Indicate vertices order orientation in polygon part and ring geometries #9523
Conversation
in polygon part and ring geometries fixes qgis#8658
and remove a fix me (refs qgis/QGIS#50447)
DelazJ
added
Editing
backport release_3.40
|
@lbartoletti May I request your review whether I summarized correctly the changes, please? Thanks. |
| .. note:: **Order of vertices in polygon parts** | ||
|
|
||
| Unlike the OGC standards, QGIS doesn't constrain vertices | ||
| of the exterior boundary of a polygon feature to be ordered counterclockwise. |
There was a problem hiding this comment.
Exact. However, you can "fix" the case using processing
There was a problem hiding this comment.
The main point I wanted to highlight in the note is the parts being oriented the same way. I thus added the "fix" tip in another paragraph.
| A hole appears in the selected geometries. | ||
| #. If no geometry is selected when the ring is drawn, | ||
| then a hole is added to each of the polygons the ring is drawn over. | ||
|
|
There was a problem hiding this comment.
Here, you can add a note indicating that after AddRing, the vertices of the inner rings are oriented in the opposite direction to the exterior ring.
There was a problem hiding this comment.
Hmmm... Isn't this covered in the note just below?
| Thus, you can find both directions in a layer. | ||
| However, every parts of the same multipolygon feature | ||
| will have their outer vertices ordered following the same direction. | ||
|
|
There was a problem hiding this comment.
| You can however use the :ref:`qgisforcerhr` algorithm to constrain features of a layer | |
| to have vertices of their outer boundaries ordered in the clockwise direction. |
| .. note:: **Order of vertices in polygon parts** | ||
|
|
||
| Unlike the OGC standards, QGIS doesn't constrain vertices | ||
| of the exterior boundary of a polygon feature to be ordered counterclockwise. |
There was a problem hiding this comment.
The main point I wanted to highlight in the note is the parts being oriented the same way. I thus added the "fix" tip in another paragraph.
| A hole appears in the selected geometries. | ||
| #. If no geometry is selected when the ring is drawn, | ||
| then a hole is added to each of the polygons the ring is drawn over. | ||
|
|
There was a problem hiding this comment.
Hmmm... Isn't this covered in the note just below?
| of the exterior boundary of a polygon feature to be ordered counterclockwise. | ||
| Thus, you can find both directions in a layer. | ||
| However, every rings of the same (multi)polygon feature | ||
| will have their vertices ordered in the opposite direction to the outer boundary's. | ||
|
|
There was a problem hiding this comment.
| You can however use the :ref:`qgisforcerhr` algorithm to constrain features of a layer | |
| to have vertices of their outer boundaries ordered in the clockwise direction, | |
| and vertices of their interior rings ordered in the counter-clockwise direction. |
fixes #8658
Also update an old fix me and describe "add ring" how-to