[Qgis-developer] Regarding linear transformation in Georeferencer

[Siki Zoltan]

Dear Sajid,

checking the source of the plugin I realized that different scales are 
used in easting and northing direction. So the formulas look like:
E' = Eoffset + Escale * E
N' = Noffset - Nscale * N

The minus in N formula is because of the different axis direction in the 
screen coordinates and map coordinates.
The four unknowns are calculated from a least squares estimation.

Regards,
Zoltan

On Wed, 13 Aug 2014, sajid pareeth wrote:

> Hi Zortan
>
> Thank you for the reply.
>
> Would be great to know, how this Offsets and scale is calculated from a set
> of GCP's.
> Any idea?
>
> Regards
>
> Sajid
>
>
> On Wed, Aug 13, 2014 at 3:30 PM, Siki Zoltan <siki at agt.bme.hu> wrote:
>
>> Dear Sajid,
>>
>> linear transformation (from my practice) use three unknowns
>> offset (Easting, Northing) and scale. No rotational angle.
>> The linear is not a good name for it.
>> E' = Eoffset + scale * E
>> N' = Noffset + scale * N
>>
>> Zoltan
>>
>>
>>
>> On Wed, 13 Aug 2014, sajid pareeth wrote:
>>
>>  Hi,
>>> Can anyone give me hints on statistical background behind linear
>>> transformation in Georeferencer plugin?
>>>
>>> I want to know the formulae used to calculate the residuals while using
>>> linear translation.
>>> Any related paper/material on which it is developed??
>>>
>>> Thanks and Regards
>>>
>>> Sajid
>>>
>>>
>>> --
>>> Sajid Pareeth
>>> PhD Student
>>>
>>> http://gis.cri.fmach.it/pareeth/
>>>
>>> Fondazione Edmund Mach
>>> Research and Innovation Centre
>>> GIS and Remote Sensing Unit/Limnology and River ecology
>>> Via Mach 1, 38010 San Michele all'Adige (TN) - Italy
>>> Phone +39 461 615 669
>>> spareeth at gmail.com
>>> sajid.pareeth at fmach.it
>>> skype: spareeth
>>>
>>>
>
>
> -- 
> Sajid Pareeth
>
> http://gis.cri.fmach.it/pareeth/
>
> Fondazione Edmund Mach
> Research and Innovation Centre
> GIS and Remote Sensing Unit/Limnology and River ecology
> Via Mach 1, 38010 San Michele all'Adige (TN) - Italy
> Phone +39 461 615 669
> spareeth at gmail.com
> sajid.pareeth at fmach.it
> skype: spareeth
>