[GRASSLIST:4140] Re: Map import cluelessness

[C.S. Cornuelle]

Ian,

Thanks for the succinct description.  It allowed me to get as far
as i.rectify, where this ancient (according to some web searching) 
problem arose courtesy of my mailbox:

	GIS ERROR: error while writing to temp file

As per a recommendation I tried this:

	watch df -h 

and then some of this:

GRASS:/data/grassdata > date;df /data
Mon Aug  9 17:02:19 MDT 2004
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/hdb4             24590712  11836772  12753940  49% /data
GRASS:/data/grassdata > date;df /data
Mon Aug  9 17:02:34 MDT 2004
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/hdb4             24590712  11026744  13563968  45% /data

While the first call of df /data probably did not catch peak disk 
usage, the difference is around 810M, not nearly large enough to 
fill the disk or the partition.  

Any ideas on what might be going on here?  Is there a malloc set 
in i.rectify which is causing this?  FYI this map has 7500 rows and
15600 columns, so it is rather large.  10 points were identified in
i.points, and the rms value was somewhat high, nearly 100.  

Thanks for your time.

Thus spake Ian MacMillan (ian_macmillan at umail.ucsb.edu):

> So there are a couple of points to consider here.  First, I think you 
> forget to mention the program i.points (which is the one you are 
> interested in).  This program is the one that sets the points used to 
> convert the data from a non-georeferenced scanned map, into a 
> full-fledged georectified map.  To use it, you first must use i.group 
> (sets up your imagery group), then i.target (this says where you want 
> your scanned map projected to), then i.points.
> 
> This command brings up an interface in your monitor where you select 
> points to register.  There are two ways to do this.  First (using 
> keyboard), you can click a point on your scanned map, then enter the 
> coordinates of this point in the format of the projection you want.  So 
> for your case, you are going to enter in something like
> 25.78 45.80
> this is your latitude and longitude in your target location (NOT the xy 
> coordinates that are given back to you on screen).  You would typically 
> get these points from lat-long that is on your scanned map, for example 
> if you have a grid with degrees on your map.
> 
> The other method (using screen) is only valid if you have a map that 
> overlaps in space with the scanned map in your target location.  You 
> can then use this already georeferenced map to georeference your 
> scanned map.  Select "Plot Raster" at the bottom of the screen, then 
> choose the map you want from the target location.  You can then click a 
> point on your map, then click the corresponding point on the map from 
> the target location.  This will automatically force the two maps to 
> match at the points you select.
> 
> After this process is done (for a minimum of 4 points), you can check 
> how much distortion will occur in your scanned map by clicking 
> "analyze".  The larger the error, the more distorted your image will 
> be.  You can delete points in here if they seem wrong, then add new 
> ones later.
> 
> After this, run i.rectify, aftger your processor stops working, the 
> image will be in your target location.  Open up the new location (after 
> exiting from your xy location), and you are good to go.
> 
> Good luck,
> Ian
> 
> 
> On Aug 9, 2004, at 11:35 AM, C.S. Cornuelle wrote:
> 
> >I am trying to import a scanned map into GRASS 5.3 and transform it 
> >into
> >the same coordinate system/projection as a grass database, e.g. a
> >DEM in lat-lon.

<snip>

-- 
Adios,
Chris Cornuelle
bob at xmission dot com