Simplify proj params

.gitignore

@@ -130,4 +130,4 @@ cython_debug/
 .DS_Store
 
 # pixi environments
-.pixi
+.pixi

README.md

@@ -4,6 +4,8 @@
 
 _An Xarray extension for Google Earth Engine._
 
+Xee bridges the gap between Google Earth Engine's massive data catalog and the scientific Python ecosystem. It provides a custom Xarray backend that allows you to open any `ee.ImageCollection` as if it were a local `xarray.Dataset`. Data is loaded lazily and in parallel, enabling you to work with petabyte-scale archives of satellite and climate data using the power and flexibility of Xarray and its integrations with libraries like Dask.
+
 [![image](https://img.shields.io/pypi/v/xee.svg)](https://pypi.python.org/pypi/xee)
 [![image](https://static.pepy.tech/badge/xee)](https://pepy.tech/project/xee)
 [![Conda
@@ -32,85 +34,206 @@ Then, authenticate Earth Engine:
 earthengine authenticate --quiet
 ```
 
-Now, in your Python environment, make the following imports:
+Now, in your Python environment, make the following imports and initialize the Earth Engine client with your project ID. Using the high-volume API endpoint is recommended.
 
 ```python
 import ee
-import xarray
+import xarray as xr
+from xee import helpers
+import shapely
+
+ee.Initialize(
+    project='PROJECT-ID',  # Replace with your project ID
+    opt_url='https://earthengine-highvolume.googleapis.com'
+)
 ```
 
-Next, specify your EE-registered cloud project ID and initialize the EE client
-with the high volume API:
+### Specifying the Output Grid
+
+To open a dataset, you must specify the desired output pixel grid. The `xee.helpers` module simplifies this process by providing several convenient workflows, summarized below.
+
+| Goal | Method | When to Use |
+| :--- | :--- | :--- |
+| **Match Source Grid** | Use `helpers.extract_grid_params()` to get the parameters from an EE object. | When you want the data in its original, default projection and scale. |
+| **Fit Area to a Shape** | Use `helpers.fit_geometry()` with the `geometry` and `grid_shape` arguments. | When you need a consistent output array size (e.g., for ML models) and the exact pixel size is less important. |
+| **Fit Area to a Scale** | Use `helpers.fit_geometry()` with the `geometry` and `grid_scale` arguments. | When the specific resolution (e.g., 30 meters, 0.01 degrees) is critical for your analysis. |
+| **Manual Override** | Pass `crs`, `crs_transform`, and `shape_2d` directly to `xr.open_dataset`. | For advanced cases where you already have an exact grid definition. |
+
+> **Important Note on Units:** All grid parameter values must be in the units of the specified Coordinate Reference System (`crs`).
+> * For a geographic CRS like `'EPSG:4326'`, the units are in **degrees**.
+> * For a projected CRS like `'EPSG:32610'` (UTM), the units are in **meters**.
+> This applies to the translation values in `crs_transform` and the pixel sizes in `grid_scale`.
+
+### Usage Examples
+
+Here are common workflows for opening datasets with `xee`, corresponding to the methods in the table above.
+
+#### Match Source Grid
+
+This is the simplest case, using `helpers.extract_grid_params` to match the dataset's default grid.
 
 ```python
-ee.Initialize(
-    project='my-project-id'
-    opt_url='https://earthengine-highvolume.googleapis.com')
+ic = ee.ImageCollection('ECMWF/ERA5_LAND/MONTHLY_AGGR')
+grid_params = helpers.extract_grid_params(ic)
+ds = xr.open_dataset(ic, engine='ee', **grid_params)
 ```
 
-Open any Earth Engine ImageCollection by specifying the Xarray engine as `'ee'`:
+#### Fit Area to a Shape
+
+Define a grid over an area of interest by specifying the number of pixels. `helpers.fit_geometry` will calculate the correct `crs_transform`.
 
 ```python
-ds = xarray.open_dataset('ee://ECMWF/ERA5_LAND/HOURLY', engine='ee')
+aoi = shapely.geometry.box(113.33, -43.63, 153.56, -10.66) # Australia
+grid_params = helpers.fit_geometry(
+    geometry=aoi,
+    grid_crs='EPSG:4326',
+    grid_shape=(256, 256)
+)
+
+ds = xr.open_dataset('ee://ECMWF/ERA5_LAND/MONTHLY_AGGR', engine='ee', **grid_params)
 ```
 
-Open all bands in a specific projection (not the Xee default):
+#### Fit Area to a Scale (Resolution)
+
+> **A Note on `grid_scale` and Y-Scale Orientation**
+> When using `fit_geometry` with `grid_scale`, you are defining both the pixel size and the grid's orientation via the sign of the y-scale.
+> * A **negative `y_scale`** (e.g., `(10000, -10000)`) is the standard for "north-up" satellite and aerial imagery, creating a grid with a **top-left** origin.
+> * A **positive `y_scale`** (e.g., `(10000, 10000)`) is used by some datasets and creates a grid with a **bottom-left** origin.
+> You may need to inspect your source dataset's projection information to determine the correct sign to use. If you use `grid_shape`, a standard negative y-scale is assumed.
+
+The following example defines a grid over an area by specifying the pixel size in meters. `fit_geometry` will reproject the geometry and calculate the correct `shape_2d`.
 
