RE: [MI-L] Overlap analysis - Oracle tables

Llewellyn, David Sun, 26 Mar 2006 17:16:51 -0800

Title: Overlap analysis - Oracle tables

Peter,

If I use CartesianArea() in MapInfo I get -1.

I guess this is MapInfo’s way of telling me that there is really no such thing as cartesian area on the surface of a spheroid.

For testing purposes I created two square polygons in MapInfo of 1km sides. The polygons overlap, with a corner of one at the centre of the other, so the overlap is theoretically one quarter.

One polygon is in Table ‘Test1’, the other in Table ‘Test2’.

I get the following results:

MapInfo Area Oracle Area

--------------- -------------

Test1 0.999969 0.997368877

Test2 0.999938 0.997338099

Overlap 0.249961 0.24930843

As you can see they differ by that same 0.9974 factor.

I was thinking that I may need to use the ‘other’ format for area in Oracle Spatial:

SDO_GEOM.SDO_AREA(

geom IN MDSYS.SDO_GEOMETRY,

tol IN NUMBER

[, unit IN VARCHAR2]

) RETURN NUMBER;

I’ll try that out today.

Cheers (and thanks for your interest)

David Llewellyn

-----Original Message-----
From: Peter Horsbøll Møller [mailto:[EMAIL PROTECTED]
Sent: Friday, 24 March 2006 5:47 PM
To: Llewellyn, David
Cc: [email protected]
Subject: RE: [MI-L] Overlap analysis - Oracle tables

David,

How big is the difference if you use the CartesianArea() function in MapInfo ?

Peter Horsbøll Møller
GIS Developer, MTM
Geographical Information & IT

COWI A/S
Odensevej 95
DK-5260 Odense S.
Denmark

Tel     +45 6311 4900
Direct +45 6311 4908
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Fax     +45 6311 4949
E-mail [EMAIL PROTECTED]
http://www.cowi.dk/gis

From: Llewellyn, David [mailto:[EMAIL PROTECTED]
Sent: Friday, March 24, 2006 3:29 AM
To: Peter Horsbøll Møller
Cc: [email protected]
Subject: RE: [MI-L] Overlap analysis - Oracle tables

Peter,

In the version of Oracle Spatial we are running (9.2.0.6.0) the querytype parameter must be included.

I have tried querytype=JOIN

But the results are still the same.

See the actual query and output below:

1 SELECT A.TRI_NUM, SDO_GEOM.SDO_AREA(SDO_GEOM.SDO_INTERSECTION(A.GEOLOC, B.GEOLOC, 0.005), 0.005, 'unit=SQ_KM') "OLAP"

2 FROM NTDA_REG_QLD A, NTDA_SCH_QLD B

3 WHERE B.TRI_NUM = 'QQ99/9'

4* AND SDO_RELATE(A.GEOLOC, B.GEOLOC, 'mask = ANYINTERACT querytype=JOIN') = 'TRUE'

TRI_NUM OLAP

---------- ----------

QC99/xx .055406902

QC97/yy 21061.2942

QC02/zz .539097535

QC99/pp 1278.13187

The areas above differ from the areas output by MapInfo (using the ‘Area’ function) by a factor of about 0.9974.

Best regards,

David Llewellyn.

-----Original Message-----
From: Peter Horsbøll Møller [mailto:[EMAIL PROTECTED]
Sent: Thursday, 23 March 2006 8:00 PM
To: Llewellyn, David
Subject: RE: [MI-L] Overlap analysis - Oracle tables

Hi David,

Try without the querytype=WINDOW

From: Llewellyn, David [mailto:[EMAIL PROTECTED]
Sent: Thursday, March 23, 2006 2:06 AM
To: Peter Horsbøll Møller
Subject: RE: [MI-L] Overlap analysis - Oracle tables

Thanks for the suggestion Peter,

A useful one. The results however, are the same.

Still, would be interested to know if you come up with anything that might be useful from your course.

From my initial reading, I think the problem might have something to do with the SRID number in the USER_SDO_GEOM_METADATA view (see below).

Unfortunately, my knowledge of Oracel Spatial is still pretty scant, so actually how to update that number is so far a mystery.

Best regards,

David Llewellyn

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