paleolimbot commented on code in PR #749:
URL: https://github.com/apache/sedona-db/pull/749#discussion_r3121100458
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rust/sedona-schema/src/raster.rs:
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@@ -16,34 +16,33 @@
// under the License.
use arrow_schema::{DataType, Field, FieldRef, Fields};
-/// Schema for storing raster data in Apache Arrow format.
-/// Utilizing nested structs and lists to represent raster metadata and bands.
+/// Schema for storing N-dimensional raster data in Apache Arrow format.
+///
+/// Each raster has a CRS, an affine transform, explicit spatial dimension
names
+/// (`x_dim`, `y_dim`), and a list of bands. Each band is an N-D chunk with
named
+/// dimensions, a shape, and optional strides for zero-copy slicing.
+///
+/// Legacy 2D rasters are represented as bands with `dim_names=["y","x"]` and
+/// `shape=[height, width]`.
#[derive(Debug, PartialEq, Clone)]
pub struct RasterSchema;
+
impl RasterSchema {
/// Returns the top-level fields for the raster schema structure.
pub fn fields() -> Fields {
Fields::from(vec![
- Field::new(column::METADATA, Self::metadata_type(), false),
- Field::new(column::CRS, Self::crs_type(), true), // Optional: may
be inferred from data
+ Field::new(column::CRS, Self::crs_type(), true),
+ Field::new(column::TRANSFORM, Self::transform_type(), false),
+ Field::new(column::X_DIM, DataType::Utf8View, false),
+ Field::new(column::Y_DIM, DataType::Utf8View, false),
Field::new(column::BANDS, Self::bands_type(), true),
])
}
- /// Raster metadata schema
- pub fn metadata_type() -> DataType {
- DataType::Struct(Fields::from(vec![
- // Raster dimensions
- Field::new(column::WIDTH, DataType::UInt64, false),
- Field::new(column::HEIGHT, DataType::UInt64, false),
- // Geospatial transformation parameters
- Field::new(column::UPPERLEFT_X, DataType::Float64, false),
- Field::new(column::UPPERLEFT_Y, DataType::Float64, false),
- Field::new(column::SCALE_X, DataType::Float64, false),
- Field::new(column::SCALE_Y, DataType::Float64, false),
- Field::new(column::SKEW_X, DataType::Float64, false),
- Field::new(column::SKEW_Y, DataType::Float64, false),
- ]))
+ /// Affine transform schema — 6-element GDAL GeoTransform:
+ /// `[origin_x, scale_x, skew_x, origin_y, skew_y, scale_y]`
+ pub fn transform_type() -> DataType {
+ DataType::List(FieldRef::new(Field::new("item", DataType::Float64,
false)))
}
Review Comment:
> Sorry I'm not clear what you want me to do.
- Change `Field::new(column::X_DIM, DataType::Utf8View, false),
Field::new(column::Y_DIM, DataType::Utf8View, false)` to
`Field::new(column::DIMS, DataType::new_list(DataType::Utf8View), false)`. This
be of length 2 for now and you don't have to change your Rust wrapper.
- Your Arrow representation of the transform is already Z-ready (it would
have 12 values instead of 6 in the future where Z is supported).
- Add `Field::new(column::SHAPE, DataType::new_list(DataType::Int64),
false)`, which is the number of values in each of `column::DIMS`, in the same
order. I may be reading it wrong but I think you currently have to peek into
the first band for this. I think it is clearer to keep the spatial source of
truth at the raster level and then validate every band against that (the
transform and the height/width are very closely related to each other and I
think having them at the same level makes sense). Also having a zero-band
raster is surprisingly useful (e.g., gdal uses this as a way to specify a
target grid to use for the result of an operation like warp).
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