[GRASS-user] Re: grass-user Digest, Vol 47, Issue 52

[Micha Silver]

On 04/01/2010 01:11 AM, Nathaniel Iwuchukwu wrote:
> Thanks Micha,
> I ran r.thin and got just one line. is there a way i can improve it?
>
Good, so we're making progress...
How many polygon areas did you create in the training map? Does it cover 
various portions of the roads?
> On Wed, Mar 31, 2010 at 1:54 PM, Micha Silver <micha at arava.co.il 
> <mailto:micha at arava.co.il>> wrote:
>
>     Nathaniel Iwuchukwu wrote:
>
>         Also, when i convert from vector to raster, i don't see
>         anything on the new raster map. its all blank. what should i
>         do. thanks
>
>     I guess that would explain why you're getting "Training map has no
>     classes".
>     Can you display the vector which covers sections of the road? Do
>     you see filled polygons?
>     If not maybe you made boundaries with no centroids? In GRASS, area
>     features must be composed of both a boundary *and* a centroid. In
>     the digitizer there's a special button for adding a centroid. You
>     need one inside each polygon boundary.
>
>
>         On Wed, Mar 31, 2010 at 11:20 AM, Nathaniel Iwuchukwu
>         <ikechinedu at gmail.com <mailto:ikechinedu at gmail.com>
>         <mailto:ikechinedu at gmail.com <mailto:ikechinedu at gmail.com>>>
>         wrote:
>
>            Thanks Micha,
>            I will definately post it once i scale through it.
>            i am getting an error when i run the i.gensigset on the
>         training data.
>            this is what i typed and the result:
>            GRASS 6.4.0RC5 (sis):~/Desktop > i.gensigset
>         trainingmap=traingis
>            group=sislabgp subgroup=sislabsub signaturefile=sislab.sig
>            Finding training classes...
>             100%
>            ERROR: Training map has no classes
>            do you have any clue why i don't have a class?
>                 Thanks Man
>            2010/3/31 Micha Silver <micha at arava.co.il
>         <mailto:micha at arava.co.il> <mailto:micha at arava.co.il
>         <mailto:micha at arava.co.il>>>
>
>
>                On 03/31/2010 01:19 AM, Nathaniel Iwuchukwu wrote:
>
>                    Thanks Micha,
>                    this looks good but am still working on it. would
>             you know
>                    the RGB for a road? from the link you
>
>                No, I can't tell what the RGB values for a road would
>         be, and
>                it will change from image to image, and from road to road.
>
>                    sent me, i will need it to capture the pixel values
>             of road
>                    polygons that i am digitizing.
>
>                You *don't* need to find the actual pixel values for
>         the road
>                polygons. You just digitize strips that cover the road, and
>                feed these areas (after converting to a raster) as the
>                training map. The gensigset module creates the
>         collection of
>                pixels values that match "roads"
>
>                    thanks Micha. you really gave me a lead.
>
>                Good. Post back to the list when you get it worked out.
>
>
>                             Nathaniel
>
>                    On Tue, Mar 30, 2010 at 4:26 PM, Micha Silver
>             <micha at arava.co.il <mailto:micha at arava.co.il>
>             <mailto:micha at arava.co.il <mailto:micha at arava.co.il>>> wrote:
>
>                        Nathaniel Iwuchukwu wrote:
>
>                            sorry my typo. i mean classification.
>
>                        I didn't intend to insult. Sometimes typos come out
>                        funny, and I can't resist pointing it out...
>
>                            but am looking for procedure on road
>             extraction from
>                            satellite imagery with high resolution
>
>                        OK, you'll probably want to use "supervised"
>                        classification. This means giving the
>             classification
>                        algorithm a "training" layer. So the process
>             involves
>                        1-  First create a vector layer using the grass
>             digitizer
>                        with small polygons covering some sections of
>             the roads
>                        in the satellite image. Convert the vector to a
>             raster
>                        (v.to.rast). This will be the training map.
>                        2- Now group the satellite bands into an
>             imagery group
>                        (i.group)
>                        3- Run i.gensigset with the training raster and the
>                        imagery group.
>                        4- Now use i.smap with the signature file and
>             imagery
>                        group as input, and a classification map as output.
>                        5- If the results look good, run r.thin on this
>             raster,
>                        and then r.to.vect to see what you get.
>
>                        Here's a more detailed explanation that you
>             might find
>                        helpful:
>             http://www.surfaces.co.il/?p=3
>
>                        Regards,
>                        Micha
>
>
>
>                --         Micha Silver
>         http://www.surfaces.co.il/
>                Arava Development Co. +972-52-3665918
>
>
>
>
>         This mail was received via Mail-SeCure System.
>
>
>
>     -- 
>     Micha Silver
>
>     Arava Development Co. +972-52-3665918
>     http://www.surfaces.co.il <http://www.surfaces.co.il/>
>
>
>
>
> This mail was received via Mail-SeCure System.


-- 
Micha Silver
http://www.surfaces.co.il/
Arava Development Co.  +972-52-3665918

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