[Qgis-user] Problem reprojecting a SHP

[Matt Boyd]

who mamages the epsg codes and transformations. I've never paid it
much attention but I thought it had something to do with the proj4
packages.

On Fri, Jun 24, 2011 at 12:50 AM, Gerardo Jimenez <gejst5 at hotmail.com> wrote:
> Thanks for your answer but I found the problem and its solution. First my
> data is in Nad 27, I am positivi about that. I found that QGis, depending on
> the version, uses different epgs settings for UTM nad 27. Qgis 1.7 use an
> argument to specify transformation parameters for WGS (+towgs84=). This is
> the EPSG codein QGis 1.7
>
> +proj=utm +zone=14 +ellps=clrk66 +towgs84=-10,158,187,0,0,0,0 +units=m
> +no_defs
>
> Qgis 1.4,1.5 and 1.6 all stand alone versions on Windows  do not define
> these parameters. And that is the main reason of the problem.  I found an
> interesting link at
>
> http://earth-info.nga.mil/GandG/coordsys/onlinedatum/CountryNorthAmericaTable.html
>
> that helped me to clarify that we can build a custom crs and add the
> specific parameters for the area you are working. The ones of Qgis 1.7 are
> the “Canadian Mean Solution” on this table. The parameters for my data on
> utm zone 14N in Mexico are
>
> +proj=utm +zone=14 +ellps=clrk66 +towgs84=-12,130,190,0,0,0,0 +units=m
> +no_defs
>
> With these parameters there are no differences in transformations made in
> QGis, ArcMap and another program I use called Didger.
>
> For those interested in transformations dealing with local datums this link
> is a good reference
>
> http://www.ecdisregs.com/get_pdf.php?id=62&action=view
>
> Thanks for your support!
>
> Gerardo Jiménez Delgado
> Instituto de Investigaciones Antropológicas
> Universidad Nacional Autónoma de México
> Ciudad Universitaria s/n
> Coyoacan 04510 Mexico City
> Mexico 56 22 95 16
>
>> Date: Thu, 23 Jun 2011 21:59:40 +1000
>> Subject: Re: [Qgis-user] Problem reprojecting a SHP
>> From: mattslists at gmail.com
>> To: gejst5 at hotmail.com; qgis-user at lists.osgeo.org
>>
>> one of the more spatially aware Northern hemisphere people may
>> contradict me but.. if you look at..
>> http://en.wikipedia.org/wiki/File:Datum_Shift_Between_NAD27_and_NAD83.png
>> the amount of shift your seeing looks suspiciously in the range of the
>> difference between NAD27 and NAD83, are you positive your input data
>> are in NAD27 and that your using the correct translations through the
>> process?
>>
>> Your use of "UTM WGS 84" doesn't seem correct. UTM implies an XY
>> coordinate system over a piece of the WGS84 spheroid and you need to
>> specify a zone as well.
>>
>> good luck
>>
>>
>>
>> On Sun, Jun 5, 2011 at 4:32 AM, Gerardo Jimenez <gejst5 at hotmail.com>
>> wrote:
>> > Hi
>> > I have a dxf data whose coordinates are in UTM Nad27 zone 14q (14N for
>> > any
>> > GIS). I  reproject the data to UTM WGS 84 either with vector tools or
>> > save
>> > as options and data I have from a GPS do not match my vector layer. I
>> > posted
>> > this  also in the forum and followed the advise of building a KML from
>> > my
>> > original data.  Same thing. I made an experiment, same dxf, exported to
>> > shape, define UTM nad27 projection, and reproject to UTMwgs84 and build
>> > a
>> > kmz in ArcMap. QGis and ArcMap Nad 27 data do match perfectly. The wgs84
>> > data from QGIS and Arc Map differ about 80 meters (considerably if you
>> > want
>> > to use a vector layer displaying the streets of an entire city the size
>> > of
>> > Mexico City). The kmz from arcmap looks better in Google earth (streets
>> > do
>> > match better, not perfectly but better, the sat image) the the kml
>> > produced
>> > by QGis. So I wonder if anybody knows if I am doing something wrong or
>> > if
>> > the projection tools available in Qgis are working well.
>> > For those interested I Include the experiment in the following file
>> >
>> > http://hotfile.com/dl/119748524/923a1a6/Prueba.zip.html
>> >
>> > Thanks before hand
>> >
>> > Gerardo Jiménez Delgado
>> > Instituto de Investigaciones Antropológicas
>> > Universidad Nacional Autónoma de México
>> > Ciudad Universitaria s/n
>> > Coyoacan 04510 Mexico City
>> > Mexico 56 22 95 16
>> >
>> >
>> > _______________________________________________
>> > Qgis-user mailing list
>> > Qgis-user at lists.osgeo.org
>> > http://lists.osgeo.org/mailman/listinfo/qgis-user
>> >
>> >
>