CRS and SVG

Satoru Takagi , SVGWG

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/

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

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.

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)

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

CRSTransformation

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.

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.

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 SystemsMetadata 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.

<?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>

ExampleMap_content A.svg

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/

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-charterSee also SVGWG’s charter

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?

General-purpose functions by CRS

Layering

Gemini2DIllustration

Caption Layer

Marker Layer

Sketch Layer

CRS = “Gemini2DIllustration”

CRS = “Gemini2DIllustration”

CRS = “Gemini2DIllustration”

CRS = “Gemini2DIllustration”

Layering shares a common coordinate system among layers.

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

Tiling (High resolution Graphics)

See also: Microsoft’s Zoomable High-resolution Photoshttp://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.

These functions are important also for GIS and Web Mapping.

Are there any other general-purpose functions which used CRS?