diff --git a/Geospatial.md b/Geospatial.md new file mode 100644 index 00000000..4be4a38e --- /dev/null +++ b/Geospatial.md @@ -0,0 +1,164 @@ + + +Geospatial Definitions +==== + +This document contains the specification of geospatial types and statistics. + +# Background + +The Geometry and Geography class hierarchy and its Well-Known Text (WKT) and +Well-Known Binary (WKB) serializations (ISO variant supporting XY, XYZ, XYM, +XYZM) are defined by [OpenGIS Implementation Specification for Geographic +information - Simple feature access - Part 1: Common architecture][sfa-part1], +from [OGC(Open Geospatial Consortium)][ogc]. + +The version of the OGC standard first used here is 1.2.1, but future versions +may also be used if the WKB representation remains wire-compatible. + +[sfa-part1]: https://portal.ogc.org/files/?artifact_id=25355 +[ogc]: https://www.ogc.org/standard/sfa/ + +## Coordinate Reference System + +Coordinate Reference System (CRS) is a mapping of how coordinates refer to +locations on Earth. + +The default CRS `OGC:CRS84` means that the geospatial features must be stored +in the order of longitude/latitude based on the WGS84 datum. + +Custom CRS can be specified by a string value. It is recommended to use an +identifier-based approach like [Spatial reference identifier][srid]. + +For geographic CRS, longitudes are bound by [-180, 180] and latitudes are bound +by [-90, 90]. + +[srid]: https://en.wikipedia.org/wiki/Spatial_reference_system#Identifier + +## Edge Interpolation Algorithm + +An algorithm for interpolating edges, and is one of the following values: + +* `spherical`: edges are interpolated as geodesics on a sphere. +* `vincenty`: [https://en.wikipedia.org/wiki/Vincenty%27s_formulae](https://en.wikipedia.org/wiki/Vincenty%27s_formulae) +* `thomas`: Thomas, Paul D. Spheroidal geodesics, reference systems, & local geometry. US Naval Oceanographic Office, 1970. +* `andoyer`: Thomas, Paul D. Mathematical models for navigation systems. US Naval Oceanographic Office, 1965. +* `karney`: [Karney, Charles FF. "Algorithms for geodesics." Journal of Geodesy 87 (2013): 43-55](https://link.springer.com/content/pdf/10.1007/s00190-012-0578-z.pdf), and [GeographicLib](https://geographiclib.sourceforge.io/) + +# Logical Types + +Two geospatial logical type annotations are supported: +* `GEOMETRY`: geospatial features in the WKB format with linear/planar edges interpolation. See [Geometry](LogicalTypes.md#geometry) +* `GEOGRAPHY`: geospatial features in the WKB format with an explicit (non-linear/non-planar) edges interpolation algorithm. See [Geography](LogicalTypes.md#geography) + +# Statistics + +`GeospatialStatistics` is a struct specific for `GEOMETRY` and `GEOGRAPHY` +logical types to store statistics of a column chunk. It is an optional field in +the `ColumnMetaData` and contains [Bounding Box](#bounding-box) and [Geospatial +Types](#geospatial-types) that are described below in detail. + +## Bounding Box + +A geospatial instance has at least two coordinate dimensions: X and Y for 2D +coordinates of each point. Please note that X is longitude/easting and Y is +latitude/northing. A geospatial instance can optionally have Z and/or M values +associated with each point. + +The Z values introduce the third dimension coordinate. Usually they are used to +indicate the height, or elevation. + +M values are an opportunity for a geospatial instance to express a fourth +dimension as a coordinate value. These values can be used as a linear reference +value (e.g., highway milepost value), a timestamp, or some other value as defined +by the CRS. + +Bounding box is defined as the thrift struct below in the representation of +min/max value pair of coordinates from each axis. Note that X and Y Values are +always present. Z and M are omitted for 2D geospatial instances. + +For the X values only, xmin may be greater than xmax. In this case, an object +in this bounding box may match if it contains an X such that `x >= xmin` OR +`x <= xmax`. This wraparound occurs only when the corresponding bounding box +crosses the antimeridian line. In