 ```python
-ds = xarray.open_dataset('ee://ECMWF/ERA5_LAND/HOURLY', engine='ee',
-                         crs='EPSG:4326', scale=0.25)
+aoi = shapely.geometry.box(113.33, -43.63, 153.56, -10.66) # Australia
+grid_params = helpers.fit_geometry(
+    geometry=aoi,
+    geometry_crs='EPSG:4326',       # CRS of the input geometry
+    grid_crs='EPSG:32662',          # Target CRS in meters (Plate Carrée)
+    grid_scale=(10000, -10000)      # Define a 10km pixel size
+)
+
+ds = xr.open_dataset('ee://ECMWF/ERA5_LAND/MONTHLY_AGGR', engine='ee', **grid_params)
 ```
 
-Open an ImageCollection (maybe, with EE-side filtering or processing):
+#### Open a Custom Region at Source Resolution
+
+This workflow is ideal for analyzing a specific area while maintaining the dataset's original resolution.
 
 ```python
-ic = ee.ImageCollection('ECMWF/ERA5_LAND/HOURLY').filterDate(
-    '1992-10-05', '1993-03-31')
-ds = xarray.open_dataset(ic, engine='ee', crs='EPSG:4326', scale=0.25)
+# 1. Get the original grid parameters from the target ImageCollection
+ic = ee.ImageCollection('ECMWF/ERA5_LAND/MONTHLY_AGGR')
+source_params = helpers.extract_grid_params(ic)
+
+# 2. Extract the source CRS and scale
+source_crs = source_params['crs']
+source_transform = source_params['crs_transform']
+source_scale = (source_transform[0], source_transform[4]) # (x_scale, y_scale)
+
+# 3. Use the source parameters to fit the grid to a specific geometry
+aoi = shapely.geometry.box(113.33, -43.63, 153.56, -10.66) # Australia
+final_grid_params = helpers.fit_geometry(
+    geometry=aoi,
+    geometry_crs='EPSG:4326',
+    grid_crs=source_crs,
+    grid_scale=source_scale
+)
+
+# 4. Open the dataset with the final, combined parameters
+ds = xr.open_dataset(ic, engine='ee', **final_grid_params)
 ```
 
-Open an ImageCollection with a specific EE projection or geometry:
+#### Manual Override
+
+For use cases where you know the exact grid parameters, you can provide them directly.
 
 ```python
-ic = ee.ImageCollection('ECMWF/ERA5_LAND/HOURLY').filterDate(
-    '1992-10-05', '1993-03-31')
-leg1 = ee.Geometry.Rectangle(113.33, -43.63, 153.56, -10.66)
-ds = xarray.open_dataset(
-    ic,
+# Manually define a 512x512 pixel grid with 1-degree pixels in EPSG:4326
+manual_crs = 'EPSG:4326'
+manual_transform = (0.1, 0, -180.05, 0, -0.1, 90.05) # Values are in degrees
+manual_shape = (512, 512)
+
+ds = xr.open_dataset(
+    'ee://ECMWF/ERA5_LAND/MONTHLY_AGGR',
     engine='ee',
-    projection=ic.first().select(0).projection(),
-    geometry=leg1
+    crs=manual_crs,
+    crs_transform=manual_transform,
+    shape_2d=manual_shape,
 )
 ```
 
-Open multiple ImageCollections into one `xarray.Dataset`, all with the same
-projection:
+#### Open a Pre-Processed ImageCollection
+
+A key feature of Xee is its ability to open a computed `ee.ImageCollection`. This allows you to leverage Earth Engine's powerful server-side processing for tasks like filtering, band selection, and calculations before loading the data into Xarray.
 
