[GRASS-user] A question about raster map resolutions

[Moritz Lennert]

On 21/09/16 09:35, Nikos Alexandris wrote:
> Rich Shepard wrote:
>
>>> The LiDAR source location has x- and y-resolution of 3 feet
>>> (international) and several thousand cells east-west and north-south.
>>> g.region -p for this location displays:
>>>
>>> projection: 99 (unnamed)
>>> zone:       0
>>> datum:      ** unknown (default: WGS84) **
>>> ellipsoid:  grs80
>>> north:      1286590.24500872
>>> south:      1240510.24500872
>>> west:       634966.76150938
>>> east:       664972.76150938
>>> nsres:      3
>>> ewres:      3
>>> rows:       15360
>>> cols:       10002
>>> cells:      153630720
>>>
>>>    When in the project location g.region -p produces:
>>>
>>> projection: 99 (NAD_1983_HARN_StatePlane_Oregon_North_FIPS_3601_Feet_Intl)
>>> zone:       0
>>> datum:      nad83harn
>>> ellipsoid:  grs80
>>> north:      588219.90693215
>>> south:      536993.58817534
>>> west:       7524575.13218961
>>> east:       7561596.20977101
>>> nsres:      2561.31593784
>>> ewres:      1851.05387907
>>> rows:       20
>>> cols:       20
>>> cells:      400
>>>
>>>    I want to understand why the nsres is now 2561+ feet, the ewres now
>>> 1851+
>>> feet, and the numbers of rows and columns has decreased so drastically.
>>>
>>> Looking forward to learning,
>
> Helmut Kudrnovsky:
>
>> If it is about raster reprojection, there are hints in the r.proj manual
>> about region settings before applying r.proj.
>>
>> E.g.
>>
>> A simple way to do this is to check the projected bounds of the input map in
>> the current location's projection using the -p flag. The -g flag reports the
>> same thing, but in a form which can be directly cut and pasted into a
>> g.region command.
>
> Some observation: `-g` prints out in shell style, suitable for
> `eval`uating.  The `eval` utility, for example, constructs a
> command, from the given arguments (here, the ouput of `g.region -g`)
> which is then executed by the shell.  See for example
> https://grasswiki.osgeo.org/wiki/Shell_scripting#Using_output_from_GRASS_modules_in_the_script.
>
> A ready to copy-n-paste form is obtained via `-f` (this is a recent
> addition by Moritz during the code sprint in Bonn).
>
> Maybe the `-f` flag would be a useful addition to `r.proj` as well.

AFAIR, the -g flag in r.proj already outputs flat format.

Moritz