[Qgis-developer] Re: [Qgis-user] vector editing in QGIS - questions and issues (PostGIS biased)

[Marco Hugentobler]

Hi Maciej

 The option "Enable topological editing" is for editing and maintaining common 
boundaries in polygon mosaics. If you enable it and move boundary vertices 
afterwards, it should be moved for all adjacent polygons. Similar for 
insertion of new feature, delete vertex, add vertex and even split feature.

The option "Avoid intersection of new polygons" is to quickly digitise 
adjacent polygons. If you already have one polygon, it is possible with this 
option to digitise the second one such that both intersect and qgis then cuts 
the second polygon to the common boundary. The advantage is that users don't 
have to digitize all vertices of the common boundary.

The 'search radius for vertex edits' is important if you move/add/delete 
vertex. It is the distance from the click point where qgis looks for the 
nearest matching vertex

Issue 1: The default snapping tolerance applies to the current layer if 
nothing has been saved into the project. As soon as you press 'apply' in the 
project properties, qgis takes the (more detailed) project settings which can 
be differentiated by layer. So this is a feature, not a bug :-)

Issue 2:  a) Could be a bug, I have to check that.
b) Possibly qgis makes a polygon during intersection removal where postgis 
enforces a multipolygon.

Regards,
Marco
  

Am Mittwoch 27 Februar 2008 23:00:02 schrieb Maciej Sieczka:
> Hi
>
> QUESTIONS:
>
> What do the "Enable topological editing" and "Avoid intersections of new
> polygons" in Project Properties exactly do? What is the "Search radius
> for vertex edits" in Options>Digitizing? I can't find them covered in
> QGIS manual, website and WIKI. I'd be grateful for explaining them to me
> as I have to explain them to few other folks on Saturday :).
>
>
> ISSUES:
>
> 1. Once I enter the "Project properties" and press "Apply" (without or
> with modifying any setting, with or without any layer added to project -
> doesn't matter), the "Default Snapping Tolerance", which I set in
> Option>Digitizing to "5", is not respected anymore when editing PostGIS
> layers from then on (like if set to 0). To enable sanpping I have to set
> it separately for each layer in Project Properties, which is tedious and
> was hard to guess what's going on. Looks like a bug, does it?
>
> 2. After "Avoid intersections of new polygons" is enabled, and the
> individual snapping for the layer is set in the Project Properties,
> following errors crop out:
>
> a) During digitising PostGIS multipolygons an error "Could not remove
> polygon intersection" pops up from time to time. I can't see what is the
> pattern for that. A bug?
>
> b) At saving changes to a PostGIS multipolygon layer, if a polygon
> touching another one is digitised, an "INSERT error" pops up: "ERROR:
> new row for relation "test_polygons" violates check constraint
> "enforce_geotype_the_geom"", and I cannot save changes. Seems a bug for
> sure.
>
> Here's the metadata of an example "test_polygons" layer. Issues are
> reproducible with any multipolygon though AFAICT:
>
> Storage type of this layer : Generic vector file
> Source for this layer : dbname=topsecret host=topsecret port=topsecret
> user=topsecret table="topsecret"."test_polygons" (the_geom) sql=
> Geometry type of the features in this layer : Polygon
> The number of features in this layer : 3
> Editing capabilities of this layer : Add Features, Delete Features,
> Change Attribute Values, Add Attributes, Delete Attributes, Change
> Geometries, Select Geometries by ID (unknown access method)
> Extents:
> In layer spatial reference system units : xMin,yMin 594842,5.68402e+06 :
> xMax,yMax 598419,5.68746e+06
> Layer Spatial Reference System:
> +proj=utm +zone=33 +ellps=WGS84 +datum=WGS84 +units=m +no_defs
>
> Takes place on QGIS r8182 built and running against QT 4.3.2, GEOS 3.0,
> PgSQL 8.2.6, PostGIS 1.3.2, on amd64 Ubuntu Gutsy. Same happened in
> r8171. Please fix if possible.
>
> Maciek
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-- 
Dr. Marco Hugentobler
Institute of Cartography
ETH Zurich
Technical Advisor QGIS Project Steering Committee