 ```python
-ds = xarray.open_mfdataset(
-    ['ee://ECMWF/ERA5_LAND/HOURLY', 'ee://NASA/GDDP-CMIP6'],
-    engine='ee', crs='EPSG:4326', scale=0.25)
+# Define an AOI as a shapely object for the helper function
+sf_aoi_shapely = shapely.geometry.Point(-122.4, 37.7).buffer(0.2)
+# Create an ee.Geometry from the shapely object for server-side filtering
+coords = list(sf_aoi_shapely.exterior.coords)
+sf_aoi_ee = ee.Geometry.Polygon(coords)
+
+# Define a function to calculate NDVI and add it as a band
+def add_ndvi(image):
+    # Landsat 9 SR bands: NIR = B5, Red = B4
+    ndvi = image.normalizedDifference(['SR_B5', 'SR_B4']).rename('NDVI')
+    return image.addBands(ndvi)
+
+# Build the pre-processed collection
+processed_collection = (ee.ImageCollection('LANDSAT/LC09/C02/T1_L2')
+    .filterDate('2024-06-01', '2024-09-01')
+    .filterBounds(sf_aoi_ee)
+    .map(add_ndvi)
+    .select(['NDVI']))
+
+# Define the output grid using a helper
+grid_params = helpers.fit_geometry(
+    geometry=sf_aoi_shapely,
+    grid_crs='EPSG:32610',     # Target CRS in meters (UTM Zone 10N)
+    grid_scale=(30, -30)        # Use Landsat's 30m resolution
+)
+
+# Open the fully processed collection
+ds = xr.open_dataset(processed_collection, engine='ee', **grid_params)
 ```
 
-Open a single Image by passing it to an ImageCollection:
+#### Open a single Image
+
+The `helpers` work the same way for a single `ee.Image`.
 
 ```python
-i = ee.ImageCollection(ee.Image('LANDSAT/LC08/C02/T1_TOA/LC08_044034_20140318'))
-ds = xarray.open_dataset(i, engine='ee')
+img = ee.Image('ECMWF/ERA5_LAND/MONTHLY_AGGR/202501')
+grid_params = helpers.extract_grid_params(img)
+ds = xr.open_dataset(img, engine='ee', **grid_params)
+```
+
+#### Visualize a Single Time Slice
+
+Once you have your `xarray.Dataset`, you can visualize a single time slice of a variable to verify the results. This requires the `matplotlib` library, which is an optional dependency.
+
+If you don't have it installed, you can add it with pip:
+
+```shell
+pip install matplotlib
 ```
 
-Open any Earth Engine ImageCollection to match an existing transform:
+Xarray's plotting functions expect dimensions in `(y, x)` order for 2D plots. Since the data is in `(x, y)` order, we use `.transpose()` to swap the axes for correct visualization.
 
 ```python
-raster = rioxarray.open_rasterio(...) # assume crs + transform is set
-ds = xr.open_dataset(
-    'ee://ECMWF/ERA5_LAND/HOURLY',
-    engine='ee',
-    geometry=tuple(raster.rio.bounds()), # must be in EPSG:4326
-    projection=ee.Projection(
-        crs=str(raster.rio.crs), transform=raster.rio.transform()[:6]
-    ),
+
+# First, open a dataset using one of the methods above
+aoi = shapely.geometry.box(113.33, -43.63, 153.56, -10.66) # Australia
+grid_params = helpers.fit_geometry(
+    geometry=aoi,
+    grid_crs='EPSG:4326',
+    grid_shape=(256, 256)
 )
+ds = xr.open_dataset('ECMWF/ERA5_LAND/MONTHLY_AGGR', engine='ee', **grid_params)
+
+# Select the 2m air temperature for the first time step
+temp_slice = ds['temperature_2m'].isel(time=0)
+
+# Transpose from (x, y) to (y, x) for correct plotting orientation and plot
+temp_slice.transpose('y', 'x').plot()
 ```
 
 See [examples](https://github.com/google/Xee/tree/main/examples) or

pyproject.toml

@@ -3,7 +3,7 @@ name = "xee"
 dynamic = ["version"]
 description = "A Google Earth Engine extension for Xarray."
 readme = "README.md"
-requires-python = ">=3.8"
+requires-python = ">=3.8,<3.13"
 license = {text = "Apache-2.0"}
 authors = [
   {name = "Google LLC", email = "noreply@google.com"},
@@ -28,6 +28,7 @@ dependencies = [
   "earthengine-api>=0.1.374",
   "pyproj",
   "affine",
+  "shapely",
 ]
 
 [project.entry-points."xarray.backends"]
@@ -65,5 +66,8 @@ preview = true
 pyink-indentation = 2
 pyink-use-majority-quotes = true
 
+[tool.setuptools]
+packages = ["xee"]
+
 [tool.setuptools_scm]
 fallback_version = "9999"