Where is the transformation for NAD27 stored in QGIS?
The transformation for NAD27 is stored in several grid files, which can be found in the proj/share folder and loaded into QGIS. The main source is the conus file for the Conterminous United States:
How to create a.prj file for an image?
The easiest way to create a .prj file for an image is to simply copy an existing .prj file from a shapefile or from the sample .prj files included with ArcPad on the PC (e.g. C:\\ESRI\\ArcPad 5.0.1\\Coordinate Systems).
How to reproject between NAD27 and WGS 84?
I am trying to perform a reprojection for data with datum Nad27 to WGS84 datum. According to AndreJ in some previous questions in Stackexchange ( CRS reprojection for instance) QGIS uses internally by default the ntv2 transformation from NAD27 to WGS84, that should be very exact. I tested with the custom crs calculation tool.
Can a GDAL override a TOWGS84 parameter?
The +datum=nad27 parameter overrides the +towgs84 parameter. GDAL can only do grid shift, or Helmert/Molodensky transformation, but not both. Since the grid is more correct in most cases, the developers decided to skip the 3-/7-parameter transformation if both options are given.
How does QGIS allow you to reproject data on the fly?
QGIS allows you to reproject data “on the fly”. What this means is that even if the data itself is in another CRS, QGIS can project it as if it were in a CRS of your choice. To enable “on the fly” projection, click on the CRS Status button in the Status Bar along the bottom of the QGIS window:
How many datum transformations does QGIS support?
Datum Transformations A Coordinate Reference System, or CRS, is a method of associating numerical coordinates with a position on the surface of the Earth. QGIS has support for approximately 7,000 standard CRSs, each with different use cases, pros and cons! Choosing an appropriate reference