[Qgis-user] topology checker - Check if point features are covered by line features

[Nicolas Cadieux]

Hi,

Small correction,

If you extract the end nodes (vertices) of the line, you can use the 
following rule.  End node layer must be covered by endpoints of line 
layer or node layer must be covered by line.  I therefore assume the 
QGIS topology checker can work for endnode only and not for "middle 
node" of the line.  This is should be reported as a bug I think.

Nicolas

On 2020-04-17 12:42 p.m., Nicolas Cadieux wrote:
> Hi Marshal,
>
> I looked at your data. The first problem is that none or your line 
> nodes intersect with a point.  It looks close... but it's not close 
> enough.  By using "snap geometry location", I was able to create a new 
> line that snaps to your point.  (called Topologie snapped_line in the 
> file I will send you in private).  A "Select by location" or a "Join 
> Attributes by location" confirms that the points now intersect the 
> Topologie snapped line layer. The Join Attributes by location will 
> permit you to find the problems as you can discard records that do not 
> intersect.  This will give you what you want.
>
> As for the topology Checker, it seems that a line cannot cover a point 
> or a point cannot cover a line even if point and line nodes intersect 
> (Can someone confirm this?).  I can only assume that QGIS works with 
> the correct assumption that a point and a line does not have a surface 
> to cover and therefore, cannot cover anything.  I assume, based on 
> your observations that ESRI does not follow that assumption.
>
> You can however create a 1 m buffer around your line (Topologie 
> Buffered_line in the file).  Then, you can create the rule (polygon 
> must contain point). That rule will work in the topology Checker.
>
> Cheers!
>
> Nicolas
>
>
> On 2020-04-13 10:25 a.m., Nicolas Cadieux wrote:
>> Hi,
>>
>> I don’t have QGIS in front of me.  I looked around on the the net and 
>> was surprised to see the «covered By » option for points and lines.  
>> Unless a line is snapped, or intersects a point exactly on a Line 
>> node, it’s just about impossible to calculate if a line « covers » a 
>> point.  This is something easy to do with a polygon but not a line 
>> because of float point precision error.  You could buffer the lines 
>> and see if that helps. You could create a 1m buffer on the line (or 
>> the point).  Make sure both layers are in the same crs so that 
>> additional calculations don’t need to be done.
>>
>> You could at the « select by location » side.  I would look at « snap 
>> with » or «intersects with »options.
>>
>> Nicolas Cadieux
>> Ça va bien aller!
>>
>>> Le 13 avr. 2020 à 06:11, Marshal Mappers <marshalmappers at gmail.com> 
>>> a écrit :
>>>
>>> 
>>> Hello everyone,
>>> I want to use the topology checker to check if point features are 
>>> covered by line features. For example are the bus stops covered by 
>>> the bus lines.
>>> Therefore I use the topology checker with the following rule: 
>>> "points" must be covered by "lines". But I get the error for all 
>>> points that "point is not covered by segment".
>>> I even get the error for points that I edited on the line with 
>>> snapping.
>>> Here my questions:
>>> 1. Is it possible to check if point features are covered by line 
>>> features? With topology checker? In general?
>>> 2. What does the rule: "points" must be covered by "lines"check? 
>>> Under what cicumstances is a point feature covered by a line feature?
>>>
>>> I tried this in QGIS Versions 2.18.26; 3.4.15; 3.10.2
>>> My OS ist Windows 10
>>> I tried with shapefiles and geopackage layers
>>> The CBS of point and line layers are the same. Here I tried the 
>>> coordinate systems with epgs: 31468 (DHDN / 3---degree Gauss-Kruger 
>>> zone 4) and 25832 (ETRS89 / UTM zone 32N).
>>> If anyone could explain or point me to the right direction, that 
>>> would be awesome.
>>>
>>> Thank you!
>>>
>>> Best regards
>>>
>>> Marshal
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