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i use two different ways to project lat lon data taken from google earth to ITM (Israel Transverse Mercator) and export the data to arcmap
same ways i try to unproject ITM data and export the data to google earth
both ways i get a deviation of about 90 m
first way: cs2c2
- cs2cs +proj=longlat +ellps=WGS84 +datum=WGS84 +to +proj=tmerc +lat_0=31.73439361111111 +lon_0=35.20451694444445 +k=1.000007 +x_0=219529.584 +y_0=626907.39 +ellps=GRS80 +units=m file.txt>output.txt
second way: DNRgarmin : i downloaded DNRgarmin open a shp file or a kml file and try to convert it
both ways i get a deviation of about 90m does anyone have an idea wht i am doing wrong?

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up vote 1 down vote accepted

You almost certainly need to add a datum transformation to the cs2cs definition. I would try

+towgs84=-48,55,52

which is listed as having approximately 2m accuracy in the EPSG Geodetic Parameter Dataset. Another possibility is the following, but I am not sure of its provenance (including its accuracy):

+towgs84=24.0024,17.1032,17.8444,-0.33009,-1.85269,1.66969,-5.4248

Note: ITM uses the Israel GeogCRS (aka datum) which is based upon the GRS80 ellipsoid, but that doesn't mean that the Israel datum is the same as WGS84.

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thank you it seem to work –  eliavs Mar 19 '13 at 6:20
    
and when i am transforming the other way, from ITM to lanlon? –  eliavs Mar 20 '13 at 12:04
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It should still work because the transformation is defined as being from "other" datum to WGS84. The software will know how to apply when transforming from WGS84. –  mkennedy Mar 20 '13 at 14:27
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