[QGIS-Developer] Problem: QGIS Reproject layer Transformation of Lambert North and South Costa Rica to CRTM05

Eduardo Rojas Rodríguez eduardo.rojas at soltig.net
Sun May 7 14:31:39 PDT 2017

Hi everyone!

Before creating a ticket in QGIS Issue Tracking, I wanted to consult you a
few things to be the most effective for when creating the ticket and to
carry all the necessary information.

I wanted to ask who maintains the algorithm "Reproject layer" of QGIS
provider which transformation method is used?

We have detected that in QGIS the transformation of vector layers from the
Coordinate System Lambert North or South for Costa Rica (obsolete official
projection of Costa Rica) to the current Official Projection that is CRTM05
has a transformation problem.

*the problem:* is when use the "Reproyect Layer" to reproject a vector layer
that is in the coordinate system  "Lambert North or South for Costa Rica" to
the coordinate system "CRTM05" a mismatches occurs from 8 meters up to 100 o
300 meters when the process is performed using the "Reproject layer"
algorithm of the QGIS provider in the processing toolbox.

We believe that this is because there is a problem with the Datum transfer
since Lambert North or South for Costa Rica is Local "Ocotepeque Clarke
1866" while CRTM05 is global "WGS84" for that reason we found necessary to
know how the trasnformation is programmed in QGIS for the Reproject Layer

for the transformation we need to know if it is using the matrix of
"Molodensky Badekas" of 3 or 7 parameters, the ideal is that it is carried
out using the one of 7 parameters.

We have the necessary parameters For the matrix of 7 parameters which are: 

Parameters of transformation using the Molodensky Badekas matrix of 7
parameters for reproject CRS:
Ocotepeque 1935 / Lambert Costa Rica South EPSG:5457 and Ocotepeque 1935 /
Lambert Costa Rica North EPSG:5456 to CRTM05 EPSG:5367

PE_PAR_X_AXIS_ROTATION, (-)2.351418791 (Is enough with 4 decimals)
PE_PAR_Y_AXIS_ROTATION, (+)6.1466912E-02(Is enough with 4 decimals)
PE_PAR_Z_AXIS_ROTATION, (-)6.394208994(Is enough with 4 decimals)

These are the parameters for the transformation.

This will be enough to create the ticket in the QGIS Issue Tracking? Or will
more information be needed? Or explain the problem better?

Thanks for the help!

Eduardo :)

Eduardo Rojas Rodríguez
Analista en SIG
Soluciones en Tecnologías
Tel: 506 2505-5453
eduardo.rojas at soltig.net

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