TBDThis is a relatively simple case as it is represented by the element gml:Arc in GML, which does not have any ambiguities: 3 points always define a single arc. Unfortunately, this is rarely used in the AI domain.
| Note | ||
|---|---|---|
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| When moving towards a fully digital AI chain, the use of this type of arc information should be encouraged and eventually imposed as the unique way for defining arcs. |
However, this is not likely to be achieved on short term.
A border that uses arcs by 3 points looks like shown in the figure below:
A GML encoding example for this type of arcs is provided below.
| Code Block | ||||||
|---|---|---|---|---|---|---|
| ||||||
...
<gml:PolygonPatch>
<gml:exterior>
<gml:Ring gml:id="...">
...
<gml:curveMember>
<gml:Curve gml:id="...">
<gml:segments>
<gml:Arc gml:id="...">
<gml:pos>P2</gml:pos>
<gml:pos>P3</gml:pos>
<gml:pos>P4</gml:pos>
</gml:Arc>
</gml:segments>
</gml:Curve>
</gml:curveMember>
... |
In fact, this is a particular case of the more general GML concept of “ArcString”2, which is a curve segment that uses three-point circular arc interpolation in a piecewise fashion to “string” the arc segments together. The number of control points in the string is (2 x numArc)+1, where numArc is the property defining the number of the arcs in the string, such as shown in the figure below:
