Segments, nodes, and junctions

Moderator: Unholy

Segments, nodes, and junctions

Postby kentsmith9 » Thu Apr 18, 2013 4:52 pm

I think we have most of the definitions for these terms under control in the Glossary, but I just noticed we are still a bit lacking on terms around nodes.

So I want to put here what I believe is the correct statements for these terms that we can discuss and debate. These are the current related Glossary entries. Words in "*" are hyperlinks to other terms or pages in the Wiki.

--------------------------------------------------

Dead-end Node: This is a *Junction* found at the end of a road segment without another segment connected to its end.

Geometry: The layout or shape of a road *segment*. Each road is made up of straight line segments. These can be arbitrarily short, effectively allowing curves. For more information see *Editing existing roads*.

Geometry node: {2 segment images and 2 landmark images here}
When editing a segment or landmark, large white circles (previously large black squares) appear where the segment changes direction changing its shape. Click and drag them individually to alter the geometry of the segment or or landmark. Click and drag the small white circles on a segment to add them to an object or press the d key while the mouse is hovered over them to delete the geometry node.

The second segment and landmark image above are "inter"-geometry nodes. These are smaller and found halfway between two geometry nodes on a segment or landmark, or a segment geometry node and the end of a segment. When you click and drag an inter-geometry node, it becomes a larger geometry node and two more inter-geometry nodes appear halfway between each side again.

For more information see *Editing existing roads*.

Junction or Junction Point:
{Junction image} The point where two or more road segments connect or the end of a dead-end segment; often 'incorrectly' referred to as a 'node'.

Junctions look different depending on the situation:

{Images appear for each entry}
* Selected and editable segment junction
* Selected and uneditable segment junction (no permissions to change)
* Changed, unsaved junction

For more information see the *Junction Style Guide*.

Node: See *Geometry Node*.

Segment: Defines a section of roadway on which vehicles may travel or a pathway where only people may travel. Multiple segments are connected by *junctions*.
-------------------------------------------------

1. What do we call the ends of a segment when the segment is highlighted? I thought they were "end nodes", but reading this sounds like only the points in the middle of a segment can be "nodes" and we call them "Geometry Nodes."

2. The answer to #1 will define if we call the end of a dead-end segment a "dead-end node" or not. Related to this question, do we really call it a "junction" when there are no other segments attached? I would say no. The current definition says a junction requires two or more segments. That would say a single segment cannot have a point that is a junction (unless it illegally wrapped upon itself). The Junction definition would also change to match this change.

3. I think the Geometry definition should change the sentence "Each road is made up of straight line segments." to "Each road is made up of one or more straight line sections." to prevent confusion with the already defined word for segment.

4. We often use the term "end node" but it is not defined. I propose we add it, but I am not sure if this is what you find at either end of a segment. I assume yes and a "dead-end node" is simply an "end node" that is not connected to another segment.

5. When we answer the above questions I can expand the definition of the term "Segment" here to include more information.
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Re: Segments, nodes, and junctions

Postby kentsmith9 » Tue May 14, 2013 3:02 pm

To clarify, we decided that there are only 4 types of nodes above and a Junction is either just a Junction or possibly a Junction Point, but it is not a Junction Node.

I will be going through the Wiki pages to update these references as required.
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Re: Segments, nodes, and junctions

Postby kentsmith9 » Mon May 06, 2013 6:19 am

Round 1 completed with the Glossary updated. Next I will go through the JSG to ensure we are in sync with this final naming decision and adjust were needed or unclear.
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Re: Segments, nodes, and junctions

Postby kentsmith9 » Mon May 06, 2013 2:45 am

harling wrote:The terms "segment" is being overloaded. It is being used to refer to both A) an object that has a junction at either end, and B) one of the straight sections between two geometry nodes.

Likewise, when "segment" is being used in sense B), the object with a junction at either end is being referred to as a "road".

Sense B) is wrong across the board.

A "segment" is a map object with two junctions--one at each end--and zero or more geometry nodes that alter its shape from a straight line connecting the two junctions.
A "road" is an identity in the map database that is associated with one or more segments.

As far as I know there is no name for the straight section between two geometry nodes (or between a junction and a geometry node)--nor does there need to be. The only time I have seen its lack of name become a problem is in this thread, when we tried to name it. ;)


The segment dilemma was solved with this proposal above. I think it answers your concern on segments. While we may not have much use for the name outside of the definition page, we still talk about that geometric element on the page discussing nodes, so I propose we use what some of us have already agreed.
jondrush wrote:
kentsmith9 wrote:3. I think the Geometry definition should change the sentence "Each road is made up of straight line segments." to "Each road is made up of one or more straight line sections." to prevent confusion with the already defined word for segment.

Sections is much better.


I will also review the wording around sense B and remove it as I agree it is wrong based on our use here.
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Re: Segments, nodes, and junctions

Postby ncc1701v » Mon May 06, 2013 1:55 am

harling wrote:A "road" is an identity in the map database that is associated with one or more segments.

A road is a series of connected (or concatenated) segments that have the same essential attributes.

(The essential attributes that are the same are defined elsewhere.)

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Re: Segments, nodes, and junctions

Postby harling » Mon May 06, 2013 1:41 am

The terms "segment" is being overloaded. It is being used to refer to both A) an object that has a junction at either end, and B) one of the straight sections between two geometry nodes.

Likewise, when "segment" is being used in sense B), the object with a junction at either end is being referred to as a "road".

Sense B) is wrong across the board.

A "segment" is a map object with two junctions--one at each end--and zero or more geometry nodes that alter its shape from a straight line connecting the two junctions.
A "road" is an identity in the map database that is associated with one or more segments.

As far as I know there is no name for the straight section between two geometry nodes (or between a junction and a geometry node)--nor does there need to be. The only time I have seen its lack of name become a problem is in this thread, when we tried to name it. ;)
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Re: Segments, nodes, and junctions

Postby kentsmith9 » Sun May 05, 2013 8:12 am

Here is what I have so far based on feedback for the visual. I think this is very close to a compromise for what everyone is proposing.

Also, we will not call a "dead-end node" a junction any more.

Nodes_and_Junctions_3.png
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Re: Segments, nodes, and junctions

Postby bgodette » Sun May 05, 2013 3:13 am

kentsmith9 wrote:
bgodette wrote:Here is where the problems begin: In the data model used by WME and presumably routing, Junctions are what we call roundabouts and Nodes are what we call intersections or junctions, and geometry "nodes" are a list of Points contained in the geometry attribute of a segment/landmark.

:lol:
In that case should we just use a convention that makes general sense and follows what we have been saying and using all along?
Which leads to Waze developers not understanding what we're talking about.
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Re: Segments, nodes, and junctions

Postby AlanOfTheBerg » Sat May 04, 2013 7:19 pm

Regardless of what the objects and properties are called in the model, we should use common generally-understood language to the user population. I am guilty of not doing this many times, but usually that's when having more technical discussions.

I call the ends of segments "end points" but can conform to whatever is preferred by the group.

I often swap between using geometry nodes and handles, but think geometry point and inter-geometry point sound better. Again, I'm not married to anything. 'cept the wife.
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Re: Segments, nodes, and junctions

Postby ncc1701v » Sat May 04, 2013 2:13 am

"By this it appears how necessary it is for any man that aspires
to true knowledge, to examine the definitions of former authors;
and either to correct them, where they are negligently set down,
or to make them himself. For the errors of definitions multiply
themselves according as the reckoning proceeds, and lead men into
absurdities, which at least they see, but cannot avoid, without
reckoning anew from the beginning."
- Hobbes, Leviathan, 1651

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