Documentation about true curves (aka CAD data) being stored separately from ST_GEOMETRY info (within SHAPE object/column)

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07-09-2022 05:53 AM
Status: Open
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Bud
by
Notable Contributor

Regarding SDE.ST_GEOMETRY shape object columns (Oracle):

Rumor has it, true curve info (aka CAD blob data) is stored separately from ST_GEOMETRY info — all within the same shape object/column. In other words, if we query the geometry via ST_GEOMETRY functions, we don't have access to true curve data, since it's stored in a separate object attribute (an LOB attribute).

(I imagine the wording above is wrong, but that's because I don't have any documentation to reference.)

Could information about the above be added to the docs? Otherwise, I'm just fumbling around in the dark.

I know the usual suspects are likely to say, "You can't access the CAD blob via ST_GEOMETRY anyway, so it's a moot point." That might be, but I still need to understand how it's been set up...so I can understand what the limitations are and how to work around them. For example, I need to understand how ST_GEOMETRY pre-densifies the true curves into straight segments. What logic is used for the pre-densification?

 

Edit - Related: Why did a polygon lose 76 sqft (Shape.Area) when exporting from Oracle ST_Geometery to File GDB?

3 Comments
Bud
by

(merged from a separate idea)

It would be helpful if documentation could be added about about curves and CAD BLOBs in ST_Geometry.

For example, expand on details like this:

From @ShannonShields

Features with curve geometry/circular arcs have two representations in enterprise geodatabases. The ST_Geometry shape stores a densified arc version of the geometry, and the true curve is stored in a blob format read by ArcGIS, but not by the DBMS.

https://community.esri.com/t5/geodatabase-questions/why-did-a-polygon-lose-76-sqft-shape-area-when/m...

Some related GIS Stack Exchange posts: 
https://gis.stackexchange.com/search?q=%5Bst-geometry%5D+cad

SSWoodward

@Bud I have merged your two posts so that both of your comments are preserved in the same space. 

Thanks as always for your ideas!