[GRASS-user] Re: documentation of georectify tool in gis.m

[Michael Barton]

Thanks much Moritz and especially for the feedback. I've had very little on
this module. This will help me improve it.

I don't know where the docs should go. A georectifier manual page seems the
most appropriate, but since it's not a standard C module, I'm not sure how
best to do this automatically.

Michael


On 1/11/07 10:13 AM, "Moritz Lennert" <mlennert at club.worldonline.be> wrote:

> Michael,
> 
> On 11/01/07 16:19, Michael Barton wrote:
>> Moritz, 
>> 
>> I'm afraid there is no FM to R. I've been so pushed to plug all the holes in
>> making GRASS usable without X11, I just haven't kept up with all the
>> documentation. I should probably relook at the mouseover help to make sure
>> it is understandable
> 
> I don't think that you should necessarily be the one to do this as well.
> You have many other things to do, and I think that documentation is the
> one thing _everyone_ can help with.
> 
> Your description below is all I needed (thanks for taking the time), and
> I think something like this would be enough for most people. Should this
> go into the gis.m manual page, a separate georectify manual page, or on
> the WIKI ? I'm willing to format it to whatever is desired.
> 
> 
>> 
>> It is pretty straightforward (IMHO).
> 
> It is once you understand it. One of my main problems was that I thought
> the "ref. map" was what you call the "base map" below, i.e. the one
> which is already georeferenced. As you can imagine I have problems
> loading that... ;-)
> 
> Another counter-intuitive (for me) feature is the fact that erasing
> works on the non-selected points. I would have expected the contrary
> (although I understand the reasoning...).
> 
> In terms of comfort, it would be great if the cursor jumped on to the
> next point after a click on the base map. Now, it automatically jumps to
> the "geographic coordinates" fields after a click on the reference map,
> but this does not happen when you click on the base map.
> 
> In addition, if you happen to click twice on the base map, the new
> coordinates get written after those that are already in the "geographic
> coordinates" field. In my eyes, if you have the cursor in the field and
> click on the map, the previous coordinates should be erased and the new
> ones written. This would make it easier if your hand slipped while
> trying to get a point on the base map.
> 
> After having done a georectification, closed the georectifier and then
> opening it again with a new group to rectify (but from the same
> origin-mapset), there are (logically) no more coordinates in the
> georectifier window, but the RMS values from the previous run are still
> visible. This could be a bit confusion. I would suggest setting them to
> empty at every new start of the georectifier.
> 
> Other than that, easy, fast and efficient !
> 
> Moritz
> 
> 
>> Here are the steps.
>> 
>> Start up in the location you want the new map to be rectified INTO (not the
>> xy location where it's from).
>> 
>> Open any georeferenced map(s), raster or vector, or some combination of
>> multiple layers in a normal map display to serve as a base map for
>> georectification.
>> 
>> Start the georectifier.
>> -Decide if you are going to georectify vectors or rasters and check the
>> appropriate radio button
>> -Create a group if you don't already have one. This uses i.group for raster
>> and its own routine for vectors (to create a group folder, etc). All maps
>> that can be georectified with the same ground control points can go into the
>> same group
>> -Select a reference xy map that you can use to set GCP's
>> -Start georectifying
>> 
>> When georectifying, you click on a GCP in the xy map and click on the
>> corresponding point on the base map. You can also enter coordinates if you
>> want. You can delete any GCP or exclude from computations. You can check the
>> RMS error for all active points. This routine bypasses i.points and
>> i.vpoints to create a points file. The points file can be used for rasters
>> or vectors, since georectifying of both is supported.
>> 
>> When you are ready to georectify the map, pick the polynomial you want to
>> use (dependent partly on the number of points you have), and press the
>> button. This will use i.rectify for rasters and v.transform for vectors.
>> AFAIK, 3rd order polynomial georectification is still broken in i.rectify.
>> But the rest should work well.
>> 
>> The georectified map(s) are projected into your active location/mapset.
>> 
>> Hope this is helpful (and maybe the start of some docs)
>> Michael
>> 
>> 
>> On 1/11/07 4:18 AM, "Moritz Lennert" <mlennert at club.worldonline.be> wrote:
>> 
>>> Hello,
>>> 
>>> I have some trouble using the georectifying tool in the GIS Manager.
>>> Before asking any questions, I would like to RTFM. Is there any
>>> documentation somewhere ?
>>> 
>>> Moritz
>> 
>> __________________________________________
>> Michael Barton, Professor of Anthropology
>> School of Human Evolution & Social Change
>> Center for Social Dynamics & Complexity
>> Arizona State University
>> 
>> phone: 480-965-6213
>> fax: 480-965-7671
>> www: http://www.public.asu.edu/~cmbarton
>> 
>> 
> 

__________________________________________
Michael Barton, Professor of Anthropology
School of Human Evolution & Social Change
Center for Social Dynamics and Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton