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changing projection from Lambert to Mercator

irenegobran Global Mapper UserTrusted User
edited June 2012 in Projection Questions
I need to change several georefrenced tiff files from RGF/Lambert93 to Mercator /wgs84.the problem is I have 50 cm image resolution and when I change projection ,I find in the tfw files that the resoluton has changed to 73 cm.Is that normal? thanks!


  • global_mapper
    global_mapper Administrator
    edited June 2012
    Where are you seeing the resolution reported and how are you changing the projection? By default the export in a new projection should maintain the original resolution, but keep in mind that the Mercator projection is very distorted in the X direction when far from the equator (like in France) so the size of a pixel in ground units (Mercator meters vs. RGF meters) could be different. What matters is the projection-independent distance across the pixel reported by the distance tool and not the distance in projection (grid) units when using a very distorted projection like Mercator.


    Global Mapper Guru
  • irenegobran
    irenegobran Global Mapper User Trusted User
    edited June 2012
    I see the resolution in the tfw file ,I am using batch convert/ reproject option
    If i keep the option resolution as input ,I have 73 cm in the tfw ,if i precise 50 cm ,I have 50 cm but when I want to redo the reprojection from mercator to Lambert93 ,i have insted of 50 cm -38 cm.
    It seems as you have answered ,there is a lot of distortion!

    Global Mapper Guru[/QUOTE]
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