Readme and return type changes (#1) (#2)

* Fixed a wrong comment/docstring

* Adding to README

* Fixing filename extension

* Some fixes and updates to README

* Fixing up return type

README.md

@@ -2,6 +2,40 @@
 
 Stereo RGB Image Bin to GeoTIFF Converter.
 
+### Sample Docker Command line
+Below is a sample command line that shows how the bin2tif Docker image could be run.
+An explanation of the command line options used follows.
+Be sure to read up on the [docker run](https://docs.docker.com/engine/reference/run/) command line for more information.
+
+```docker run --rm --mount "src=/home/test,target=/mnt,type=bind" agpipeline/bin2tif:2.0 --working_space "/mnt" --metadata "/mnt/08f445ef-b8f9-421a-acf1-8b8c206c1bb8_metadata_cleaned.json" "/mnt/08f445ef-b8f9-421a-acf1-8b8c206c1bb8_left.bin" ```
+
+This example command line assumes the source files are located in the `/home/test` folder of the local machine.
+The name of the image to run is `agpipeline/bin2tif:2.0`.
+
+We are using the same folder for the source files and the output files.
+By using multiple `--mount` options, the source and output files can be located in separate folders.
+
+**Docker commands** \
+Everything between 'docker' and the name of the image are docker commands.
+
+- `run` indicates we want to run an image
+- `--rm` automatically delete the image instance after it's run
+- `--mount "src=/home/test,target=/mnt,type=bind"` mounts the `/home/test` folder to the `/mnt` folder of the running image
+
+We mount the `/home/test` folder to the running image to make files available to the software in the image.
+
+**Image's commands** \
+The command line parameters after the image name are passed to the software inside the image.
+Note that the paths provided are relative to the running image (see the --mount option specified above).
+
+- `--working_space "/mnt"` specifies the folder to use as a workspace
+- `--metadata "/mnt/08f445ef-b8f9-421a-acf1-8b8c206c1bb8_metadata.cleaned.json"` is the name of the source metadata to be cleaned
+- `"/mnt/08f445ef-b8f9-421a-acf1-8b8c206c1bb8_left.bin"` is the name of the raw image to convert
+
+# Original README
+Below are the contents of the original README.md for the TERRA REF project.
+It is included here as reference material for the history of this transformer.
+
 ## Authors: 
 
 * Zongyang Li, Donald Danforth Plant Science Center, St. Louis, MO

transformer.py

@@ -21,12 +21,12 @@ def add_parameters(parser: argparse.ArgumentParser) -> None:
                         help='saves the intermediate image file before it\'s saved as a geotiff')
 
 # pylint: disable=unused-argument
-def check_continue(transformer: transformer_class.Transformer, check_md: dict, transformer_md: dict, full_md: dict) -> list:
+def check_continue(transformer: transformer_class.Transformer, check_md: dict, transformer_md: dict, full_md: dict) -> tuple:
     """Checks if conditions are right for continuing processing
     Arguments:
         transformer: instance of transformer class
     Return:
-        Returns a dictionary containining the return code for continuing or not, and
+        Returns a tuple containining the return code for continuing or not, and
         an error message if there's an error
     """
     have_file = False