Location From Google Maps

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Here's a technique for determining your precise location using Google Maps and Topocoding.com.

The very short version (recommended):

  1. Use the Stellarium Location Helper, a Google Maps/Topocoding mash-up I've put online, and copy the data to the Stellarium Location dialog.
  2. There is no step 2 :-)
    (But see step 11 in the long, manual version below if you find that the Location dialog gives you a hard time.)

The short, manual version:

  1. Extract latitude and longitude from the Google Maps permalink URL (it is contained in the ll query parameter - that is two lower-case L's for latitude/longitude. The first number is the latitude in decimal notation, the second number is the longitude.)
  2. Use a tool such as the FCC latitude/longitude converter to convert decimal to degrees/minutes/seconds, replacing +/- signs with N/S (for latitude) or E/W (for longitude)
  3. Use topocoding.com to determine the altitude.
  4. Copy-and-paste the data into Stellarium's text fields

The long, manual version:

  1. Navigate to your location using Google Maps
    1. Open Google Maps in your browser (or open a localized version of Google Maps if you prefer, such as Google Maps Germany).
    2. Navigate to your location. For example, enter your address such as: 8-10 rue Mario Nikis, 75738 Paris Cedex 15, France
  2. When your location is in the center of the Google Maps display, copy the permanent URL of this location to the clipboard
    1. Find the hyperlink (blue, underlined text) labelled Link in the top right corner of the Google Maps page. It should have a symbol of a little chain next to it.
    2. Right-click that link and choose Copy Link Location (Firefox) or use the equivalent menu item in other browsers
  3. Paste the URL into a text editor
    1. Open a text editor such as TextEdit (Mac OS X), Notepad (Windows), or Kate (KDE).
    2. Use the text editor command to paste the URL - e.g. use the Edit->Paste menu item, or press Ctrl+V on Windows or Linux, or Cmd+V on Apple
  4. You should now see a URL looking something like this:
    http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=8-10+rue+Mario+Nikis,+75738+Paris+Cedex+15,+France&sll=37.0625,-95.677068&sspn=35.821085,79.101563&ie=UTF8&ll=48.848663,2.304533&spn=0.007272,0.019312&z=16&iwloc=addr
  5. Find the part beginning with &ll= until the next ampersand (&). (Don't confuse ll with sll!) That part should contain two numbers separated by a comma, shown highlighted here:
    http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=8-10+rue+Mario+Nikis,+75738+Paris+Cedex+15,+France&sll=37.0625,-95.677068&sspn=35.821085,79.101563&ie=UTF8&ll=48.848663,2.304533&spn=0.007272,0.019312&z=16&iwloc=addr
  6. The first of these numbers is your latitude in decimal notation; the second is your longitude. In this example, the latitude is 48.848663 and the longitude is 2.304533.
  7. To convert these numbers into degrees/minutes/seconds, the notation expected by Stellarium, head over to the FCC latitude/longitude converter
    1. In the second box on that page - labelled Decimal Degrees to Degrees Minutes Seconds - enter your latitude next to Enter Decimal Latitude and your longitude next to Enter Decimal Longitude. (Use copy-and-paste to avoid typos.)
    2. Press Convert To Degrees Minutes Seconds.
    3. Read out the latitude and longitude next to Result. For this example you would get 48° 50' 55.1868" and 2° 18' 16.3188".
  8. Next, convert +/- notation to N/S E/W notation.
    1. The result you got from the FCC uses plus/minus signs to show which hemisphere the location is on - actually it only uses the minus sign, if the result is positive then the plus sign won't be shown. Stellarium, however, requires directions (N/S for latitude, E/W for longitude) so you'll have to tweak the result a litle.
    2. If latitude starts with a minus sign, remove the minus sign and add S for South followed by a space in front of it. Otherwise, add N for North followed by a space.
    3. Likewise, if longitude starts with a minus sign, remove the minus sign and add W followed by a space in front of it. Otherwise, add E followed by a space.
    4. In this example, you would end up with N 48° 50' 55.1868" for latitude and E 2° 18' 16.3188" for longitude.
  9. You now have the latitude/longitude information in the format that Stellarium requires. You can double-check that you've made no mistakes so far by putting the final values back into Google Maps like this: N 48° 50' 55.1868" E 2° 18' 16.3188". The location shown should be pretty much the same location for which you copied the permanant URL in step 2. Compare to 8-10 rue Mario Nikis, 75738 Paris Cedex 15, France - and allow for a few meters of difference due to precision loss.
  10. Now for determining the altitude.
    1. Head over to topocoding.com.
    2. Pop in your latitude and longitude in the text fields labelled Latitude and Longitude. It doesn't matter which format you use, any seems to work - when in doubt, use the original decimal notation.
    3. Press the Add point button.
    4. A tool tip will pop up in the map display showing your altitude in both meters (m) and feet (ft). Copy-and-paste the altitude in meters somewhere.
  11. The latitude, longitude and altitude values you've got now can be copied-and-pasted into the text boxes in Stellarium's Location dialog. In this example, the final values are N 48° 50' 55.1868" and E 2° 18' 16.3188" with an altitude of 45 m. Because the Location dialog is somewhat idiosyncratic, I recommend to follow these steps:
    1. First off, ensure that for Planet you've selected Earth (duh!)
    2. Then choose your country from the drop-down list.
    3. Now enter the name of your location into the Name/City text field. It doesn't hurt if you put in the full location including street name etc.
    4. Ensure your computed latitude is in the clipboard (by copying it).
    5. Select all the text in the latitude text field and press Ctrl+V (Windows), Cmd+V (Apple) or the appropriate key for pasting your computed latitude. Then press Enter to ensure Stellarium registered the new value.
    6. Note that Stellarium is quite unforgiving when it comes to latitude/longitude. For example, if the latitude doesn't start with N or S, or doesn't end with a quote sign (") it won't be accepted properly and you won't get an error message if it's wrong. So be careful to copy the correct and full value.
    7. Follow the same procedure for the longitude text field.
    8. Fill in the altitude that topocoding.com gave you.
    9. Press the Add to list button. This will store your location permanently and also update the location display on the world map. Double-check that the red pointer shows the correct location.
    10. Finally, tick the Use as default checkbox and close the Location dialog.
    11. If something went wrong, select the new location in the Location dialog, press the Delete button, and start over. (The Delete function doesn't always seem to work, though.)
  12. Phew, you're done - enjoy your precisely calibrated Stellarium!
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