Dear List:
This is my second time asking the list for another probable newbie problem.
To give everyone a background, we are doing a project that aims to popularize the use of open source system and GRASS GIS for coastal resource management among local government units in southern Philippines. We are still on a pilot stage and we are interested in mapping coastal habitats from scanned aerial photos. We are having a hard time knowing the right method.
Based from archive search, tutorials and help documents, we manage to import Tiff file and rectifying the image using 4-6 control points. However, when we open the raster file in the targeted location, all we see is a clump of several (30-40) big pixels of varying grey shades. We were expecting that the end image will just be the same grey scaled picture tilted according to the reference North. From there, we could have digitized coastal features as polygons representing various habitats. We hope to reach the stage of printing maps for CRM plans.
Has anyone did a similar work or knows how we can do it? Please share us some step by step procedure and if possible additional electronic references as we have very limited literature.
Thank you so much,
November A. Romena
GIS Practitioner
Bureau of Fisheries & Aquatic Resources
Philippines
I am not sure, but it sounds to me like you might not have your region
resolution set correctly (much too coarse). Almost every grass function
requires your region to be set. Make sure that it is in units that make sense,
so in degrees for a lat-long, or meters for a utm location.
g.region res=1 for a utm with full resolution photo
or
g.region res=00:00:00.03333 for a lat-long
Also, if there is any significant topography, you will need to use a digital
elevation model to orthorectify your image. Topography + lens effects =
distorted projection. Use i.ortho.photo.
Good luck,
Ian
Quoting nromena@skyinet.net:
Dear List:
This is my second time asking the list for another probable newbie problem.
To give everyone a background, we are doing a project that aims to
popularize the use of open source system and GRASS GIS for coastal resource
management among local government units in southern Philippines. We are
still on a pilot stage and we are interested in mapping coastal habitats
from scanned aerial photos. We are having a hard time knowing the right
method.
Based from archive search, tutorials and help documents, we manage to
import Tiff file and rectifying the image using 4-6 control points.
However, when we open the raster file in the targeted location, all we see
is a clump of several (30-40) big pixels of varying grey shades. We were
expecting that the end image will just be the same grey scaled picture
tilted according to the reference North. From there, we could have
digitized coastal features as polygons representing various habitats. We
hope to reach the stage of printing maps for CRM plans.
Has anyone did a similar work or knows how we can do it? Please share us
some step by step procedure and if possible additional electronic
references as we have very limited literature.
Thank you so much,
November A. Romena
GIS Practitioner
Bureau of Fisheries & Aquatic Resources
Philippines
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Ian MacMillan
Geological Sciences-UCSB
"insert witticism here"