[GRASSLIST:5308] comparing two different maps

GRASS GRASS user
1

Hi all.

My first map was a tiff image of 2540 x 3500 pixels of 300 dpi resolution
with a scale of 1:63000. I created a xy location, imported that raster map
and digitized.

My second map covers the same geographic area, but image size is 512 x 512
pixels with 90 dpi resolution, scale unknown (it is a tif image converted
from a satellite image).

I want to digitise this map and compare the two layers. I don't know whether
it will be possible and am confused. Should lat-lang coords are must ? or
image transformation ? ...

Please help.

Thank you.
Regards,
Abhay.

2

Try to see the documentation about i.target, i.group, i.point, i.rectify....
It should work for you

Bye

Ivan

Alle 06:23, martedì 14 gennaio 2003, Abhay Kulkarni ha scritto:

Hi all.

My first map was a tiff image of 2540 x 3500 pixels of 300 dpi resolution
with a scale of 1:63000. I created a xy location, imported that raster map
and digitized.

My second map covers the same geographic area, but image size is 512 x 512
pixels with 90 dpi resolution, scale unknown (it is a tif image converted
from a satellite image).

I want to digitise this map and compare the two layers. I don't know
whether it will be possible and am confused. Should lat-lang coords are
must ? or image transformation ? ...

Please help.

Thank you.
Regards,
Abhay.

--
Ivan Marchesini
University of Perugia
Italy

3

Hi to all
I tried to use v.surf.rst!!!
I have to create a higth resolution DEM (1 m raster cells) of the landscape
along a river....
the problem is that this river has an oblique path on the screen, from NO to
SE....
So, setting the region of the study area to match the river path, I
interpolate a lot of landscape I don't need.... with obvious problem of time
to obtain the results...
because I have georeferenced aerial photos of the river I tried to use the
mask option of v.surf.rst, setting the mask to match a single photo, but I
didn't obtain good results... and the same using the MASK option of grass....

I also tried to use the procedure explained in the book Open Source
Gis.........(Neteler-Mitasova) about the generation of a dem in a surface
with faults (gully.mask, etc......).
but I didn't understand why they use an inverse mask to obtain only the DEM of
the gully.....

They have a gully area named "gully.mask" and a lot of points of the gully
topografy "gully.ascii"

They transform the ascii file in site grass data:

s.in.ascii elev.gully input=gully.ascii

after, they obtain the inverted mask:

r.mapcalc gully.mask.inv = "if(gully.mask,0,1)"

then, they use s.surf.rst:

s.surf.rst elev.gully elev=elev.gully mask=gully.mask.inv

They say that in this way is possible to interpolate only in the area of the
gully and not in the hillslope around....

The problem is:
the raster gully.mask.inv is a map that have value 0 inside the area of the
gully and 1 outside....
so, I think that, using the antecedent sintax, I obtain an opposite result
!!!!!!

Can someone help me??

Thank you and sorry for the lenght of the e-mail.....

Ivan

can someone help me???