Www.cmar.csiro.au Rapid spatial indexing and web mapping using the “c-squares” global grid Tony Rees Manager, Divisional Data Centre 23 March 2007 CSIRO

www.cmar.csiro.au

Rapid spatial indexing and web mapping using the “c-squares” global grid

Tony Rees

Manager, Divisional Data Centre

23 March 2007

CSIRO Marine and Atmospheric Research

Introduction

• Web mapping – here considered to be dynamic map generation and return in response to an internet request (OGC-compliant requests and responses are a subset of these)

• Slightly different / extended concept – web plotting of user-supplied data – subject of this talk

• Data may be supplied by human user, or (more typically) a client application, over the web for real-time plotting

• Example to be discussed is the “c-squares mapper” – developed at CMAR and in use for last 5+ years

• “C-squares” are units of spatial indexing – data format used as mapper input (however, underlying mechanics may be hidden from the human user).

Example usage – CMAR “CAAB” database http://www.cmar.csiro.au/caab/

Example usage – CMAR “CAAB” database http://www.cmar.csiro.au/caab/

Behind the scenes – set of c-square codes:

Each c-square code is a global grid cell identifier.

Regional and Global grids

Regional grid example: British Isles…

3 problems for large scale use:

(1) Grid does not align with lat-lon graticule


Regional grid example: British Isles…

3 problems for large scale use:

(1) Grid does not align with lat-lon graticule

(2) No single grid covers whole target area – problems where grids meet

(3) Some outlying portions have no grid coverage at all (e.g. Channel Is.)


Global grids better, e.g. WMO 10 x 10 deg. squares:


In our region:

The “c-squares” global grid

• C-squares = “Concise Spatial Query and Representation System” – now 5 years old (initial code, mapper written Jan ’02)

• Creates hierarchical subdivisions of WMO 10 x 10 deg. squares, e.g.

3414 = 10 deg. square

3414:1 = 5 deg. square within square 3414

3414:104 = 1 deg. square within square 3414:1

3414:104:3 = 0.5 deg. square within square 3414:104

(etc., etc.)

Note the “telephone number” analogy, i.e. country => area => sub-area => sub-sub-area etc.

The “c-squares” global grid

Example squares + IDs

3414:227(1 deg. square)

3414:227:2(0.5 deg. square)

3414:227:209(0.1 deg. square)

Spatial indexing using c-squares

Sample uses:

Multi-point data set(NB, can be 1 - many points in a square)


Predicted marine species range (~= polygon)

Sample uses:


Gridded data (density per cell)

Sample uses:

The c-squares mapper

Example code (as HTML page): - a few of many options shown

<html><body><form action = "http://www.obis.org.au/cgi-bin/cs_map.pl" method = "POST" /><input type = "hidden" name = "csq" value = "3414:100:1|3414:100:2|3414:100:3" /><input type = "hidden" name = "color" value = "FF0000" /><input type = "hidden" name = "fill" value = "Y" /><input type = "hidden" name = "map" value = "" /><input type = "submit" name = "submit" value = "Get map..." /></form></body</html>

Websites to see examples:CAAB – http://www.cmar.csiro.au/caab/MarLIN – http://www.cmar.csiro.au/marlin/AquaMaps – http://www.aquamaps.org/OBIS – http://www.iobis.org/









Sample usage

MarLIN – metadata catalogue for CSIRO Marine and Atmospheric Research – www.cmar.csiro.au/marlin/

Behind the scenes…

Sample usage

AquaMaps – predicted marine species distributions – www.aquamaps.org

Sample usage

OBIS – Ocean Biogeographic Information System – www.iobis.org/

OBIS data – “all vertebrates” (6 million records, 41,000 squares) ... plotting time 16 / 25 secs (std. vs. large size map)

Sample usage

OBIS species page – “wandering albatross”

Sample usage

OBIS data – “wandering albatross” (970 records, 530 squares) ...