geographic terminology, the concepts of `xmin`, +`xmax`, `ymin`, and `ymax` are also known as `westernmost`, `easternmost`, +`southernmost` and `northernmost`, respectively. + +For `GEOGRAPHY` types, X and Y values are restricted to the canonical ranges of +[-180, 180] for X and [-90, 90] for Y. + +```thrift +struct BoundingBox { + 1: required double xmin; + 2: required double xmax; + 3: required double ymin; + 4: required double ymax; + 5: optional double zmin; + 6: optional double zmax; + 7: optional double mmin; + 8: optional double mmax; +} +``` + +## Geospatial Types + +A list of geospatial types from all instances in the `GEOMETRY` or `GEOGRAPHY` +column, or an empty list if they are not known. + +This is borrowed from [geometry_types of GeoParquet][geometry-types] except that +values in the list are [WKB (ISO-variant) integer codes][wkb-integer-code]. +Table below shows the most common geospatial types and their codes: + +| Type | XY | XYZ | XYM | XYZM | +| :----------------- | :--- | :--- | :--- | :--: | +| Point | 0001 | 1001 | 2001 | 3001 | +| LineString | 0002 | 1002 | 2002 | 3002 | +| Polygon | 0003 | 1003 | 2003 | 3003 | +| MultiPoint | 0004 | 1004 | 2004 | 3004 | +| MultiLineString | 0005 | 1005 | 2005 | 3005 | +| MultiPolygon | 0006 | 1006 | 2006 | 3006 | +| GeometryCollection | 0007 | 1007 | 2007 | 3007 | + +In addition, the following rules are applied: +- A list of multiple values indicates that multiple geospatial types are present (e.g. `[0003, 0006]`). +- An empty array explicitly signals that the geospatial types are not known. +- The geospatial types in the list must be unique (e.g. `[0001, 0001]` is not valid). + +[geometry-types]: https://github.com/opengeospatial/geoparquet/blob/v1.1.0/format-specs/geoparquet.md?plain=1#L159 +[wkb-integer-code]: https://en.wikipedia.org/wiki/Well-known_text_representation_of_geometry#Well-known_binary + +# CRS Customization + +CRS is represented as a string value. Writer and reader implementations are +responsible for serializing and deserializing the CRS, respectively. + +As a convention to maximize the interoperability, custom CRS values can be +specified by a string of the format `type:identifier`, where `type` is one of +the following values: + +* `srid`: [Spatial reference identifier](https://en.wikipedia.org/wiki/Spatial_reference_system#Identifier), `identifier` is the SRID itself. +* `projjson`: [PROJJSON](https://proj.org/en/stable/specifications/projjson.html), `identifier` is the name of a table property or a file property where the projjson string is stored. + +# Coordinate axis order + +The axis order of the coordinates in WKB and bounding box stored in Parquet +follows the de facto standard for axis order in WKB and is therefore always +(x, y) where x is easting or longitude and y is northing or latitude. This +ordering explicitly overrides the axis order as specified in the CRS. diff --git a/LogicalTypes.md b/LogicalTypes.md index 3aa5ceb9..4667453b 100644 --- a/LogicalTypes.md +++ b/LogicalTypes.md @@ -599,6 +599,39 @@ optional group variant_shredded (VARIANT) { } ``` +### GEOMETRY + +`GEOMETRY` is used for geospatial features in the Well-Known Binary (WKB) format +with linear/planar edges interpolation. It must annotate a `BYTE_ARRAY` +primitive type. See [Geospatial.md](Geospatial.md) for more detail. + +The type has only one type parameter: +- `crs`: An optional string value for CRS. If unset, the CRS defaults to + `"OGC:CRS84"`, which means that the geometries must be stored in longitude, + latitude based on the WGS84 datum. + +The sort order used for `GEOMETRY` is undefined. When writing data, no min/max +statistics should be saved for this type and if such non-compliant statistics +are found during reading, they must be ignored. + +### GEOGRAPHY + +`GEOGRAPHY` is used for geospatial features in the WKB format with an explicit +(non-linear/non-planar) edges interpolation algorithm. It must annotate a +`BYTE_ARRAY` primitive type. See [Geospatial.md](Geospatial.md) for more detail. + +The type has two type parameters: +- `crs`: An optional string value for