A few days ago I was talking about the georeferencing of Images downloaded from Google Earth, using the kml as reference when stretching. Testing Global Mapper I realize that this step can be avoided if we download the calibration file at the moment of downloading the image, by the way we can also convert it to another format like ECW which is very light and does not lose quality or even kmz as an image.
1 Download the calibration file
For this, at the moment of downloading the image, it is necessary to select to save the file in Global Mapper format.
When downloading the image, in the same directory will save a file, with the same name of the image and with extension .gmw
2 Open the image
To open it in Global Mapper, we do File> Open Data files ...
We did not choose the .jpg image but the .gmw file, in step we are going to bring the already georeferenced image.
Eye, that unless we are going to work with geographic coordinates, the image must change of projection because when descending from Google Earth it comes in Latitude / Longitude and Datum WGS84.
This WGS84 Datum that uses Google is quite similar to the ETRS89 that is used in Europe or the Clarke 1866 that we use in America.
But suppose we want to switch to a different Datum, as in the case of ED50 or the NAD 27 that is quite similar and very widespread in America).
3 Change the projection of the image
This is done in:
In the Projection We lift a panel like the one shown in the image:
If we want to pass a projected system we do it in the combobox Projection.
In this case we are interested in moving to UTM. Then we chose the area, Datum and units.
You can also assign an EPSG code directly, load a .prj file that was quite frequent with ArcView 3x or a .aux that already has an xml structure in the new versions of ESRI. Even if you have another file built with xml nodes in another program, it can be loaded using the .txt extension
Then press the button Appy. In the lower status bar we should notice the change.
3 Export it to ecw
In this Global Mapper does not stop surprising, because to pass images to .ecw format is something that many programs do not. Because it is owned by Erdas, you must have your authorization, in the case of Microstation Up versions V8i does.
File> Export Raster / Image format ...
Notice that you can switch to binary formats, as well as Idrisi, TIFF or Erdas img.
An ecw image can be very useful for use in a CAD / GIS program but if we want to call it to Google Earth it is not possible to bring it georeferenced unless we export it to Global Mapper to a kmz that contains the image.
4 Export the image to kmz
Generally we have understood by a kml a vectorial file that contains some lines, points or polygons, weighing only a few kb.
In case of exporting it to kmz the program begins to do a number of iterations in which the image starts in segments and makes an index in a kml, such that when opening the kmz in Google Earth what it brings is the image.
To see what's inside a kmz, the extension is changed to a .rar / .zip compressed format and then unzipped into a folder. There you can see that there is a file called doc.kml that contains type elements in its structure region And with the image called as Groundoverlay.
Very good the Global Mapper, I bet that this last action does not do any program.