mrcal-graft-models - Combines the intrinsics of one cameramodel with the extrinsics of another

```
# We have intrinsics.cameramodel containing improved intrinsics from a later
# calibration, and extrinsics.cameramodel that has the old intrinsics, but the
# right extrinsics
$ mrcal-graft-models
intrinsics.cameramodel
extrinsics.cameramodel
> joint.cameramodel
Combined
intrinsics from 'intrinsics.cameramodel'
Extrinsics from 'exrinsics.cameramodel'
$ mrcal-show-projection-diff
joint.cameramodel
extrinsics.cameramodel
[A plot pops up showing a low difference, just representing the two sets of
intrinsics. The recalibrated models have a large implied extrinsics
difference, but the diff tool computed and applised the implied
transformation]
$ mrcal-show-projection-diff
--radius 0
joint.cameramodel
extrinsics.cameramodel
[A plot pops up showing a high difference. Here the diff tool didn't apply the
implied transformation, so the differences in extrinsics are evident. Thus
here, joint.cameramodel is not a drop-in replacement for
extrinsics.cameramodel]
$ mrcal-graft-models
--radius -1
intrinsics.cameramodel
extrinsics.cameramodel
> joint.cameramodel
Transformation cam1 <-- cam0: rotation: 8.429 degrees, translation: [0. 0. 0.] m
Combined
intrinsics from 'intrinsics.cameramodel'
Extrinsics from 'exrinsics.cameramodel'
$ mrcal-show-projection-diff
--radius 0
joint.cameramodel
extrinsics.cameramodel
[A plot pops up showing a low difference. The graft tool applied the implied
transformation, so the models match without the diff tool needing to transform
anything. Thus here, joint.cameramodel IS a drop-in replacement for
extrinsics.cameramodel]
```

This tool combines intrinsics and extrinsics from different sources into a single model. The output is written to standard output.

A common use case is a system where the intrinsics are calibrated prior to moving the cameras to their final location, and then computing the extrinsics separately after the cameras are moved.

If we have computed such a combined model, and we decide to recompute the intrinsics afterwards, we can graft the new intrinsics to the previous extrinsics. By default, this wouldn't be a drop-in replacement for the previous model, since the intrinsics come with an implied geometric transformation, which will be different in the new intrinsics. By passing a non-zero --radius value, we can compute and apply the implied geometric transformation, so the combined model would be usable as a drop-in replacement.

The implied transformation logic is controlled by a number of commandline arguments, same ones as used by the mrcal-show-projection-diff tool. The only difference in options is that THIS tool uses --radius 0 by default, so we do not compute or apply the implied transformation unless asked. Pass --radius with a non-zero argument to compute and apply the implied transformation.

```
intrinsics Input camera model for the intrinsics. If "-" is given,
we read standard input. Both the intrinsics and
extrinsics sources may not be "-"
extrinsics Input camera model for the extrinsics. If "-" is given,
we read standard input. Both the intrinsics and
extrinsics sources may not be "-"
```

```
-h, --help show this help message and exit
--gridn GRIDN GRIDN Used if we're computing the implied-by-the-intrinsics
transformation. How densely we should sample the
imager. By default we use a 60x40 grid
--distance DISTANCE Used if we're computing the implied-by-the-intrinsics
transformation. By default we compute the implied
transformation for points infinitely far away from the
camera. If we want to look closer in, the desired
observation distance can be given in this argument. We
can also fit multiple distances at the same time by
passing them here in a comma-separated, whitespace-less
list
--where WHERE WHERE Used if we're computing the implied-by-the-intrinsics
transformation. Center of the region of interest used
for the transformation fit. It is usually impossible
for the models to match everywhere, but focusing on a
particular area can work better. The implied
transformation will be fit to match as large as
possible an area centered on this argument. If omitted,
we will focus on the center of the imager
--radius RADIUS Used if we're computing the implied-by-the-intrinsics
transformation. Radius of the region of interest. If
==0 (the default), we do NOT fit an implied
transformation at all. If <0, we use a "reasonable"
value: the whole imager if we're using uncertainties,
or min(width,height)/6 if --no-uncertainties. To fit
with data across the whole imager in either case, pass
in a very large radius
--no-uncertainties Used if we're computing the implied-by-the-intrinsics
transformation. By default we use the uncertainties in
the model to weigh the fit. This will focus the fit on
the confident region in the models without --where or
--radius. The computation will run faster with --no-
uncertainties, but the default --where and --radius may
need to be adjusted
```

https://www.github.com/dkogan/mrcal

Dima Kogan, `<dima@secretsauce.net>`

Copyright (c) 2017-2021 California Institute of Technology ("Caltech"). U.S. Government sponsorship acknowledged. All rights reserved.

Licensed under the Apache License, Version 2.0 (the "License"); You may obtain a copy of the License at

`http://www.apache.org/licenses/LICENSE-2.0`