[GRASS-user] Re-projected Data Position Mismatch

[Jeshua Lacock]

Greetings,

I am attempting to merge data in a couple different projections into a single projection. But as you can see in the following image, the vector data does not align with the raster tiles. The horizontal positions match, but they don’t match vertically.

http://3DTOPO.com/misalignedData.jpg

I’ve never ran into this issue before using GRASS after merging countless projections together.

All of the data shown in the image is in “epsg: 3857” projection, here is the contents of its PROJ_INFO file:

name: WGS 84 / Pseudo-Mercator
datum: wgs84
ellps: wgs84
proj: merc
lat_ts: 0.0
lon_0: 0.0
x_0: 0.0
y_0: 0
k: 1.0
wktext: defined
no_defs: defined
towgs84: 0.000,0.000,0.000

I will refer to this location as the Comp Location.

If I import a raster tile as a new location, it has this as a resulting PROJ_INFO file:

name: WGS 84 / Pseudo-Mercator
datum: wgs84
ellps: wgs84
proj: merc
lat_ts: 0.0
lon_0: 0.0
x_0: 0.0
y_0: 0
k: 1.0
nadgrids: @null 
wktext: defined
no_defs: defined


The only difference that I can tell is that the raster tile location has a "nadgrids: @null” line which I had to delete to import the raster tiles into the first location with r.proj, the Comp Location has a towgs84 transformation (but is 0,0,0), and no PROJ_EPSG file exists in the Comp Location. Alternatively I can import the raster tiles directly into the Comp Location using r.in.gdal since the projections match (I don’t get any mismatched projection warnings). In both cases, the raster tiles are located in the same position. 


The PROJ_INFO file from the locations that the vector orange grid and green bounds was imported from is as follows:

name: GCS_North_American_1983
datum: nad83
ellps: grs80
proj: ll
no_defs: defined


I had imported the orange grid and green bounds from two different locations so I could try to determine what data was in the wrong position (raster tiles or vector) but, but the both the vector layers imported are in the same lonlat projection, so I guess is wasn’t a really good test, thus I am not entirely sure which data is in the correct location.

Any suggestions would be greatly appreciated.


Thanks,

Jeshua Lacock
Founder/Engineer
<3DTOPO.com>
GlassPrinted.com