Coding Conventions in the WATCH REPO
====================================

This document is an effort to list concepts and patterns that you will see if
you work in this repo that may cause confusion unless you have this prior
knowledge. In some cases we may try to make the code more clear in the future,
but in other cases these patterns bring enough of a benefit that we require
prerequisite knowledge.

This is not necesarilly a style guide, it simply documents the patterns that
you will encounter. Some of these are recommended, while others we are
modifying. When possible we will note this.


NOTE: If you find a coding pattern or abbreviation that confused you at first,
please contribute it here!


Common abbreviations:

* GSD - ground sample distance


Variable abbreviations:

* ``aid`` - annotation id - try to use ``annot_id`` instead

* ``gid`` - imaGe id - try to use ``image_id`` instead

* ``cid`` - category id  - try to use ``category_id`` instead

* A suffix of ``x`` or ``idx`` - an index (e.g. ``cx`` for category index)

* ``tr`` often means "target", but that pattern has been deprecated and its usually just spelled out as ``target`` now.

* The "xywh", "ltrb", and "cxywh" are codes indicating the format of bounding boxes for `kwimage.Boxes <https://kwimage.readthedocs.io/en/release/kwimage.structs.boxes.html#module-kwimage.structs.boxes>`_. They stand for "left-x, top-y, width, height", "left-x, top-y, right-x, bottom-y", and "center-x, center-y, width, height" respectively.

* ``dsize`` - This ALWAYS means a (width, height) pair, usually a ``Tuple[int, int]``, but not always. In VERY rare circumstances, an individual width or height may be None to represent that it is not known or needed to be specified. This is a recommended pattern; please follow this.

* ``shape`` - This is going to be the row-major shape of an array usually. Often (h, w, channel) or just (h, w).  This is a recommended pattern; please follow this.

* ``fpath`` - a "file" path. This is used to store a string of ``Path`` object representing a path that points to a file (i.e. not a directory).  This is a recommended pattern; please follow this.

* ``dpath`` - a "directory" path. This is used to store a string of ``Path`` object representing a path that points to a directory (i.e. not a file). This is a recommended pattern; please follow this.


Notes on row-vs-column major coordinate axes:

Because numpy makes heavy use of row-major indexing and opencv uses
column-major indexing, it is worth developing a separate notation for when one
style of indexing is being used so we do not confuse them.

* Variables named ``dsize`` / ``size``  or used with ``cv2`` / ``warping``
  operations will use a column-major (i.e. [x, y]) indexing style. Think
  width/height when you see these patterns.


* Variables named ``dims``, ``shape`` or used in numpy / torch / array
  logic will use a row-major (i.e. [r, c]) indexing style. Think row /
  column when you see these patterns.


Misc termonology:

* Functions / methods called "coerce" are designed to auto-detect the type of
  data that is given to them and then convert it into a stanardized expected
  type. These allow you to write functions that accept multiple different input
  formats, but guarentee a single output format.  For instace
  kwcoco.CocoDataset.coerce will accept either a file path to a kwcoco file, an
  existing kwcoco dataset, or a special string indicating the type of demodata
  to produce, but the outptut is always a kwcoco.CocoDataset object. Another
  example is watch.util_gis.coerce_geojson_datas, which can take one or more
  json objects, path to json files, glob patterns, paths to files containing
  lists of json files, etc, but the output is always the json data. Using these
  coerce methods should be done with care and never in a critical loop because
  they are slower than more direct methods and more prone to unintended
  results, but the flexibile behavior can be very convinient, and it is often
  worth using in system entry points before core logic takes place.


Short semi-ambiguous identifiers:

    * ``ub.udict`` - The extended ubelt dictionary with set operations and other nice methods

    * ``ub.ddict`` - A defaultdict alias


Module aliases

* ``import ubelt as ub``

* ``import numpy as np``

* ``import networkx as nx``

* ``import geopandas as gpd``

* ``import pytorch_lightning as pl``

* ``import geopandas as gpd``

* ``import pandas as pd``

* ``import seaborn as sns``

* ``import scriptconfig as scfg``


Best Practices:

* When you are working with a list of classes, try to make sure you have it wrapped in a ``kwcoco.CategoryTree`` and use that to shuffle around relevant metadata.

* When working with a set of channels wrt to a single sensor use: ``kwcoco.ChannelSpec`` or  ``kwcoco.FusedChannelSpec``

* When working with a set of channels wrt to known or unknown sensors use: ``kwcoco.SensorChanSpec`` or  ``kwcoco.FusedSensorChanSpec``

* DONT IMPORT PYPLOT AT THE MODULE LEVEL!!! Always do it in a function. If fact, do most everything inside a function. Reduce the amount of globally scoped code.


Spaces
------

See `KWCOCO Spaces <https://kwcoco.readthedocs.io/en/release/concepts/warping_and_spaces.html>`_ section in the in kwcoco docs.


There are several 'spaces' here and that can get confusing.

**Native Space** / **Asset Space** - The space of the data on disk

**Image Space** - The space all bands in an image are aligned to.

**Video Space** - The space a sequence is geo-aligned in.  This is the space we generally want to be thinking in.
    It is hard coded wrt to the kwcoco dataset.

**Window Space** - GSD the sliding window is expressed in.
   Defaults to video space.
   Computes a integer-sized box as the 'space_slice' in video space.
   Effectively this space is only used to compute the size of the box
   in the underlying video space. It does nothing else.
   Alias: Grid Space

**Input Space** - GSD of the input to the network
   Computes a scale factor relative to video space.
   Alias: Sample Space
   Alias: Data Space

**Output Space** - GSD of the output of the network
   Scale factor is wrt to video space.
   Alias: Prediction Space


The following visualizes the key asset, image, and video spaces:

.. image:: https://i.imgur.com/QuiSJwR.png
