David, A CartesianArea value of -1 is returned
when the corrdinate system is lat/ long. It can only be used with non-lat/
long based tables. You would need to use SphericalArea(Obj, “UnitName”)
to get the numbers. Would be interested in your results in
terms of calculated areas using this function. ------------------------------------------- Robert
Crossley Agtrix
P/L Far
P: 61 2 6680
1309 F: 61 2 6680
5214 Cooparoo
4151 P: 61 7 3843
3363
From:
[EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Llewellyn, David 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----- David, How big is the
difference if you use the CartesianArea() function in MapInfo ? Peter
Horsbøll Møller From:
Llewellyn, David [mailto:[EMAIL PROTECTED] 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----- Hi David, Try without the querytype=WINDOW Peter Horsbøll Møller From: Llewellyn,
David [mailto:[EMAIL PROTECTED] 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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