paleolimbot commented on code in PR #240: URL: https://github.com/apache/parquet-format/pull/240#discussion_r1920531034
########## Geospatial.md: ########## @@ -0,0 +1,151 @@ +<!-- + - Licensed to the Apache Software Foundation (ASF) under one + - or more contributor license agreements. See the NOTICE file + - distributed with this work for additional information + - regarding copyright ownership. The ASF licenses this file + - to you under the Apache License, Version 2.0 (the + - "License"); you may not use this file except in compliance + - with the License. You may obtain a copy of the License at + - + - http://www.apache.org/licenses/LICENSE-2.0 + - + - Unless required by applicable law or agreed to in writing, + - software distributed under the License is distributed on an + - "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY + - KIND, either express or implied. See the License for the + - specific language governing permissions and limitations + - under the License. + --> + +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 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 objects must be stored in longitude, +latitude based on the WGS84 datum. + +Custom CRS can be specified by following attributes: +* `crs`: a CRS text representation. If unset, the CRS defaults to `"OGC:CRS84"`. +* `crs_encoding`: a standard encoding used to represent the CRS text. If unset, + `crs` can be arbitrary string. + +For maximum interoperability of a custom CRS, it is recommended to provide +the CRS text with a standard encoding. Supported CRS encodings are: +* `SRID`: [Spatial reference identifier][srid], CRS text is the identifier itself. +* `PROJJSON`: [PROJJSON][projjson], CRS text is the PROJJSON string. + +For example, a writer may write a PROJJSON representation of [OGC:CRS84][ogc-crs84] +to the `crs` field and set the `crs_encoding` field to `"PROJJSON"`. + +[srid]: https://en.wikipedia.org/wiki/Spatial_reference_system#Identifier +[projjson]: https://proj.org/en/stable/specifications/projjson.html +[ogc-crs84]: https://github.com/opengeospatial/geoparquet/blob/main/format-specs/geoparquet.md#ogccrs84-details + +## 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`: Geometry features in the WKB format with linear/planar edges interpolation. See [Geometry](LogicalTypes.md#geometry) +* `GEOGRAPHY`: Geography features in the WKB format with an explicit (non-linear/non-planar) edges interpolation algorithm. See [Geography](LogicalTypes.md#geography) + +# Statistics + +`GeometryStatistics` 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 [Geometry +Types](#geometry-types) that are described below in detail. + +## Bounding Box + +A geometry has at least two coordinate dimensions: X and Y for 2D coordinates +of each point. A geometry can optionally have Z and / or M values associated +with each point in the geometry. + +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 geometry 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 geometries. + +For the X and Y values only, (xmin/ymin) may be greater than (xmax/ymax). In this +X case, an object in this bounding box may match if it contains an X such that +`x >= xmin` OR `x <= xmax`, and in this Y case if `y >= ymin` OR `y <= ymax`. +In geographic terminology, the concepts of `xmin`, `xmax`, `ymin`, and `ymax` +are also known as `westernmost`, `easternmost`, `northernmost` and `southernmost`. Review Comment: ```suggestion are also known as `westernmost`, `easternmost`, `southernmost` and `northernmost`, respectively. ``` ########## src/main/thrift/parquet.thrift: ########## @@ -417,6 +498,7 @@ 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 Review Comment: ```suggestion 17: GeometryType GEOMETRY // no compatible ConvertedType 18: GeographyType GEOGRAPHY // no compatible ConvertedType ``` Maybe? -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. 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