[Qgis-user] projection delema

[Mars Sjoden]

On Tue, May 24, 2011 at 2:53 PM, Chuck Young <wylie1066 at gmail.com> wrote:

>
>
> On Tue, May 24, 2011 at 12:26 PM, Mars Sjoden <aurorageomatics at gmail.com>wrote:
>
>> On Tue, May 24, 2011 at 12:16 PM, Chuck Young <wylie1066 at gmail.com>wrote:
>>
>>>
>>> I have a question related to the projection:
>>>
>>> I have started with a layer set to the above projection.  Its metadata
>>> shows that it is set to the NAD83 / UTM 12 projection by displaying the same
>>> details "+proj=utm +zone=12 +ellps=GRS80 +datum=NAD83 +units=m +no_defs" .
>>> I have created a new vector layer using the same projection and digitized
>>> the vector layer data over the current layer.  Then checked to be sure the
>>> new layer did in face assume the correct projection.
>>>
>>> After this I have loaded the new layer over a layer that was created
>>> earlier in the same projection, digitized over the same base layer and
>>> showing the same metadata, and they don't match up.  When I load the two
>>> together then do the zoom extents the map goes to extreme separation of the
>>> two layers.
>>>
>>> I have tried to re-project one layer but as they are on the same
>>> projection already they don't change.
>>>
>>> Why can the files become so different when they are all digitized over
>>> the same base layer at the same projection?
>>>
>>> Chuck
>>>
>>
>> Just a stab in the dark.
>>
>> What was the projection of the Map Display when these layers were edited?
>>
>> Was "On the Fly reprojection" ON while these layers were edited?
>>
>> There maybe a transformation error in datums perhaps?
>>
>> mars
>>
>
>
> Mars:  I have sent sample files to Giovanni for his review.  Possibly you
> would look at the same files.  I noticed the Extents data were different.
> Seems as the two files were on Lat Lon and the other [STR] was on some State
> Plane coordinate system even though they both had NAD83 / UTM Zone 12 as
> their projection.
>
> The Project Properties CRS was set to the default WGS84 at the time these
> files were created. (I didn't realize that.)  I had the Options CRS "Default
> CRS" set to "Global Defaulu Displayed Below will be used." And had the def
> for NAD83 / UMT Zone 12 set there as "+proj=utm +zone=12 +ellps=GRS80
> +datum=NAD83 +units=m +no_defs"  which is the def for Zone 12.
>
> I suppose that could have created some confusion.
>
> Is there any way to reset the ref from the one you will se in the Extents
> of the STR file to the one in the other two files?
>
> If so it would make things a lot easier.
>
> Thanks
>
> Chuck
>
>
Hmmm, you may be able to triangulate the Highways to the extent you know
of...



   - Try simply reseting the CRS (not reproject) of your Highways/FSR to WGS
   84.
   - Set the Map to UTM 12 For projection
   - Set On reproject on the fly transformations
   - Your Highways and FSR should display near your STR shapefile now...
   - May have to move your shapefiles to properly align if resolution
   limited information.
   - Reproject to desired projeciton



Here are the files you sent me reprojected using these steps.

mars
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