README_opk_to_rpc.md

Convert opk to Rpc

opk_to_rpc Converts an opk file into a rational polynomial coefficients in QGIS GDAL format. If the file is in the same directory as the image, it will be read automatically and taken into account by the software. The z unit of the shots is the same as that of the DTM set as a parameter, so that RPCs can be used in QGIS or GDAL with the same DTM as here.

Application

Call the function from a terminal in the depot directory python borea_tools/opk_to_rpc.py. To view the information on the various parameters you can do :

python borea_tools/opk_to_rpc.py -h

Or if you install the package by pip the commande is:

opk-to-rpc -h

The parameters are:

Symbol	Details	Default	Mandatory
-r	File path of the workfile		V
-i	Type of each column in the site file. e.g. NXYZOPKC with Z in altitude	NXYZOPKC	X
-b	Order of rotation matrix axes.	opk	X
-u	Unit of the angle of shooting, 'degree' or 'radian'	degree	X
-a	True if z shot corrected by linear alteration	True	X
-f	Line number to start file playback. Does not take file header into account.	None	X
-z	Line number to end file playback. If not set, all lines below -l will be read.	None	X
-e	EPSG codifier number of the reference system used e.g. 2154	None	X
-y	Path to the file pyproj GeoTIFF of geoid.	None	X
--geog	EPSG codifier number of the reference geographic system, filled in if pyproj error	None	X
--geoc	EPSG codifier number of the reference geocentric system, filled in if pyproj error	None	X
-c	Files paths of cameras (.xml or .txt)	None	X
-m	DTM of the worksite.	None	X
--fm	Format of Dtm "altitude" or "height".	None	X, unless dtm is given
-x	To use an approximate system.	False	X
-w	Conversion path e.g. "./"	"./"	X
-o	Degree of the polynomial of the rpc (1, 2, 3)	3	X
-d	Size of the grid to calculate Rpc.	100	X
-l	Factor Rpc to replace pyproj convertion.	None	X
--oe	Code epsg for output data. If none keeps the input data projection.	None	X

E.G.

python ./borea_tools/opk_to_rpc.py -r ./dataset/23FD1305_alt_test.OPK -i NXYZOPKC -f 2 -c ./dataset/Camera1.txt -e 2154 -y ./dataset/fr_ign_RAF20.tif -m ./dataset/MNT_France_25m_h_crop.tif --fm height -o 3

or pip

opk-to-rpc -r ./dataset/23FD1305_alt_test.OPK -i NXYZOPKC -f 2 -c ./dataset/Camera1.txt -e 2154 -y ./dataset/fr_ign_RAF20.tif -m ./dataset/MNT_France_25m_h_crop.tif --fm height -o 3

Detail for the header of file -i and -o

header is used to describe the format of the opk file read. It provides information on what's in each column, and gives the data unit for Z and angles.
Type is:

Symbol	Details
S	to ignore the column just for -i
N	name of shot
X	coordinate x of the shot position
Y	coordinate y of the shot position
Z	coordinate z altitude of the shot position
H	coordinate z height of the shot position
O	omega rotation angle
P	phi rotation angle
K	kappa rotation angle
C	name of the camera

Detail for reading files

To read the opk file, you can select a line interval to be read using the -f parameter for the first line and -z for the last line. If not set, the entire file will be read. Please note that the header in the file is not taken into account and must therefore either be skipped with the -f parameter or commented out with a # at the beginning of the line. You can therefore add comments to the file with a # at the beginning of the line.

Camera file format

The camera file is a txt file, containing 6 pieces of information about the camera : its name (str), ppax (float), ppay (float), focal (float), image size: width (int) and height (int) in pixels.
Ppax and ppay are the main points of image deformation in x and y directions.
Each line of the file corresponds to a piece of information, starting with the type = info.

name = UCE-M3-f120-s06
ppax = 13210.00
ppay = 8502.00
focal = 30975.00
width = 26460
height = 17004

Only these 7 pieces of information will be read. You can add comments with a # in the first element of the line or other type = info, but they will not be read by the tool, unless the attribute has been added to the Camera class. An example file can be found in ./dataset/Camera1.txt.
No camera-related distortion is taken into account (distortion-free camera).

Detail for projection

This library can transform and process 3D data with a z in altitude or height. This is done by the pyproj library, which needs the geoid at site level to change units.

The command for adding a geoid is -y, where you can enter the paths to the various geoids. If the file is stored in pyproj's native folder (pyproj.datadir.get_data_dir(), usr/share/proj or env_name_folder/lib/python3.10/site-packages/pyproj/proj_dir/share/proj) the file name is sufficient pyproj will find it on its own. Geoids file can be found on pyproj's github (https://github.com/OSGeo/PROJ-data).

This transformation is accompanied by other cartographic, geographic and geocentric transformations. And pyproj may not be able to find the other systems on its own.
e.g.

>>>crsm = crs.CRS.from_epsg(4326)
>>>crs_geoc = pyproj.crs.GeocentricCRS(name=crsm.name, datum=crsm.datum.name)
File "...", line 171, in <module>
    crs_geoc = pyproj.crs.GeocentricCRS(name=crsm.name, datum=crsm.datum.name)
  File "...", line 1918, in __init__
    super().__init__(geocentric_crs_json)
  File "...", line 348, in __init__
    self._local.crs = _CRS(self.srs)
  File "pyproj/_crs.pyx", line 2378, in pyproj._crs._CRS.__init__
pyproj.exceptions.CRSError: Invalid projection: 

You can therefore specify as parameters the epsg ( --geog / --geoc ) you want to use for each type of projection.