[Qgis-user] Problem changing a shapefile's coordinates

[Alister Hood]

This was sent to me, presumably by mistake.

> -----Original Message-----
> From: kidsmake6until2019 at gmail.com
[mailto:kidsmake6until2019 at gmail.com] On
> Behalf Of Brad Nesom
> Sent: Wednesday, 28 September 2011 4:29 p.m.
> To: Alister Hood
> Subject: Re: [Qgis-user] RE: [Qgis-community-team] Problem changing a
> shapefile's coordinates
> 
> my suggestion is load each file seperately by itself. find a location
in the
> file tha tis at least close to the same point for each.note the
coordinates of
> the project.
> if all the files are in fact lat lon (4326) the values should be like
35, 98.
> or 35, -98
> if they are 100k size there is a good chance they are UTM,
> 1million probably stateplane.
> The prj file is what determines how the gis projects the shape file.
the
> coordinates don't change.
> if there is no prj file the software will probably default it to 42326
while in
> fact the values are for a completely different system.
> if you insert the unknown with a known and they line up then you know
what
> system the coords are in.
> So using the on the fly projection you can fool the system into
telling you
> what system it is in.
> 
> file a, b, c, and d
> a =4326
> b=unk
> c=utm
> 
> by adding 1 file first you will know what the prj says it is. then add
another
> to see if it lines up.
> you are trying to find the unk then you can get rid of the prj ifor
the unk
> file.
> with on the fly DISABLED 2 files with the same prj should line up (if
they
> don't they aren't the same projection) no matter what the prj says.
> use 2 known files to verify with on the fly (a,c)
> use 1 planar file with unk (zoom to extents to see scale and direction
from
> known)
> make some informed guesses and convert file d to several possibilities
> use each posssiblity by itself (this will set the crs ) then add the
unk with
> on the fly
> when you find one that lines up with unk (mystery solved) now saveas
and the
> prj will be correct
> 
> This is rather tedious but it works for identifying incorrectly
projected,
> unprojected, incorrectly identified projections.
> 
> 
> 
> On Tue, Sep 27, 2011 at 4:30 PM, Alister Hood
<alister.hood at synergine.com>
> wrote:
> 
> 
> 	Hi,
> 
> 	> -----Original Message-----
> 	> From: qgis-community-team-bounces at lists.osgeo.org
> 	[mailto:qgis-community-team-
> 	> bounces at lists.osgeo.org] On Behalf Of giannis Nj
> 	> Sent: Tuesday, 27 September 2011 10:53 p.m.
> 	> To: qgis-user at lists.osgeo.org;
qgis-community-team at lists.osgeo.org
> 	> Subject: [Qgis-community-team] Problem changing a shapefile's
> 	coordinates
> 
> 	>
> 	> Hello,
> 	>
> 	> I have a .tiff file and a .shp one, showing the same area in
the map
> 	but they
> 	> come in different coordinates. From the Properties of these
files I
> 	give them
> 	> the same projection (4326 - WGS84), same as the project
properties,
> 	but still
> 	> they don't match. Actually, the coordinates of the shapefile
remain
> 	the same
> 	> (different from the project's), something that I thought would
change
> 	by
> 	> changing the CRS.
> 
> 
> 	Like Micha said, assigning a different CRS to a layer does not
change
> 	the coordinates of features in the layer, it just tells QGIS
which CRS
> 	the coordinates are in, for the sake of 'on the fly' CRS
transformation.
> 	For a layer to show up in the correct place you must assign it
the
> 	correct CRS (if not already assigned), and either:
> 	(1) enable 'on the fly' CRS transformation, or
> 	(2) save copy of the layer, transformed into the same CRS as the
> 	project, as the other guys have described, and use that copy.
> 
> 	(1) is fine if you only need to display the layer.  If you need
to do
> 	some sort of spatial analysis using layers in different CRSs you
> 	normally need to do (2), because many tools in QGIS require
layers to be
> 	in the same CRS.
> 
> 
> 	> I guess it's not that simple to change the coordinates in a
> 	> file, so i would like to ask how it is possible to manage this
so that
> 	the two
> 	> files will come in the same coordinates. Is something in the
settings
> 	that i
> 	> forget to do? Is this able in QGIS or i have to try on another
GIS
> 	program?
> 	>
> 	> Thank you.
> 
> 
> 	Regards,
> 	Alister