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c-squares - a new method for representing, querying, displaying and exchanging dataset spatial extents. System concept and development by: Tony Rees Divisional Data Centre CSIRO Marine Research, Australia. some example Metadatabases (Data Directories). + many others -- 100 < 1000?.

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c-squares - a new method for representing, querying, displaying and exchanging dataset spatial extents

System concept and development by:

Tony Rees

Divisional Data Centre

CSIRO Marine Research, Australia


some example Metadatabases (Data Directories)

+ many others -- 100 < 1000? ...

  • Typical features: include searchability by

    • text

    • keywords

    • spatial and time constraints

  • This presentation - focus onspatial searching


--------- data

----- data bounding rectangle (MBR)

--------- search rectangle

current “base level” representation of spatial data coverage in metadata is by bounding box (minimum bounding rectangle, MBR)

  • concept introduced in 1994 (FGDC)

  • used for spatial searching, 1995 onwards

  • still the primary tool for metadata spatial searches


SRTM 8-449 catch data

Catch records - Hoplostethus atlanticus

How well do MBR’s represent spatial data?

(examples from our own metadata system)

MBR actual data locations

Franklin 02/1999 hydrology data


alternatives to MBR’s for representation of data spatial extents ...

  • bounding polygons

  • multiple bounding rectangles

  • defined regions - countries, administrative areas, bio- or geo-regions …

  • circles (centre point + radius)

  • pre-defined path + distance (e.g. along a contour, coastline, satellite path)

  • actual point locations held in the metadata record

  • grid-based system


global grid systems already available ... extents ...

  • International Map of the World (IMW) rectangles (6 x 4 degrees)

  • Marsden Squares (10 x 10 degrees)

  • Maidenhead Squares (2 x 1 degree)

  • WMO (World Meteorological Organisation) Squares (10 x 10 degrees)

  • others ?

  • -- WMO squares eventually chosen for ease of subdivision (base 10) and simple relationship between WMO numbers and lat/long values


3414 extents ...

1400

WMO 10-degree squares notation (part)

(Available via the web in NODC, 1998:World Ocean Database 1998 Documentation)


The “ extents ...c-squares”

concept

c-squares:

Concise Spatial Query and Representation System


same using 0.5 x 0.5 degree c-squares extents ...

data “footprint” using 1 x 1 degree c-squares

“c-squares” principle

data “footprint” using bounding rectangle

actual ship’s track - “Franklin” voyage 10/87


“c-squares” numbering system extents ...

  • each square is numbered according to a globally applicable system based on recursive divisions of WMO (World Meteorological organisation) 10-degree squares, e.g.:

  • 10 degree square: 3414 (= WMO number)

  • 5 degree square: 3414:2

  • 1 degree square: 3414:227

  • 0.5 degree square: 3414:227:4

  • 0.1 degree square: 3414:227:466

  • (etc.)

  • strings of codes represent an individual dataset extent, e.g.

  • 3013:497|3111:468|3111:478|3111:479|3111:488|3111:489|3111:499|3112:122|3112:123|

  • 3112:131|3112:132|3112:134|3112:141|3112:142|3112:143|3112:217|3112:218|3112:219|

  • 3112:226|3112:235|3112:350|3112:351|3112:352|3112:353|3112:360|3112:361|3112:362|

  • 3112:363|3112:370|3112:371|3112:380|3112:381|3112:390|3113:100|3113:101|3113:102|

  • 3113:103|3113:104|3113:205|3113:206|3113:207|3113:216|3113:217|3113:228|3113:238|

  • 3113:239

  • encodes the extent

  • shown in the example:


0.5- and 0.1- degree squares extents ...

Codes have straightforward relationship with lats/longs, mapsheets, etc. ...

e.g.:

1400:458(1-degree square with origin at

45 ºN, 008 ºE)

additional degrees E [00+8] =8

additional degrees N [40+5] = 45

5-degree quadrant, i.e. 3 4

1 2

tens of degrees E (i.e., 00)

tens of degrees N (i.e., 40)

global sector (1=NE, 3=SE, 5=SW, 7=NW)

46

45

44

110 km

10

8

9


“quad tree” -type approach used where numerous adjacent squares are occupied

squares can be “bulked” - example: 3212:*** instead of specifying every 1-degree square within 10 degree square 3212.

This leads to corresponding data reduction, e.g. Australia (at 1-degree resolution) can be described in 343 squares rather than 800:


Example database-level implementation of c-squares for metadata records(e.g. at 1 degree resolution)

(etc.)


