[RNFdev] Some thoughts of FSA Centroids and Polygons

[Sampson, David]

I think we're both on the same wave-length.

Maybe my idea will become more clear (or become irrelavant) when we get
to the point of creating the FSA polygons.... Like I said it was a
brainstorm.  And maybe at such it is still an immature thought.


 

-----Original Message-----
From: Dan Putler [mailto:putler at sauder.ubc.ca] 
Sent: September 28, 2006 12:15
To: can_rnf at geodata.osgeo.org
Subject: Re: [RNFdev] Some thoughts of FSA Centroids and Polygons

Hi Dave,

Sorry for being a bit thick, but I am still not sure I understand exact
problem you are trying to tackle. I think the process you are proposing
makes sense in terms of creating polygons that have "good hygiene".
Although, there are a couple of comments/questions. First, the thinned
RNF typically won't produce closed polygons based on the road segments
alone, and we will need to digitalize some of the non- road line
segments. Any overshooting and undershooting problems will largely be
associated with the added line segments as opposed to the original RNF
road segments (working with this data, it looks like StatsCan did a
thorough job of cleaning the geometry of the road segments, so they tend
not to overshoot or undershoot, assuming they exist at all in the RNF).
However, your basic point that the polygons will need some post creation
cleaning is spot on. Although, as indicated above, in the vast majority
of cases the problems will be with the added segments, so it will likely
be more of an issue of fixing less than perfect added segments, more
than investigating the causes of the error.

In terms of the attribute data, my guess is that we will need to create
FSA polygons on a one by one bases. As a result, I think it makes more
sense to add an attribute table with the FSA field to the polygon at the
time of its creation. I don't think it would be too hard to modify
Frank's  python script to do this.

Let me know if I'm still not understanding the issue.

Dan

On 28-Sep-06, at 6:15 AM, Sampson, David wrote:

> I guess my brain storm made sense to only my brain.
>
> I'll try to clarify. Some abstract thought was probably involved in my

> brain.
>
> The polygons I originally referred to were polygons created by the 
> thinned out RNF.... When a network of roads create a filled in shape 
> this can be thought of as a polygon. So changing the road network to a

> series of polygons. This is obviously an imperfect method for all 
> areas, but may work well for the urban areas.
>
> Then the FSA centroids will occur SOMEWHERE within these polygons...
>
> These FSA centroids can act as vector polygon labels. These labels 
> hold the attribute data about a particular polygon.
>
> 1. Change vector lines to polygons
> 2. clean danglers and overshoots (loose ends that extend PAST an 
> intersection 3. investigate undershoots (where two lines have not meta

> and require a virtual extension or more data 4. Attribute tabular data

> through the FSA centroid as labels 5. investigate tagged polygons as 
> bellow
>
> Does this make more sense?
>
> What is your unfeasible idea?
>
>
> -----Original Message-----
> From: Dan Putler [mailto:putler at sauder.ubc.ca]
> Sent: September 27, 2006 16:43
> To: can_rnf at geodata.osgeo.org
> Subject: Re: [RNFdev] Some thoughts of FSA Centroids and Polygons
>
> Hi Dave,
>
> I'm unclear on a couple of things. You indicate:
>> The thought is
>>
>> 1. Create the reduced RNF
>> 2. Create the FSA Centorids
>> 3. in a GIS import both the reduced RNF and the FSA centroids 4. do 
>> some queries:
>>         a. find all polygons with one FSA point
>>         b. find all polygons with more than one FSA point
>>         c. find all polygons lacking any FSA tag 5. use this info to 
>> help with manual edits.
> What I'm confused about two things. First, which polygons are you 
> referring to above? The reduced RNF contains only road segments and 
> other lines (not polygons), FSA centroids contains only points, or are

> you referring to the CSD polygons? The mention of FSA centroids leads 
> to my second question, specifically, are the FSA centroids the ones 
> available from geoconnections? If yes, they appear to have some 
> accuracy issues.
>
> I've also been thinking about other things we could that would be 
> easier than creating FSA polygons. I have an idea, but I don't know if

> it feasible.
>
> Dan
>
>> From that we can hypothesise that in
>>         case A the polygon is either correct (requiring some manual
>> cleaning) or requires enlargement (manual merges maybe)
>>
>>         case B the polygon requires additional information such as 
>> other non-road features
>>         case C the polygon has been split too much and something 
>> needs to be blown away.
>>
>> Some of this might be able to be automated or atleast again a 
>> probability choices made.
>>
>> Any thoughts
>>
>