The examination about how to handle coordinate reference systems on SVG.

1. CRS and SVG
Satoru Takagi , SVGWG

2. I am a engineer who have been developing
Geographic Information Systems and Web Mapping
Systems which used SVG for about fifteen years.
Self-introduction
And I am taking charge of the
standardization in SVGWG
mainly concerning Mapping.
Moreover, I was involved also
with de-jure standardization of
GML in Japan, and a
development of the RDF
vocabulary for geospatial
information.
http://svg2.mbsrv.net/devinfo/devkddi/lvl0.1/

3. My interest is fusion of graphics on web and
geographic information.
In particular, it is a map contents as a graphics.
It is because a lot of map contents are on the web.
This document will search for the gap between such
a graphics and geographic information.
The aim of this slide

4. Graphics A
Graphics B
User Coordinate System A User Coordinate System B
Unrelated
Graphic Contents
On mere graphics contents, each contents are usually unrelated. Therefore, these coordinate systems are
also individual and unrelated.
In SVG, such coordinate systems are called User Coordinate System.

5. Coordinate Reference System : EPSG:3857
Geographic Information System A
Geographic Information System B
Geographic Information System C
Geographic Information Systems
for instance
Geographic information systems has CRS. Since common
well known CRS is shared by multiple GIS, we can make
these cooperate, such as layering.
(CRS)

6. Coordinate Reference System : EPSG:3857
Geographic Information Systems
for instance
Even if different CRS are used among GIS, we
can still cooperate by CRS transformation.
EPSG:3995
EPSG:4326
EPSG:326xx
CRS
Transformation

7. Unrelated
User Coordinate System A
User Coordinate System B
User Coordinate System B
Map content A
Map content B
Map content C
Map Contents
On the other hand, there is no concept of CRS on mere
map contents. Since it is a kind of graphics contents
eventually.
Therefore, we cannot make these cooperate.
The map contents by SVG are also in the same
situation basically.

8. Geographic Coordinate Systems Section on SVG1.1
http://www.w3.org/TR/SVG/coords.html#GeographicCoordinates
Meanwhile, there is specification concerning CRS in SVG1.1.
It is the specification for embedding geospatial coordinate system information as metadata into map
contents.
Accordingly, it allows to regard map contents also as geographic information. It could be called one of the
styles of Spatial Data on the Web.

9. User Coordinate System A
User Coordinate System B
User Coordinate System C
Map content A
Map content B
Map content C
svg:transform
svg:transform
svg:transform
Coordinate Reference System : EPSG:3857
Geographic coordinate Systems
Metadata on SVG1.1
for instance
That metadata is constituted by CRS of the source
geographic information used on the map generation process,
and its coordinate transformation factor to User Coordinate
System of the map content.

10. <?xml version="1.0"?>
<svg xmlns="http://www.w3.org/2000/svg" version="1.1"
width="100" height="100" viewBox="0 0 1000 1000">
<metadata>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:crs="http://www.ogc.org/crs"
xmlns:svg="http://www.w3.org/2000/svg">
<rdf:Description rdf:about="">
<!-- The Coordinate Reference System is described
through a URI. -->
<crs:CoordinateReferenceSystem
svg:transform="rotate(-90)"
rdf:resource="urn:ogc:def:crs:EPSG::3857 "/>
</rdf:Description>
</rdf:RDF>
</metadata>
<!-- The actual map content -->
</svg>
Example
Map_content A.svg

11. ISSUE
• It is too flexible and complicated by RDF/XML.
• Browsers provides no functions which used it,
since it is mere metadata.
• It is still future that SVG is widely used for map
contents.
Nobody is using it.
That specification will be removed in SVG2.
And it is under re-examination. The person in charge is me.
https://svgwg.org/svg2-draft/
https://svgwg.org/specs/transform/

12. Our Directivity of re-examination
In order to promote SVG map contents with CRS,
• Markup should be simpler.
• Browsers should have certain convenient native
functions using CRS.
In order to promote Browser implementations,
• The concept of CRS should be generalized.
• Such functions using CRS should be general-purpose
not only for spatial information and mapping.
Because standardization of multiuse functions is welcomed for web browsers.
http://www.w3.org/Graphics/SVG/2014/new-charter
See also SVGWG’s charter

13. Generalized CRS concept?
My thought:
Generalized CRS is the concept of a certain coordinate
system which multiple contents or systems share.
There may be a variety of shared coordinate systems.
Therefore, it intends that it is declared on a content or
a system so that it may be known by the others what
coordinate system is used.
The coordinate transformation among different CRS is
a extended concept according to a case such as geo-
graphical.
Is it acceptable for geo guys?
Should another name for this concept be attached?

14. General-purpose functions by CRS

15. Layering
Gemini2DIllustration
Caption Layer
Marker Layer
Sketch Layer
CRS = “Gemini2DIllustration”
CRS = “Gemini2DIllustration”
CRS = “Gemini2DIllustration”
CRS = “Gemini2DIllustration”
Layering shares a common coordinate system among
layers.

16. CRS = “ZoomableWireFrameIllustration”
CRS = “ZoomableWireFrameIllustration”
CRS = “ZoomableWireFrameIllustration”
CRS = “ZoomableWireFrameIllustration”
Hi Res. Content
Low Res. Content
Medium Res. Content
The level of detail function shares a common coordinate
system among contents of each resolution.
Level of Detail

17. Tiling (High resolution Graphics)
See also: Microsoft’s Zoomable High-resolution Photos
http://www.microsoft.com/web/solutions/zoomit.aspx
Tile1-1 Tile2-1 Tile3-1 Tile4-1
Tile1-2 Tile2-2 Tile3-2 Tile4-2
Tile1-3 Tile2-3 Tile3-3 Tile4-3
Tile1-4 Tile2-4 Tile3-4 Tile4-4
On tiling, each tile graphics share a common coordinate system.

18. These functions are important also for
GIS and Web Mapping.
Are there any other general-purpose
functions which used CRS?