Exported pixel size when cropping to selected area
mapdaddy
Global Mapper User
Hello
I have been having a problem when I export .tif images that have been cropped to a selected area.
The exported pixels size does not match the pixel size I specified in the export dialogue. For example if I specify .2m pixel I will get .1999999 or .200001 this doesn't seem like much but if my image is 4000 pixels wide I end up missing a column/row or with an extra column/row.
The area I am cropping to is square, the upper left corner is on even pixel in the original image and the size of the area should fit a even number of pixels.
I have been having a problem when I export .tif images that have been cropped to a selected area.
The exported pixels size does not match the pixel size I specified in the export dialogue. For example if I specify .2m pixel I will get .1999999 or .200001 this doesn't seem like much but if my image is 4000 pixels wide I end up missing a column/row or with an extra column/row.
The area I am cropping to is square, the upper left corner is on even pixel in the original image and the size of the area should fit a even number of pixels.
Comments
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Do you have the option checked in the Advanced section of the General tab of the Configuration dialog to maintain the export bounds over the sample spacing? If that is checked and there is any difference in the multiple this could happen. Also you might check the option there to keep an export pixel if any part is in the export crop area in case any of the export pixel centers fall just outside the crop area bounds or something but a corner is in them.
Thanks,
Mike
Global Mapper Guru
geohelp@bluemarblegeo.com
Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation -
I don't have the maintain export bounds over sample spacing option checked but I do have the keep export pixel if any part inside crop area option checked.
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Which version of GM are you using and where are the sample spacings being reported? Are you exporting out to a new GeoTIFF format or something else? I'm wondering if there is just a rounding issue in the precision of the stored spacing or something.
Thanks,
Mike
Global Mapper Guru
geohelp@bluemarblegeo.com
Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation -
I am using v12.2 64bit
There does seem to be some kind of rounding issue. The GM metadata window and arcgis properties show the pixel size as .2. The tfw created by GM and arcgis show the pixel size to be .200000000001
When I overlay my cropped image on top of the original and zoom way in. I can see that the pixel size is actually slightly different. -
Can you get the latest v15 trial from Global Mapper Downloads and see if it shows the same thing? You can request a trial from the registration dialog and then try the export.
Thanks,
Mike
Global Mapper Guru
geohelp@bluemarblegeo.com
Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
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