MySQL 8.0: GIS — Are you ready?

Copyright © 2017 Oracle and/or its affiliates. All rights reserved.
MySQL 8.0: GIS — Are you ready?
Norvald H. Ryeng
Software Engineer
Pre-FOSDEM MySQL Day 2017

4Copyright © 2017 Oracle and/or its affiliates. All rights reserved.
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The following is intended to outline our general product direction. It is intended for
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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

“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

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?

MySQL 8.0: GIS — Are you ready?

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