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

[Elvin Roldan]

Hell again:

Thanks for the help I followed youre recommendations and use base layer for openstreet map and edited for my needs. None the less I will keep trying to develop this in spatial analysis due that Im working with drone collected data and a lot of areas (whole municipalities) to develop infrastructure maps. 

I will keep posted on progress. Thanks for the help.

Elvin Roldán

> On Apr 18, 2019, at 12:04 PM, Kirk Schmidt <kirk at nortekresources.com> wrote:
> 
> 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
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