Spatial queries using c-squares metadata records

  • c-squares spatial queries simply test whether a text string representing the search box (ideally one or several c-squares) is matched anywhere in the c-squares string …

  • example: - search square 3113:2 will match any c-squares string which includes 3113:2 within it, e.g.:

  • <csquares>

  • 3112:363|3112:370|3112:371|3112:380|3112:381|3112:390|3113:100|3113:101|3113:102|

  • 3113:103|3113:104|3113:205|3113:206|3113:207|3113:216|3113:217|3113:228|3113:238|

  • 3113:239

  • </csquares>

  • hierarchical naming system for c-squares means that finer resolution squares are automatically picked up in any “coarser resolution” search


example search result ... metadata records

(etc.)


Viewing the full metadata record produces ... metadata records

with clickable link to show dataset extent using c-squares:

(etc.)


Base maps for displayed data can be changed at will by the user, e.g.:

(numerous other maps available, sample only shown)


Process invoked for web mapping user, e.g.:

c-squares strings can be sent directly to the CMR c-squares mapper (accessible via the web), e.g. from OBIS (Ocean Biogeographic Information System, USA):

<form action = "http://www.marine.csiro.au/cgi-bin/cs_map.pl" method="post">

<INPUT TYPE="hidden" NAME="csq" VALUE="3215:459:4|3215:459:3|3215:459:4|(etc.)">

<INPUT TYPE="hidden" NAME="title" VALUE="Global Distribution of <i>Raja</i>">

<INPUT TYPE="submit" NAME="submit" VALUE="make map ...">

</form>


c-squares strings are suitable for inclusion as a new metadata element alongside “bounding box”, for example ...

<metadata>

<title>Franklin Voyage FR 10/87 CTD Data</title>

<custodianOrg>CSIRO Marine Research</custodianOrg>

(etc. etc.)

<boundingBox>

<northBoundingCoord>-9.0</northBoundingCoord>

<southBoundingCoord>-19.0</southBoundingCoord>

<westBoundingCoord>117.0</westBoundingCoord>

<eastBoundingCoord>145.8</eastBoundingCoord>

</boundingBox>

<csquares>3111:499:2|3112:390:1|3111:489:3|3112:380:3|3112:380:4|3112:381:1|3111:488:2|3112:381:2|3112:371:3|3111:478:4|3112:370:4|3112:370:1|3111:478:1|3111:479:2|3111:479:1|3112:361:4|3111:468:4|3112:363:3|3112:361:3|3111:467:2|3112:360:2|3112:363:1|3112:362:2|3112:360:1|3112:352:4|3112:352:3|3112:350:4|3112:352:1|3112:351:2|3112:352:2|3112:353:2|3112:353:1</csquares>

(etc.)

… would permit interoperability with both enabled and non-enabled systems


Summary - strengths and weaknesses of c-squares metadata element alongside “bounding box”, for example ...

  • Strengths ...

  • “c-squares” is a concise and flexible method of encoding simple to moderately complex forms

  • automated or manual code entry (and maintenance) is straightforward

  • spatial searching is simple text string matching operation (no GIS involved)

  • “c-squares mapper” utility available via simple web call

  • can be used as adjunct to bounding coordinates searches

  • Weaknesses …

  • some other numbering systems in use (Marsden Squares, Maidenhead Locators) - needs willingness to standardise on a single system for interoperability

  • c-squares are not a fixed multiple of kilometres, miles, etc.

  • strings can become quite long for large, complex regions (e.g. “Pacific Ocean”) - need to be able to incorporate data reduction using “bulk” method


other comments ... metadata element alongside “bounding box”, for example ...

  • “c-squares” notation is language-independent - can be equally useful in English, French, Italian, Japanese … also discipline-independent

  • downwards-scalability of the c-squares notation means that it can be applied to any size region (e.g. local level)

  • equally applicable to both terrestrial and marine data

  • uses established standards for nomenclature, basis already available via the web (e.g. NODC site)


c-squares current and future status... metadata element alongside “bounding box”, for example ...

  • Implemented already in CMR’s “MarLIN” metadata system and “CAAB” taxon dictionary

  • concept is available for implementation in any other agencies’ metadata systems without cost or technology overhead

  • potential to to be recognised as a formal metadata element by relevant user communities / national bodies

  • current CMR c-squares mapper is already accessible for general use

  • c-squares website constructed as a focal point for all c-squares related materials - including:

    • initial c-squares specification

    • connection information to the c-squares mapper

    • sample PL/SQL code (to convert lat/long pairs to c-squares)

    • on-line lat/long - to - c-square converter

    • example c-squares-enabled metadata records, and more


  • Acknowledgements … metadata element alongside “bounding box”, for example ...

  • Miroslaw Ryba and other CMR staff for assistance with constructing the c-squares mapper and general feedback

  • “Blue Pages” Marine and Coastal Data Directory (MCDD) for the notation for subdividing WMO squares

  • Martin Dix (CSIRO Atmospheric Research) and NOAA “Globe” Project for base maps as used in the mapper (used by permission)

Questions, comments?

website: http://www.marine.csiro.au/csquares/

(NB: handout available at this meeting)

My email: [email protected]


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