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PHOTOGRAPHY

a) updated by Ken Thompson Nov 2019  GOOGLE EARTH: Google Satellite Map Downloader

With the current high cost of accessing commercial photography this is now a very good option. Using Google Satellite Map Downloader enables you to get a good quality image that you can use in OCAD. To be useful you need to pay about $A30 for a licence. The freeware version defaults to a zoom level of 13 which is not adequate for most purposes. With the licence you usually get a zoom level of at least 18. It pays to experiment however. With two recent maps I have been working on I got a zoom level of 20 but errors appeared when I tried 21 or 22. The resolution at 20 was very good however and I suggest you start with this setting.

I have re-written this section using a hopefully easier to follow step by step approach

  1. Load Google Earth and set coordinates to show in decimal degrees. To do this go to Tools -> Options and select Show Lat/Long Decimal Degrees
  2. Record the following boundaries of the area you wish to use. Left Longitude, Right Longitude, Top Latitude, Bottom Latitude. Take care that you do not select too large an area or Google may block your IP for a day or so!
  3. Load Google Earth Satellite Downloader and enter the above coordinates.
  4. Click Download.
  5. Go to Tools -> Combine images. This will combine all the tiles into a single bmp file.
  6. By default the programme produces a 16bit bmp file as well as a world file containing the coordinates. The 16 bit file is not supported by OCAD so load it in a graphics programme and save as a standard 24bit Windows bitmap. Alternatively you can save the file as a jpg or tiff file. Best quality retention, however is achieved with a bitmap file. If you would like to learn more about world coordinates files try this link provided by Peter Hoban: http://www.cryer.co.uk/file-types/t/tfw.htm  
  7. The world maps generated by this programme are not compatible with OCAD. The good news is that Peter Hoban (The cool climate in Tasmania must generate lots of good ideas!) has developed a spreadsheet, based on the wisdom of many others he tells me, that will convert the associated world file into a file that is compatible with OCAD 10 & above. What is involved is described below by Peter. I have tested the process with already accurately calibrated maps & found the spreadsheet conversion to be very accurate within the limitations of Google Earth itself. The converter is protected except for those cells into which you are required to paste data.  The protection is only for convenience - the password is blank (no password)".
  8. (this part provided by Peter Hoban) "Google Earth uses decimal degrees to locate their images, so the Google Satellite Maps Downloader will use these also.  Experiment showed that this too is the unit of the scale factor.  Conversion of those coordinates to say a UTM grid based on WGS84 or anything more recent is not easy and may be beyond them.  (The more recent coordinate systems differ from WGS84 by only a few centimetres.  WGS84 is also the default UTM coordinate system for every GPS I have ever used.)  The coordinates provided are those for the top left corner of the image. When you make a map in OCAD you are able to create a world coordinate system and this expects a UTM system like WGS84. In order to get the downloaded Google images to open correctly located and scaled in OCAD it is necessary to convert the world file to  appropriate UTM units.  I have managed to make (largely copied from the work of others) a spreadsheet to do this. The Converter zip file contains both an open office & excel version of the spreadsheet: 
  9. Load the bmw world file using right click -> edit. This file should be found in the same location as the bmp file saved above.
  10. At the same time as 7 open Coordinator Converter in Excel or Open Office.
  11. Copy existing settings into INPUT CELLS  (left side) on spreadsheet. The right box will then have your converted data in WGS84 UTM coordinates.  Note that the scale factors should now be about equal (within 1%).  Copy the converted data back to the originally named .world file.
  12. The image should then open correctly located and scaled in your OCAD map. 

b) A variation of the above using Georeff (notes & programme kindly made available by Mark Roberts)

I have written some software to replicate the spreadsheet above and automate this task; it is called Georeff as an homage to the mapper who mentioned it to me. You can find it here:

 http://www.organisedgrime.com.au/Georeff/publish.htm

  Optionally use Georeff / Make to generate the GSMD file

 -          View the area in Google Maps

-          At the NW extent, right click and select “Directions from here” and the lat/long will be displayed, if not, keep trying

-          At the SE extent, right click and select “Directions to here” and the lat/long will be displayed, etc

-          Click outside the map, then Ctrl-A to select everything, Ctrl-C to copy (you are copying the text that says “We could not calculate directions...”)

-          Launch Georeff, select Make,

-          Ctrl-V to paste into the window on the left

-          Now save the file somewhere

 Now use GSMD using the GSMD file; Combine the Images to create a bigmap.bmp; (This does not always work.)

 Go back to Georeff and use File / Open, Calculate and convert, selecting the bigmap.bmp; it will creat a georeferenced JPG for you.

 

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