Re: Oracle Spatial Attributes

From: Zaki Kashevarov <zaki_kashevarov_at_lti.co.il>
Date: Sat, 21 Feb 2004 20:12:20 +0200
Message-ID: <40379fb0@news.barak.net.il>

Just want to say something about precision with Oracle Spatial: Tolerance is not the same as precision, tolerance is used when oracle determines intersection and other comparison operations. Precision is how the data is actually stored.

Oracle Spatial stores the points in a varray of Number data types. Because the NUMBER in spatial has no specified precision if can (and will) store up to 36 digits.
This might be a big problem as far as storage is concerned, since oracle actually stores the significant digits.

for example 97.333333333333333333333333333 takes up 16(!!!) bytes in oracle

spatial (for each coordinate), whereas 97.33333 takes only 5 bytes

select vsize(97.333333333333333333333333333) from dual

So if your data came from a floating point calculation (97 1/3 in this example), you should truncate the data to a suitable length before loading it into oracle, otherwise it might take 3-4 times as much space, takes 3-4 times as long to read, etc... it has no benefits.

Regards,
Zaki Kashevarov,
zaki_kashevarov_at_lti.co.il
Do not email me, I will not respond

"Hans Forbrich" <hforbric_at_yahoo.net> wrote in message news:6J8Zb.26134$n17.21075_at_clgrps13...
> FinnE wrote:
> > Hans Forbrich <hforbric_at_yahoo.net> wrote in message
news:<s84Zb.30295$D_5.9646_at_edtnps84>...
> >
> >>FinnE wrote:
> >>
> >>>Is it possible to have multiple spatial attributes in a single
> >>>database record in Oracle9i or higher?
> >>
> >>Yes.
> >>
> >>Some orgs use this fact to have high/med/low resolution point
> >>information in a table allowing the front-end app to switch and chose
> >>the appropriate amount of data to transfer.
> >>
> >><elabortion>
> >>What you refer to as 'Spatial attributes' are object types. You can
> >>have any number in a table and each 'appears' as a column.
> >>
> >>Quick def of the spatial object: There are 5 fields
> >>- general type of data indicator,
> >>- coord-system_id (if using projected coord system),
> >>- single point coords (if type indicates it's only a point),
> >>- a list for the 2D/3D/(+added info such as LRS) data points (generally
> >>counter-clockwise),
> >>- a list that indicates at which point gives a new data definition
> >>(polygon starts here, curve starts here, etc.)
> >>
> >><more info source>
> >>There are a number of excellent tutorials in Oracle's OnLine library at
> >>http://Education.oracle.com
> >></more info source>
> >></elabortion>
> >>
> >>HTH
> >>/Hans
> >>
> >>(BTW - no need to cross-post)
> >
> >
> > Where in the oracle documentation does it give you that information?
> > Also do you know - to what precision can Oracle Spatical store arcsec?
> > Erin

> In the Spatial documentation. To get to the docco ...

> http://docs.oracle.com
> >> the database version you're working on
> >> 'View Library' link
> >> 'List of Books' link
> >> Spatial User's Guide and Reference (about 60% down the page)

> The precision depends on the projection, if used, and the version of
> database. However, in general you don't use precision, instead you
> specify the tolerance. (Aside from the 950+ known projections, you can
> also define your own coord system as well, and override tolerance for
that.)

> As of 9iR2, if using geodetics, your tolerance is specified in meters
> and is generally set at .005 meters. (Converting between defined
> projections and geodetics is accomplished using viewport
> transformations, so you can likely get the data to the arc spec you
need).

> HTH
> /Hans

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Received on Sat Feb 21 2004 - 12:12:20 CST