MySQL 8.0: GIS — Are you ready?

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MySQL 8.0: GIS — Are you ready?

Norvald H. RyengSoftware Engineer

Pre-FOSDEM MySQL Day 2017

4Copyright © 2017 Oracle and/or its affiliates. All rights reserved.

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AgendaGIS basics

What's new in MySQL 8.0?

What can I do now to prepare for what's coming?

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“The early days of GIS were very lonely. No-one knew what it meant.”— Roger Tomlinson, “Father of GIS”


GIS basics: Geometries (= geometric objects)● Geometry

– Point

– LineString

– Polygon

– GeometryCollection

● MultiPoint

● MultiLineString

● MultiPolygon


GIS basics: Spatial reference systems

SRID 0 Projected SRS Geographic SRS

Cartesian SRS

5.7 8.0


GIS basics: Spatial reference systems● Each SRS has a unique spatial reference system ID (SRID)

– Numeric identifier

– No formal standard/catalog of SRIDs

– De facto standard: EPSG Dataset● 4326 = WGS 84 (“GPS coordinates”)

● 3857 = WGS 84 / World Mercator (“Web Mercator”)

● A property of each geometry

● Mixing geometries in different SRIDs in one computation doesn't make sense and will raise an error (also in 5.7)


“Geography is just physics slowed down, with a couple of trees stuck in it.”— Terry Pratchett in The Last Continent


What's new in MySQL 8.0● Geography

– Earth is round(ish)

– Lines are not straight

– The coordinate system wraps: -180, 180]⟨● Spatial reference systems

– Most are still flat (projections)

– Geographic SRSs will affect the result of most computations


5.7● The world is flat

● The world is infinite

● Axes are unitless

● Axes are orthogonal

● Axis order is irrelevant

● Axis direction is irrelevant

8.0● The world can be flat or ellipsoidal

● Geographic coordinate systems wrap around

● Axes have units

● Geographic axes are not orthogonal

● Geographic axis order matters

● Axis direction may be relevant

Copyright © 2017 Oracle and/or its affiliates. All rights reserved.

What can I do now to prepare for what's coming?


Cartesian vs. geographic● Operations on geometries in geographic SRSs will be computed in

geographic SRSs

● How do I know which SRS my geometries are in?

– SELECT ST_SRID(geometry);

– MySQL uses EPSG codes as SRIDs

● http://www.epsg-registry.org/

● Changing SRID in 5.7 is a bit complicated: ST_GeomFromWKB(ST_AsBinary(geometry), srid)

– In 8.0: ST_SRID(geometry, srid)


✓✓Prepare now: Use the right SRID● If you know your data is in a projected SRS, use the correct SRID

– No surprises when upgrading to 8.0

– Semantically correct, carries metadata about units, etc.

● If your data is in a geographic SRS and you know what you're doing, use the correct SRS or SRID 0

– SRID 0 will give you no surprises when upgrading to 8.0

– Geographic SRSs will affect query results

● If you're unsure which SRS/SRID to use, use SRID 0

– No surprises when upgrading to 8.0

– Makes no claim about the SRS except that it's flat

●


POINT(50.8267054 4.3980435)


Longitude and latitude … or latitude and longitude● The “normal” order is latitude first, longitude second

… except in GIS

● Many GIS applications assume longitude-latitude

● ISO and the Open Geospatial Consortium have agreed

– Always use the order specified for the SRS

– Software packages are still trying to adapt

● All geographic SRSs in the EPSG Dataset define latitude-longitude ordering

● MySQL uses the EPSG Dataset


Axis order in MySQL● Stored as X=longitude, Y=latitude on disk

– Expected by ST_Distance_Sphere and GeoJSON functions in 5.7

8.0

● Import/export functions will let you choose geographic axis order

– Default: SRS defined (predefined SRSs: latitude-longitude)

– ST_GeomFromText('POINT(1 2)', 4326, 'axis-order=long-lat')

● Function to swap coordinates: ST_SwapXY(geometry)


✓Prepare now: Axis order● If you store angular coordinates, use X=longitude and

Y=latitude

– Not necessary to swap coordinates in 8.0

– Think carefully about the choice of SRID

– Beware of changes in computations in 8.0

● Import/export in SRID 0 is always X first, Y second

http://www.epsg-registry.org/


Axis direction● Defined in the SRS

● Doesn't matter on an abstract Cartesian plane (SRID 0)

● Matters on georeferenced planes (projections)

– But doesn't affect computations

● Matters in geographic SRSs

– But doesn't affect computations

– May affect results if the meridian is not through Greenwich● Coercion to -180, 180]⟨


Prepare now: Axis direction● It probably won't affect you

● But do it right still! ✓


“GIS is a form of digital mapping technology. Kind of like Google Earth, but better.”— Arnold Schwarzenegger, Governor of California


✓✓Prepare now● Think through your use of SRIDs

– Use SRID 0 if you're unsure

● Use longitude-latitude ordering in 5.7

– But remember that import and export functions follow SRS defined axis order in 8.0

● Think through axis directions

● Follow the progress of MySQL 8.0 GIS development at http://www.mysqlserverteam.com/

MySQL 8.0: GIS — Are you ready?

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