The UTM Easting and Northing are the following:
X = a*L ,
Y = a * tan^-1(sin(F)) - a*e * tan^-1(e*sin(F))
For the Web Mercator the same equations are:
X = a*L,
Y = a * tan^-1(sin(F))
What's going on here? The Web Mercator as a projection is treating the
Earth as being a perfect sphere. On t
Am 18.05.18 um 22:30 schrieb Nicolas Cadieux:
Hi,
NAD27 does touch the northern part of South America but you are correct
in saying that it does not extend in Brazil.
Note that +datum=NAD27 redirects to the US/Canadian grid shift files
which do not even cover Central America.
See
https://g
Hi,
NAD27 does touch the northern part of South America but you are correct
in saying that it does not extend in Brazil. I wrote the comments when
I was still trying to figure out where the maps were in the world. I
often get problems with NAD27 vs NAD83 grid in Canada as many maps have
bee
> Le 18 mai 2018 à 00:28, a écrit :
>
> I haven't been able to open the dataset but going through the discussion I
> would like to offer some assistance since I believe there are some
> misconceptions here:
>
> First, the data has nothing to do with the NAD27 / NAD83 datum's since these
>
Hi Carlos:
I georeferenced 2 screen shots of your maps and obtained good results.
I would have a close look at the coordinates of your ground control
points and make sure you selected the utm grid intersection as a control
point versus the corner of the mapsheet which is a lat/long grid. It i
I haven't been able to open the dataset but going through the discussion
I would like to offer some assistance since I believe there are some
misconceptions here:
First, the data has nothing to do with the NAD27 / NAD83 datum's since
these are North American datum's and they don't apply I believe
Thanks for the input Nicolas
These are official maps so the utm grid is ok. I figured that I was using a
linear transformation, with the option to just create the world file, which
works for control points at the corners (lat/long), since the boundaries of
the map is defined by latitude/longitude.
Hi,
The utm grid is way off or we have the wrong epsg code. If you geofence using
2 points (linear algo) using a service like google earth, you will see the
distortion. The long lat coordinate are probably ok but I did not test them.
You can either use the long lat or use more points. With 4
Hi,
I am looking at your maps now. If I understand, it works with lat long but not
the UTM Coordinates. It could be a mistake in the utm grid. Perhaps one utm
grid is in NAD27 and the other in NAD83. That could explain the shift.
I will look at it.
Nicolas
> Le 17 mai 2018 à 12:42, Carlos
When using the georeferencer some of the methods require at least 3 points,
even though you might think it not necessary. Otherwise you can get unusual
results.
Steve
--
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___
Qgis-us
Thanks Nicolas, but the misalignment still persists. OTF is off, project
has same CRS as data (epsg 29192). There is a ~400m difference in the N-S
direction.
Carlos
On Thu, May 17, 2018 at 1:28 PM, Nicolas Cadieux <
nicolas.cadi...@archeotec.ca> wrote:
> Hi,
> Disable projection on the fly. Mak
Hi,
Disable projection on the fly. Make sure the project is in the same CRS as
your maps.
Nicolas
> Le 17 mai 2018 à 12:14, Carlos Henrique Grohmann de Carvalho
> a écrit :
>
> Hello all
>
> I have two pngs of topographic maps from southeastern Brazil (a zip file with
> images and points is
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