[Qgis-user] Road Network Extraction out of Raster Images

[Kirk Schmidt]

Hallo Elvin:

This would be a bit tricky as roads are not created equal.  A paved road 
and associate paint is very different from a cobblestone or gravel 
road.  Add shadows from trees, buildings and rock cuts and the 
complexity increases.   If you used a supervised classification you 
would end up with clusters of pixel polygons or pixel points that would 
not be very consistent.  The level of work required to edit and simplify 
these  would be very time consuming.  It is for these reasons that 
original line features such as roads where digitized as simple vectors.  
As bernd suggest below, existing vector data is available for most areas 
and it is simply a matter of locating and accessing these sources.

Kirk

On 4/18/2019 12:10 PM, Bernd Vogelgesang wrote:
>
> Hi Elvin,
>
> I do not know of any trick how to extract a road network from images 
> besides a trained image classification model. But may the question be 
> allowed why you can't just use the OpenStreetMap data directly?
>
> Cheers,
> Bernd
>
> Am 18.04.19 um 15:12 schrieb Elvin Roldan:
>>
>> Hello:
>>
>> I’m writing because I’ve been a long time user QGIS and really 
>> appreciate all the work that has been put to it and all the 
>> initiatives to continue to evolve and maintain it as an important 
>> open source GIS system.
>>
>> My question is aim does anybody know how to extract a road network 
>> using spatial analysis tools within QGIS. I want to extract all roads 
>> from aerial images to convert to vectors (polylines or polygons) to 
>> do various analysis involving the existing road network.
>>
>> If anybody can point me in the right direction  I would appreciated.
>>
>> Thanks.
>>
>> Elvin Roldán
>>
>>
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-- 
Kirk Schmidt, MScF, BScF, RPF
General Manager
Nortek Resource Solutions Inc.
RR # 1
Thorburn, NS
B0K 1W0
Tel (902) 922.3607
Email: kirk at nortekresources.com
Web: www.nortekresources.com

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