Sample usage

Sample usage

Current max. zoom(from “globe views”)

Sample usage

Some plotting times compared (Duke University Geospatial Lab, unpubl, Mar 2006, plus present data)

Plotted data ArcIMS MapServer Google Earth c-squares mapper *

1,200 points 4 secs. 6 secs. 4 secs. 3-10 secs.

* - present data (not in Duke Univ. study). Longer times are for “large world” base maps.

NB, new CSQ mapper “globe views” take only 2-3 secs each time after initial map generation

Sample usage







Sample usage





90,000 points 14 secs. 18 secs. not stated 25-45 secs.



Sample usage






206,000 points 55 secs. 19 secs. > 5 mins. 3-6 mins.



Sample usage






206,000 points 55 secs. 19 secs. > 5 mins. 3-6 mins.

1,090,000 points 58 secs. 20 secs. not possible not possible **



** c-squares mapper can plot millions of points in practice after data reduction (e.g. OBIS “vertebrates” example: 6 m records / 41,000 squares / 25 secs or less to plot)

Some future gazing…

SWOT Analysis – strengths, weaknesses, opportunities, threats?

STRENGTHS• Low / no cost solution for basic spatial indexing and search, and “entry-level” web mapping

• Easy to install in non-GIS enabled systems (e.g. metadata catalogues, text documents, standard databases)

• Good fit with grid-based data, multi-point data

• Good for data reduction (e.g. many points, fewer squares)

• No date line problems, also OK with polar data (although indexing is least efficient at poles)

• Remote mapper, no dedicated client-side software, plugins, etc. needed (cf. Google Earth, desktop GIS)



WEAKNESSES• “Jaggies” when representing curves, polylines, polygons

• Large regions require a lot of squares to be processed (slower mapping)

• Spatial queries are approximations (2 features may share the same square, but not quite intersect)

• Squares are not equal-area (latter may be preferred for some purposes)

• Mapper not as fully featured as true web mapping solution; limited zoom, mostly medium / large scale physical backdrops at this time

• No current integration with OGC standards



THREATS• True GIS offers more features / precision, may be needed by many users – if not now, eventually

• Other remote web data plotting solutions have arrived since 2002 (some with more features, better zoom/pan, etc.)

• Google Earth offers great functionality, becoming a “de facto” standard for some types of data presentation

• Mapper development is resources-limited, may lead to being outclassed eventually



OPPORTUNITIES• Further development of c-squares mapper (including open source community, remote installation administrators)

• Additional mapper installations around the world coming on line (today AUS + GER + SWE; USA soon)

• OBIS and other “power users” are providing useful exposure and load testing for the system, also user feedback e.g. desired features

• May be possible to integrate with OGC Web Mapping standards (how…?)

• Maybe keep indexing method, use different mapping solution (provide data as polygons in GML or similar, to a more sophisticated mapper or web map client)

Resources availableC-squares initial published description (Mar 2003) – “Oceanography” vol. 16 (1)

Resources availableC-squares website at CMAR: http://www.cmar.csiro.au/csquares/ (sample page)

Resources availableC-squares SourceForge site: http://csquares.sourceforge.net/

Resources availableC-squares on wikipedia: http://en.wikipedia.org/wiki/C-squares

Thank you!

Questions, comments invited…

Acknowledgements: Miroslaw Ryba, Philip Bohm [CMAR] (programming assistance); GD (graphics routine for the basic plotting); Xplanet (rendering engine for the “Globe Views”).

www.cmar.csiro.au

Thank You

Contact

Name: Tony ReesTitle: Data Centre ManagerPhone: 03 6232 5318Email: [email protected]: www.cmar.csiro.au/datacentre

Contact CSIRO

Phone: 1300 363 400+61 3 9545 2176Email: [email protected]: www.csiro.au

Documents

Www.cmar.csiro.au Rapid spatial indexing and web mapping using the “c-squares” global grid Tony Rees Manager, Divisional Data Centre 23 March 2007 CSIRO