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Google Earth 

Warning:

Google Earth in AirPhotoSE uses the Google Earth Web Browser Plugin. The plugin is installed automatically when you install the normal Google Earth client. Do not install the plugin without the Client, or some database functions will fail. 

Open Google Earth either by clicking on:



on the main toolbar or:



on the File Menu, and there selecting Google Earth.  The usual Google Earth Globe will appear after some delay if the machine has an active Internet connection.  If not, a warning will appear telling you that there is no connection to the Internet. Depending on how busy Google's servers are, this may take a considerable time.



On the menu bar of the Google Earth window:



you will see a few options. Initially, click on Action to choose one of six main actions:



Find by Name permits a Google Earth search on a placename.  If there is ambiguity because the same name may be in different countries, add a country descriptor as well:   See FindbyName:



FindinGPS will show an image file opening dialogue.  If an image listed contains GPS data in its EXIF file header, then clicking on the file name will show the area in Google Earth at the recorded values of GPS latitude and longitude coordinates. 

Find in Grid displays a grid dialogue permitting entry of desired coordinates in the grid chosen previously in Options setup. For example, with EPSG chosen, you may see:



and with UTM-WGS84 you may see:



The Trigonometric Points option shows a page with Internet links to the national mapping agencies in various countries which have published lists of visible trigonometric points on the Internet.  The data from such points is not standardised, so you must open the Web site concerned, search for a point of interest in the chosen grid system. Then copy and paste the latitude and longitude into the FindinGrid search dialogue to see the point displayed at the centre of an image if it is visible in Google Earth.  This point can be used for refining the calibration of Google Earth image data in it's immediate neighbourhood by adding it with manual calibration.



When you close the Google Earth Window via the Return Show Images menu entry



the result is automatically calibrated in the datum of the grid you have chosen in AirPhotoSE.  If you want to superimpose the GE result on a map however, you must first align the result to the chosen grid.  This is not necessary only if you have chosen WGS84 UTM as your grid, since that is compatible with the latitudes and longitudes used in Google Earth.

Depending on the speed of your Internet connection and how busy the Google Earth image servers are at a given moment, it takes some time for each image tile to stream to your machine.  The programme waits for a time equal at most to the setting of Maximum Delay for the image to sharpen while the Google Server stream blocks of data to make the complete tile.  The setting of Minimum Delay slows down the advance of tiling to give the Google Earth server time to make a sharp image.  Usually, the default values (shown in milliseconds) will be sufficient, but if a part of an image result is unsharp, increasing the Minimum Delay will usually help. When the Maximum Delay value has been reached, a warning will be issued and you will be asked if you wish to continue anyway.  Normally, you should answer "No" and then raise the Maximum Delay time.  



The Test option displays an area with straight field boundaries and roads for manual calibration testing with the line intersection option.  The geographic coordinates shown may be changed to display a different area.



Contents displays this help and offers a table of contents for other topics in the AirPhotoSE help file.



The About option displays a dialogue box giving information about the Google Earth plugin currently installed on your machine.



Note: 

Install or update to the latest version of Google Earth even if you have selected automatic updates in Google Earth when installing for the first time, since this does not guarantee that you will have the latest Plugin version. In the AirPhotoSE GE window, clicking on Help, About will display the version that AirPhotoSE is using. This must be at least version 5.2 or historical imagery will not be available.

When you open Google Earth, and if it has installed a plugin version 5.2.1.1588 dated Sep 1, 2010 or later, you may see a "Time Line" slider in the upper left corner of the GE window. However, whether or not this appears may depend on the speed of the Internet connection or the Google servers.  If it doesn't appear, close the GE window with the Don't Show, Return option on the file menu and re-open it.



You can drag on the slider to show Google Earth imagery of the same area from other dates, or you can click on the upper left symbols in the Time Line box to see differently dated imagery. It can be toggled on and off with the TimeLine entry on the menu.



When you are satisfied with the position and altitude of the GE image, click on the Save As option on the main menu.  A dialogue box will open showing any previously saved images and permitting you either to write a new one with a new name to disk or to overwrite a previously saved image.  You can also choose the type of image saved. 



You may repeat this operation as many times as you wish with different locations, parameters and other options. 

When you have finished:

On the File menu,



Clicking on Return, Show images will open and display all files saved when the Google Earth Window closes.  They will be automatically calibrated in the chosen grid, but they are not aligned to that grid. They must be aligned in AirPhotoSE for overlaying on maps.  

A GE image opened in AirPhotoSE after saving and closing the GE Window will show it's central calibration point in the grid you have chosen in Options-Setup or in the EPSG selection window. Nearly all saved images are automatically calibrated in the chosen grid, however some of the grids available in the EPSG database do not contain the data needed, and automatic calibration will fail.



You can move about in the GoogleEarth image, dragging with the right mouse button and zooming with the mouse wheel until you have positioned an area of interest.



When you choose Return, Show Images, the Google Earth selected image will be shown, and if you wish, you may write the currently selected grid over it for precise localisation of site features:



Coordinates and Georeferencing:

Images from GoogleEarth are normally aligned to a spherical version of the WGS84 datum when they are saved and if UTM, Decimal latitude/longitude or Degrees are chosen in Options-Setup, the coordinates of any point will be displayed on the status line when the mouse is moved.  If an EPSG grid has been chosen and the area from GoogleEarth is within the boundaries of that grid, the image will be calibrated using the chosen grid.  Many grids use ellipsoids and datums which differ from that used by GoogleEarth, so that if you using the option on the calibration menu for displaying a grid:

 

the grid will be at an angle relative to the sides of the image:



This will cause misalignment if you overlay a map on the GoogleEarth image.  The option Align to Grid on the Calibration menu will rotate the image so that it is aligned correctly:

 

and can be combined with a map of the area.