[GRASS-user] Something wrong: Reprojection of raster maps in various platforms: projected coordinates are different

[Moritz Lennert]

On 20/10/15 19:08, Uttam Kumar wrote:
>
>
> I have been trying for a long time. Something wrong is going on. I
> appreciate if you can correct me.
>
>
> I have all my source images in sinusoidal projection in a location
> called "Landsat_sinu".
>
> My target locatoin is "Landsat_laea" I tried using the default option in
> GRASS GUI as follows:
>
> 1.) *Select coordinate system parameters from a list*
>
> 2.) Projection code: *laea*
>
> 3.) Datum with associated ellipsoid:
> Central parallel: *30*
> Central Meridian: *-96*
> False easting: *0*
> False northing: *0*
>
> 4.) Datum code: *nad83*
> 5.) Select from the list of datum transformation: *1 used in whole nad83
> region*
>
> +proj=laea
> +lat_0=30
> +lon_0=-96
> +x_0=0
> +y_0=0
> +no_defs
> +a=6378137
> +rf=298.257222101
> +towgs84=0.000,0.000,0.000
> to_meter=1
> +datum=nad83
>
> Finish.
>
> Is everything ok with this for the below (required) target definition?
>
> **PROJ.4 : '+proj=laea +lat_0=30 +lon_0=-96 +x_0=0 +y_0=0 +datum=NAD83
> +units=m +no_defs '**
>
> Looks like at some point I am making a small mistake. I must get this as
> the projected coordinates.
>
> *north=1064601.38274499
> south=830176.771464028
> east=-1960125.15283348
> west=-2265106.68066176*

And what is wrong with these coordinates ? Those are exactly the ones I 
get and they are very close to the ones you got from ENVI:

 >     > Upper Left  (-2265106.681W, 1064601.383N)
 >     > Lower Left  (-2265106.681W,  830181.383N)
 >     > Upper Right (-1960126.681W, 1064601.383N)
 >     > Lower Right (-1960126.681W,  830181.383N)

i.e. 4.6m difference for South and 1.5m difference for East. You would 
have to check how the NAD83 conversion is done exactly to see if the 
difference could come from there.

Moritz


>
>
> Any help is appreciated.
>
> Uttam.
>
>
> On Wed, Oct 14, 2015 at 4:52 PM, Moritz Lennert
> <mlennert at club.worldonline.be <mailto:mlennert at club.worldonline.be>> wrote:
>
>     [Please keep conversations on the list]
>
>     On 14/10/15 23:19, Uttam Kumar wrote:
>
>         _
>
>         _
>         _*This information is for the original data (Source):*_
>
>         *PROJ.4 : '+proj=sinu +lon_0=0 +x_0=0 +y_0=0 +a=6371007.181
>         +b=6371007.181 +units=m +no_defs '*
>
>
>         Coordinate System is:
>         PROJCS["Sinusoidal",
>               GEOGCS["GCS_Unknown",
>                   DATUM["Unknown",
>                       SPHEROID["S_Unknown",6371007.181,0.0]],
>                   PRIMEM["Greenwich",0.0],
>                   UNIT["Degree",0.0174532925199433]],
>               PROJECTION["Sinusoidal"],
>               PARAMETER["False_Easting",0.0],
>               PARAMETER["False_Northing",0.0],
>               PARAMETER["longitude_of_center",0.0],
>               UNIT["Meter",1]]
>         Origin = (-10801805.197699999436736,4130102.079069999977946)
>         Pixel Size = (30.000000000000000,-30.000000000000000)
>
>         *
>         _This information is for the destination data (Target):_*
>
>         *PROJ.4 : '+proj=laea +lat_0=30 +lon_0=-96 +x_0=0 +y_0=0
>         +datum=NAD83
>         +units=m +no_defs '*
>
>
>     In your first mail you said:
>
>     Lambert Azimuthal Equal Area, Datum: WGS84
>
>     but here the datum is NAD83.
>
>     Using your projection info, I get almost exactly the same results in
>     GRASS as you report from ENVI:
>
>     On 08/10/15 21:36, Uttam Kumar wrote:> Reprojected in ENVI (Lambert
>     Azimuthal Equal Area, Datum: WGS84)
>     > -------------------------------------------------------------------------
>     > Corner Coordinates:
>     >
>     > Upper Left  (-2265106.681W, 1064601.383N)
>     > Lower Left  (-2265106.681W,  830181.383N)
>     > Upper Right (-1960126.681W, 1064601.383N)
>     > Lower Right (-1960126.681W,  830181.383N)
>
>
>     GRASS 7.0.1 (test_LAEA):~ > v.info <http://v.info> -g Image_Boundary_box
>     north=1064601.38274499
>     south=830176.771464028
>     east=-1960125.15283348
>     west=-2265106.68066176
>
>
>     Don't have the time now to explore the exact differences, but either
>     it's a question of definition of the bounding box, or it possibly be
>     a question of which specific NAD83 transformation parameters were used.
>
>     Moritz
>
>
>