Converting coordinates to ITM with 7 parameters

[Renanel Pickholtz]

Hello,

I am trying to convert WGS 84 coordinates to Israeli new system (ITM) with 7 parameters rather than the simple 3 parameters, but I can't figure out where to add the parameters in the code. 

The parameters are:

X Axis Translation   =  - 24.2204 

Y Axis Translation   =  - 17.2200 

Z Axis Translation   =  - 17.8444 

X Axis Rotation   =  - 0.33009 

Y Axis Rotation   =  - 1.85269 

Z Axis Rotation)    =  1.66969 

Scale Difference    =  5.4248 

I'm currently using the following code to define ITM

> DF.latlong <- SpatialPoints(DF[ , c("LON","LAT")], proj4string=CRS("+proj=longlat +ellps=WGS84")) 

> ITM = CRS("+proj=tmerc +lat_0=31.73439361111111 +lon_0=35.20451694444445 +k=1.0000067 +x_0=219529.584 +y_0=626907.39 +ellps=GRS80 +towgs84=-48,55,52,0,0,0,0 +units=m +no_defs")

> converted.DF <- spTransform(fish.sp.latlong, ITM)

This works but there is still an offset for all coordinates (something that always happens when using the defaults conversion rather than the full 7 parameters above - ftp://ftp.systematics.co.il/GIS/2012/PDF/7p_transformation.pdf).

Anyone? Please help

Renanel

[Michael Dorman]

Hi Renanel,

The additional parameters go into the ITM CRS definition as following. Try using the this definition instead of the one you used in the example -

CRS("+proj=tmerc +lat_0=31.7343936111111 +lon_0=35.2045169444445 +k=1.0000067 +x_0=219529.584 +y_0=626907.39 +ellps=GRS80 +towgs84=-24.002400,-17.103200,-17.844400,-0.330090,-1.852690,1.669690,5.424800 +units=m +no_defs")

Michael

[Renanel Pickholtz]

Worked great!

Much obliged,

Renanel

[Yoni Sidi]

there is a shorter way to do this on the import of the shp file:

library(maptools);

shp_poly <- readShapePoly("file.shp", IDvar = "OBJECTID",  proj4string = CRS("+init=epsg:2039"))

[Michael Dorman]

But this gives the less accurate 3-parameters transformation:

> CRS("+init=epsg:2039")

CRS arguments:

 +init=epsg:2039 +proj=tmerc +lat_0=31.73439361111111

+lon_0=35.20451694444445 +k=1.0000067 +x_0=219529.584 +y_0=626907.39

+ellps=GRS80 +towgs84=-48,55,52,0,0,0,0 +units=m +no_defs

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Michael Dorman
PhD student
Geographic Information Laboratory
Department of Geography and Environmental Development
Ben-Gurion University, Israel

dor...@post.bgu.ac.il

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