CRS. It must be a geographic CRS, where + longitudes are bound by [-180, 180] and latitudes are bound by [-90, 90]. + If unset, the CRS defaults to `"OGC:CRS84"`. +- `algorithm`: An optional enum value to describes the edge interpolation + algorithm. Supported values are: `SPHERICAL`, `VINCENTY`, `THOMAS`, `ANDOYER`, + `KARNEY`. If unset, the algorithm defaults to `SPHERICAL`. + +The sort order used for `GEOGRAPHY` is undefined. When writing data, no min/max +statistics should be saved for this type and if such non-compliant statistics +are found during reading, they must be ignored. + ## Nested Types This section specifies how `LIST` and `MAP` can be used to encode nested types diff --git a/src/main/thrift/parquet.thrift b/src/main/thrift/parquet.thrift index 5d4431d9..ee701aa9 100644 --- a/src/main/thrift/parquet.thrift +++ b/src/main/thrift/parquet.thrift @@ -237,6 +237,29 @@ struct SizeStatistics { 3: optional list definition_level_histogram; } +/** + * Bounding box for GEOMETRY or GEOGRAPHY type in the representation of min/max + * value pair of coordinates from each axis. + */ +struct BoundingBox { + 1: required double xmin; + 2: required double xmax; + 3: required double ymin; + 4: required double ymax; + 5: optional double zmin; + 6: optional double zmax; + 7: optional double mmin; + 8: optional double mmax; +} + +/** Statistics specific to Geometry and Geography logical types */ +struct GeospatialStatistics { + /** A bounding box of geospatial instances */ + 1: optional BoundingBox bbox; + /** Geospatial type codes of all instances, or an empty list if not known */ + 2: optional list geospatial_types; +} + /** * Statistics per row group and per page * All fields are optional. @@ -386,6 +409,55 @@ struct BsonType { struct VariantType { } +/** Edge interpolation algorithm for Geography logical type */ +enum EdgeInterpolationAlgorithm { + SPHERICAL = 0; + VINCENTY = 1; + THOMAS = 2; + ANDOYER = 3; + KARNEY = 4; +} + +/** + * Embedded Geometry logical type annotation + * + * Geospatial features in the Well-Known Binary (WKB) format and edges interpolation + * is always linear/planar. + * + * A custom CRS can be set by the crs field. If unset, it defaults to "OGC:CRS84", + * which means that the geometries must be stored in longitude, latitude based on + * the WGS84 datum. + * + * Allowed for physical type: BYTE_ARRAY. + * + * See Geospatial.md for details. + */ +struct GeometryType { + 1: optional string crs; +} + +/** + * Embedded Geography logical type annotation + * + * Geospatial features in the WKB format with an explicit (non-linear/non-planar) + * edges interpolation algorithm. + * + * A custom geographic CRS can be set by the crs field, where longitudes are + * bound by [-180, 180] and latitudes are bound by [-90, 90]. If unset, the CRS + * defaults to "OGC:CRS84". + * + * An optional algorithm can be set to correctly interpret edges interpolation + * of the geometries. If unset, the algorithm defaults to SPHERICAL. + * + * Allowed for physical type: BYTE_ARRAY. + * + * See Geospatial.md for details. + */ +struct GeographyType { + 1: optional string crs; + 2: optional EdgeInterpolationAlgorithm algorithm; +} + /** * LogicalType annotations to replace ConvertedType. * @@ -417,6 +489,8 @@ union LogicalType { 14: UUIDType UUID // no compatible ConvertedType 15: Float16Type FLOAT16 // no compatible ConvertedType 16: VariantType VARIANT // no compatible ConvertedType + 17: GeometryType GEOMETRY // no compatible ConvertedType + 18: GeographyType GEOGRAPHY // no compatible ConvertedType } /** @@ -857,6 +931,9 @@ struct ColumnMetaData { * filter pushdown. */ 16: optional SizeStatistics size_statistics; + + /** Optional statistics specific for Geometry and Geography logical types */ + 17: optional GeospatialStatistics geospatial_statistics; } struct EncryptionWithFooterKey { @@ -988,6 +1065,8 @@ union ColumnOrder { * LIST - undefined * MAP - undefined * VARIANT - undefined + * GEOMETRY - undefined + * GEOGRAPHY - undefined * * In the absence of logical types, the sort order is determined by the physical type: * BOOLEAN - false, true