[GRASSLIST:4056] Re: coastal photos to habitat map

[Ian Macmillan]

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 at 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
>
>


-----------------------------------------------------
Ian MacMillan
Geological Sciences-UCSB

"insert witticism here"