Re: [GRASS-user] Road and river extraction using GRASS

2012-10-18 Thread Moritz Lennert 

On 17/10/12 19:50, António Rocha wrote:

Greetings,
Is there any GRASS module that can be used to river and road extraction
from satellite images? Some feature extraction algorithm


See here for an example of a python script implementing a Sobel edge 
detection filter:

http://www.webrian.ch/2012/04/line-extraction-with-grass-gis.html

Moritz
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Re: [GRASS-user] Road and river extraction using GRASS

2012-10-17 Thread Anna Kratochvílová 
Hi,

On Wed, Oct 17, 2012 at 7:50 PM, António Rocha
 wrote:
> Greetings,
> Is there any GRASS module that can be used to river and road extraction from
> satellite images? Some feature extraction algorithm

you can try new (and experimental) modules from grass7 addons - i.edge
and r.houghtransform. i.edge is for detecting edges using canny edge
detection algorithm [1] and r.houghtransform uses hough transformation
[2] to detect straight lines (maybe good for roads but not usable for
rivers).
r.houghtransform can take the output of i.edge as an input.
Unfortunately there is no information in the man page yet but you can
always ask.

Anna

[1] http://en.wikipedia.org/wiki/Canny_edge_detector
[2] http://en.wikipedia.org/wiki/Hough_transform


> Thank you
> Regards,
> Antonio Rocha
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[GRASS-user] Road and river extraction using GRASS

2012-10-17 Thread António Rocha 

Greetings,
Is there any GRASS module that can be used to river and road extraction 
from satellite images? Some feature extraction algorithm

Thank you
Regards,
Antonio Rocha
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