique image in a source location
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.
The aerial photos shall be stored in a source location - a general
Cartesian coordinate system (XY). Digital elevation model and a map
reference (topo sheet or other map used for ground control point match-
ing) shall be stored in a target location in a real-world coordinate
system (e.g. ETRS33).
The steps to follow are described below:
1 Create/Modify imagery group to be orthorectified: i.group
This step is to be run in the source location.
In this first step an imagery group of aerial images for ortho-rectifi-
cation 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 contatins the
names of all images in a group.
IMG_0020 source_mapset
IMG_0021 source_mapset
IMG_0022 source_mapset
2 Select/Modify target location and mapset for orthorectification:
i.ortho.target
This step is to be run in the source location.
The target location and mapset may be selected or modified in Step 2.
You will be prompted for the names of the projected target location and
mapset where the ortho-rectified raster maps will reside. The target
location is also the location 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 contatining the names of
target location and mapset.
ETRS_33N
target_mapset
3 Select/Modify target elevation model used for orthorectifica-
tion: i.ortho.elev
This step is to be run in the source location.
Step 3 allows you to select the raster map from the target location 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 lo-
cation 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 conta-
tining 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
This step is to be run in the source location.
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 impor-
tant characteristic of the camera is its focal length. Fiducial or re-
seau 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, contatining the
name of the reference camera and a file mapset/camera/name_of_refer-
ence, contatining 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 -7.7
5
Compute image-to-photo transformation: g.gui.photo2image
This step is to be run in the source location.
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 refer-
ence file. A new file mapset/group/name_of_group/REF_POINTS is created,
contatining a list of pairs of coordinates in image and photo coordi-
nate 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
Step 5: Image-to-photo transformation of an oblique image
6
Initialize parameters of camera: i.ortho.init
This step is to be run in the source location.
In Step 6, initial camera exposure station parameters and initial vari-
ances may be selected or modified.
• X: East aircraft position;
• Y: North aircraft position;
• Z: Flight heigh 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.
Principle of pitch and yaw
In Step 6, a new file mapset/group/name_of_group/INIT_EXP is created,
contatining 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) 0
7
Compute ortho-rectification parameters from ground control
points: g.gui.image2target
This step is to be run in the target location.
The photo to target transformation parameters, i.e. the "exterior ori-
entation", 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. Reason-
able 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, contatining a
list of pairs of coordinates of ground control points in photo and tar-
get 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
Step 7: Detail of ground control points matching in an oblique image
and terrain model
8
Ortho-rectify imagery group: i.ortho.rectify
This step is to be run in the source location.
Step 8 is used to perform the actual image ortho-rectification after
all of the transformation parameters have been computed. Ortho-recti-
fied raster files will be created in the target location for each se-
lected imagery group file. You may select either the current window in
the target location or the minimal bounding window for the ortho-recti-
fied image.
Step 8: Ortho-rectified oblique image As a result, the ortho-rectified
raster map is available for visualization and further image analysis.
REFERENCES
Wolf P.R. (1983). Elements of Photogrammetry: With Air Photo Interpre-
tation and Remote Sensing McGraw Hill Higher Education ISBN-10:
0070713456, ISBN-13: 978-0070713451
SEE ALSO
g.gui.image2target, g.gui.photo2image, i.group, i.ortho.camera, i.or-
tho.elev, i.ortho.init, i.ortho.rectify, i.ortho.target
AUTHOR
Mike Baba, DBA Systems, Inc.
GRASS development team, 199?-2017
SOURCE CODE
Available at: i.ortho.photo source code (history)
Accessed: unknown
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GRASS 7.8.7 i.ortho.photo(1grass)
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