On 04/01/2010 02:52 PM, Nathaniel Iwuchukwu wrote:
i created 11 polygons from different portions of the road.
So if I understand correctly, the procedure is working, but you're not
getting the results you'd expect?
Maybe you could supply to the grass-users list some URL's of images of
what the satellite rasters look like, with your training polygons, and
the resulting roads. Then perhaps someone will be able to suggest how to
get more complete results.
2010/4/1 Micha Silver <mi...@arava.co.il <mailto:mi...@arava.co.il>>
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 <mi...@arava.co.il
<mailto:mi...@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
<ikechin...@gmail.com <mailto:ikechin...@gmail.com>
<mailto:ikechin...@gmail.com
<mailto:ikechin...@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 <mi...@arava.co.il
<mailto:mi...@arava.co.il> <mailto:mi...@arava.co.il
<mailto:mi...@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
<mi...@arava.co.il <mailto:mi...@arava.co.il>
<mailto:mi...@arava.co.il
<mailto:mi...@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
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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