# Concepts

## What's ArcSDE

### Storing Geopraphic Features in a SQL database

### Data Access

<uml>
object "Database\nConnection" as dbconn
object "Spatial\nReference" as spr

dbconn -* query
query - cursor
cursor -* value

spr o-* Shape
value <|--- Shape

value <|-- "Type 1"
value <|-- "Type 2"

Shape <|-- point
Shape <|-- linear
Shape <|-- area 

</uml>

# Geometry

## Introducing Geometry

### Shape validation

#### ArcSDE shape verification rules

The points of an area shape are stored counterclockwise although the ArcSDE software can return points in either direction. If you generate an area shape whose coordiantes are clockwise, the ArcSDE software changed the rotation to ensure that the coordinate list follows a counterclockwise direction.

## Operations of Geometry Objects

### Spatial relations

#### Predicates

The pattern matrix contains the acceptable values for each of the intersection matrix cells. The possible pattern values are
  * T : An intersection must exist; dim = 0, 1, or 2.
  * F : An intersection must not exist; dim = -1
  * * : It does not matter if an intersection exists or not; dim = -1, 0, 1, or 2.
  * 0 : An intersection must exist and its maximum dimension must be 0; dim = 0.
  * 1 : An intersection must exist and its maximum dimension must be 0; dim = 1.
  * 2 : An intersection must exist and its maximum dimension must be 0; dim = 2.

#### Equal

|      |            ^  b                                |||
|      |            ^  Interia  ^  Boundary  ^  Exterior  ^
^  a   ^  Interia   |  T        |  *         |  F         |
| :::  ^  Boundary  |  *        |  *         |  F         |
| :::  ^  Exterior  |  F        |  F         |  *         |

### Representations of Geometry

#### Well-known representations of geometry

^  Geometry Representation  ^  Specification maintained by:  ^  Encoding  ^  Supports 2D  ^  Supports Elevations                                                               ^
| Well-Known Text(WKT)      | ISO/OGC                        | ASCII      | Yes           | Yes((Additional tags have been added by ESRI to support Elevations and Measures))  |
| Well-Known Binary(WKB)         | ISO/OGC                        | Binary     | Yes           | No                                                                                 |
| Shape File                | ESRI                           | Binary     | Yes           | Yes                                                                                |
| ArcSDE Binary             | ESRI                           | Binary     | Yes           | Yes                                                                                |


#### The well-known text representation for geometry