Homography example (#242)

* add homography files

* fixed some minor bugs

* No bugs for homography_estimation.py

* isorted homography_estimation.py

* added copyright notice

* removed some comments

* added some comments describing the fns

* Moved third_party code to a separate folder.

* Updated README with homography dependencies.

* moved layer init to top, fixed visualisation bug

- removed tensorboard loggin
- put theseus layer init outside of loop
- fixed bug with visualisation using state history

* Changed viz directory.

* added description in examples readme

Co-authored-by: Daniel DeTone <4764838+ddetone@users.noreply.github.com>
Co-authored-by: Joseph Ortiz <20665119+joeaortiz@users.noreply.github.com>
Co-authored-by: Luis Pineda <luisen.p@gmail.com>

.gitignore

@@ -20,4 +20,5 @@ datasets/
 data/
 temp/
 scripts/
-docs_build/
+docs_build/
+viz/

examples/README.md

@@ -15,6 +15,8 @@ problem with loop closure outliers.
 - pose_graph/pose_graph_benchmark: Is an example of using Theseus to solve pose graph optimization problems.
 - pose_graph/pose_graph_g2o: Is an example of using Theseus to solve pose graph optimization problems in the
 g2o format.
+- homography_estimation.py: Is an example of using Theseus to learn CNN image features for homography estimation.
+The features are trained to minimize the four corner distance between the warped and target image.
 
 These can be run from your root `theseus` directory by doing
 
@@ -27,11 +29,19 @@ These can be run from your root `theseus` directory by doing
     python examples/pose_graph/pose_graph_cube
     python examples/pose_graph/pose_graph_benchmark
     python examples/pose_graph/pose_graph_g2o
+    python examples/homography_estimation.py
 
-The motion planning and tactile estimation examples require `hydra` installation which you can obtain
+The motion planning and tactile estimation examples require `hydra` installation, which you can obtain
 by running.
 
     pip install hydra-core
 
+The homography example requires `kornia` and `OpenCV`, which you can install with
+
+```bash
+    pip install kornia
+    pip install opencv-python
+```
+
 Any outputs generated by these scripts will be saved under `examples/outputs`. You can 
 change this directory by passing the CLI option `hydra.run.dir=<your_directory>`