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 <[email protected]
<mailto:[email protected]>> 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
<[email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>>
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 <[email protected]
<mailto:[email protected]> <mailto:[email protected]
<mailto:[email protected]>>>
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
<[email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>> 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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