[GRASSLIST:2135] Re: New Location

[Glynn Clements]

Maliheh wrote:

> At first I should say thank you for your responses. Now I have a
> better idea about my work.
> 
> Till now I know that we have to import our scanned map in a xy
> location, then by use of i.group, i.target and i.points, transform it
> to a second location (lat/long in my case).
> 
> But I don't understand how we should specify our map scale. I read the
> manual about grid resolution:
> 
>  
> 
>           Resolution: 100*100 dots per inch
> 
> 100 dpi = 100 rows / 2.54 cm = 39.37 rows/cm
> 
> scale of the map: 1:12000
> 
> Distance in nature / scanned rows per cm = 12,000 cm / 39.37 rows 
> 
> = 304.8 cm/row = 3.048 m/row   GRID RESOLUTION
> 
>  
> 
> but when I enter this value GRASS shows me:
> 
>   projection:   0 (x,y)
>   zone:         0
>   north:       36
>   south:       35
>   east:        52
>   west:        51                                                                       
>   e-w res:     1  (Changed to conform to grid)
>   n-s res:     1  (Changed to conform to grid)
>   total rows:                1
>   total cols:                1
>   total cells:               1
>  
> 
> Now would you please tell me my wrong, again ? 

The boundary (North/South/East/West) coordinates need to have the same
units as the resolution. E.g. if you are specifying the resolution in
metres, then the boundary coordinates must also be in metres (and not
in e.g. degrees).

For an X/Y location, it doesn't matter exactly which units you use, so
long as they are consistent. But you appear to be specifying a
resolution of approximately 3 units for a map which is one unit high
(36 - 35) by one unit wide (52 - 51).

BTW, for a Lat/Lon location, you need to use degrees, while projected
(e.g. UTM) locations typically need to use either metres or feet.

-- 
Glynn Clements <glynn.clements at virgin.net>