Re: [Qgis-user] Problem georeferencing images in UTM

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

Re: [Qgis-user] Problem georeferencing images in UTM

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

Re: [Qgis-user] Problem georeferencing images in UTM

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

Re: [Qgis-user] Problem georeferencing images in UTM

> 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

Re: [Qgis-user] Problem georeferencing images in UTM

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

Re: [Qgis-user] Problem georeferencing images in UTM

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

Re: [Qgis-user] Problem georeferencing images in UTM

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

Re: [Qgis-user] Problem georeferencing images in UTM

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

Re: [Qgis-user] Problem georeferencing images in UTM

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,

Re: [Qgis-user] Problem georeferencing images in UTM

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 -- Sent from: http://osgeo-org.1560.x6.nabble.com/QGIS-User-f4125267.html ___

Re: [Qgis-user] Problem georeferencing images in UTM

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.

Re: [Qgis-user] Problem georeferencing images in UTM

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

[Qgis-user] Problem georeferencing images in UTM

Hello all I have two pngs of topographic maps from southeastern Brazil (a zip file with images and points is available here: https://www.dropbox.com/ s/mexeh4be46pgsk6/images_georef.zip?dl=0) I'm trying to georeference them, but with partial success only. In this image