This document discusses preparations for new GIS features in MySQL 8.0. It provides an overview of GIS basics like geometries and spatial reference systems. In MySQL 8.0, the world will be able to be flat or ellipsoidal, and operations on geometries in geographic spatial reference systems will use geographic calculations. The document recommends using the correct spatial reference system IDs now, longitude-latitude axis ordering, and following development of MySQL 8.0 GIS features.

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MySQL 8.0: GIS — Are you ready?
Norvald H. Ryeng
Software Engineer
Pre-FOSDEM MySQL Day 2017

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Agenda
GIS basics
What's new in MySQL 8.0?
What can I do now to prepare for what's
coming?
1
2
3
4
5
6
7

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

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GIS basics: Geometries (= geometric objects)
● Geometry
– Point
– LineString
– Polygon
– GeometryCollection
● MultiPoint
● MultiLineString
● MultiPolygon

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GIS basics: Spatial reference systems
SRID 0 Projected SRS Geographic SRS
Cartesian SRS
5.7 8.0

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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)

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

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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

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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

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

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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)

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✓✓
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
●

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POINT(50.8267054 4.3980435)

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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

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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)

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✓
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

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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]⟨

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Prepare now: Axis direction
● It probably won't affect you
● But do it right still!
✓

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

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✓✓
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/

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