[GRASSLIST:2735] Re: i.rectify and image resolution

[ulf at mail.zmt.uni-bremen.de]

I copied the new datum/ellipse files over the original ones in my
grass5/etc directory. I then deleted and re-created the target
location/mapset with the resolution values, ellipsoid and map datum
you suggested. Anyway, I am still not able to specify a higher
resolution than 0.01 in i.rectify if I choose the option "2. Determine
the smallest region which covers the image". The other option ("1. Use
the current region in the target location") works apparently well.

Many thanks for your advice + help!
Regards, Ulf

 > As promised, here are the datum.table and ellipse.table I used for SAD-69.
 > This and sam69 are similar except the datum of SAD-69 is more precise for
 > northern Brazil.
 > 
 > In the original files I was getting an error when trying to use the Brazil
 > system.
 > 
 > Charles Beaudry
 > 
 >  > I have had problems with the SAM69 datum.  There appears to be a confusion
 >  > in the ellipsoid and datum files.  I fixed it but don't have it with me.  I
 >  > will get it to Markus tonight for uploading to CVS and send a copy directly
 >  > to you.
 >  > 
 >  > I would set up the right projection and set the resolution of my destination
 >  > location to 0:00:0.972 or 0.00027 in decimal before trying to run i.rectify.
 >  > 
 >  > Charles Beaudry
 >  > 
 >  >  > Hello Grass experts,
 >  >  > 
 >  >  > I hope you can help me with the following. I'm using grass 5.0.0pre2
 >  >  > on ix86 Linux 2.4. I have an x,y-location with a satellite (I think
 >  >  > Landsat-) image I received from a colleague. The region is:
 >  >  > 
 >  >  >  CURRENT REGION: N=1600  S=0  RES=1  ROWS=1600
 >  >  > 		    E=1600  W=0  RES=1  COLS=1600
 >  >  >  PROJECTION: 0 (x,y)
 >  >  >  ZONE:       0
 >  >  > 
 >  >  > Now, I want to rectify the image. I created a target location in
 >  >  > lat/long-coordinate system with the highest resolution I could set,
 >  >  > and the "sam69" spheroid (my image is from equatorial Brazil -- is
 >  >  > this the right choice?). 
 >  >  > 
 >  >  >  CURRENT REGION: N= 0:43:48S  S=1:12:36S  RES=0:00:00.000036  ROWS=48000000
 >  >  > 		    E=46:55:48E  W=  46:27E  RES=0:00:00.000036  COLS=48000000
 >  >  >  PROJECTION: 3 (Latitude-Longitude)
 >  >  >  ZONE:       0
 >  >  >  DATUM:      ** unknown (default WGS84) **
 >  >  >  ELLIPSOID:  sam69
 >  >  > 
 >  >  > Then I made an image group, set the target location, and marked points
 >  >  > via i.points (I have tried a set of 8-12 GPS positions of points
 >  >  > +-well recognizable in the image).
 >  >  > 
 >  >  > Afterwards, I called i.rectify. I specified "choose smallest region
 >  >  > that covers the image" but I was not able to set a higher resolution
 >  >  > than 0.01. The resulting image in the targe location has consequently
 >  >  > only e very rough raster: 
 >  >  > 
 >  >  >  CURRENT REGION: N= 0:43:48S  S=1:12:36S  RES=0:00:36  ROWS=48
 >  >  > 		    E=46:55:48E  W=  46:27E  RES=0:00:36  COLS=48
 >  >  >  PROJECTION: 3 (Latitude-Longitude)
 >  >  >  ZONE:       0
 >  >  >  DATUM:      ** unknown (default WGS84) **
 >  >  >  ELLIPSOID:  sam69
 >  >  > 
 >  >  > I have no idea how to increase the resolution -- can you help me?
 >  >  > 
 >  >  > Many thanks, Ulf


-- 
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 Ulf Mehlig    <ulf.mehlig at zmt.uni-bremen.de>
               Center for Tropical Marine Ecology/ZMT, Bremen, Germany
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