[GRASS-user] Re: grass-user Digest, Vol 31, Issue 18

Richard Chirgwin rchirgwin at ozemail.com.au
Tue Nov 11 18:41:56 EST 2008


>
> ------------------------------
>
> Message: 4
> Date: Sun, 9 Nov 2008 21:56:31 +1100
> From: "Matt B" <mattslists at gmail.com>
> Subject: [GRASS-user] Help with Georeferencing
> To: grass-user at lists.osgeo.org
> Message-ID:
> 	<4ae765870811090256g5298d380o81b9e5a3872f204a at mail.gmail.com>
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>
> Hi Group,
> I'm slowly figuring out how to use grass but encountering the odd problem.
> Actually, I haven't managed to get much done with grass at all yet but I'm
> writing that off to the learning curve.
> At the moment I'm trying to georectify a stitched together google earth
> image (I'm aware of the various legal issues that go with this and I'm just
> using a few images to see if the work I want to do is feasible with this
> type of data, if it is I'll look at purchasing data).
>
> I've imported the raster into grass using gdal, it splits it up into 3 (RGB)
> files? and I can display it (in the wrong place at the wrong scale). I also
> have the coordinates of the 4 corner points of the image and those are what
> I'm using to georeference using the georeferencing tool from the file menu.
>
> I keep getting this error when I hit the "georectify" button in the
> georeferencing tool:
>
> Traceback (most recent call last):
>   File "/usr/lib/grass/etc/wxpython/gui_modules/georect.py", line 825, in
> OnGeorect
>     self.SaveGCPs()
> TypeError: SaveGCPs() takes exactly 2 arguments (1 given)
> Traceback (most recent call last):
>   File "/usr/lib/grass/etc/wxpython/gui_modules/georect.py", line 825, in
> OnGeorect
>     self.SaveGCPs()
> TypeError: SaveGCPs() takes exactly 2 arguments (1 given)
>
> (python:11374): Gdk-CRITICAL **: gdk_window_set_geometry_hints: assertion
> `GDK_IS_WINDOW (window)' failed
>
> GRASS_INFO_MESSAGE(12418,1): Group <morondavaGE> has no target
> GRASS_INFO_END(12418,1)
>
>
> It also took me a while to figure out how to set up image groups. I'm still
> not sure if I've got that correct but that doesn't look like what the
> problem is.
> I am able to get the image aligned in qgis but stage 2 of my work will
> involve some simple image classification (no doubt the subject of the next
> few emails to this list). I'd also like to be able to know enough about how
> grass works to be able to use it properly so I'm persevering with grass for
> the time being.
>
> Thanks
> Matt
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> ------------------------------

Matt,

I realise that Hamish and others have already offered some input here,
but here's another 2c worth.

Although there's a "single click" interface for georeferencing, I still
find it works better if I follow the step-by-step process.
- i.group at the command line, to create a map group
- i.target at the command line, to point your group "towards" the place
where you want the georeferenced image to end up
- d.mon start=x0 to get an x-monitor up and running
- i.points <group> to start working.

Second thought. If you're not seeking super-high quality, use
r.composite to combine your three images into one.

Richard Chirgwin


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