How to convert 6 & 7 digit coordinates to degrees latitude & longitude

Question

I'm a bit new to the whole GIS world, and though I am making great headway drawing polygons and such in Bing Maps, I am currently stuck. In our SQL spatial data, I came across MULTIPOLYGON data, where all the coordinate values are very large numbers (6 digits and 7 digits for what should be latitude and longitude, before the decimal). I found an SQL method to dismantle the multi-polygon into several polygons, but those large values do not work in Bing Maps nor Google Maps. So I've been searching for an algorithm to convert those large numbers down to what I have perceived as regular latitude/longitude numbers, such as 45.19167 -93.58328 (which does work on online maps).

With that said, could somebody please either show me or point me in a great direction to learning how to convert 631456.83, 3816200.79 to something I can use online. I know the coordinates fall somewhere in Arizona.

Answer 1

Your coordinates are likely in UTM (Universal Transverse Mercator) Eastings and Northings.

You can convert UTM coordinates to lat/long online using many different sites. Here in one. You can also perform this calculation in excel or inside of a database if you can work out the formula. Alternatively you can perform the conversion inside of a GIS such as QGIS or ArcGIS.

Before you can convert coordinates to lat/long you will need to know which UTM zone your coordinates fall in.

Here is an example for North America:

In this example, most of Florida falls within the UTM zone 17N.

I came across this page by searching 'batch convert UTM to lat/long'.

Answer 2

Try this one:

http://cs2cs.mygeodata.eu/

or use "proj" (command line below assuming UTM zone 17 south and wgs84):

# geographical coordinates (ie. longitude,latitude) to utm
proj -f "%.4f" +proj=utm +zone=17 +south +ellps=WGS84 < myfile

# utm to geographical coordinates (ie. longitude,latitude)
proj -f "%.4f" +proj=utm +zone=17 +south +ellps=WGS84 -I < my file

In your case (ie, 631456.83356859628, 3816200.7961099017; which are Easting and Northing UTM coordinates respectively as METERS) you need to know the utm ZONE and HEMISPHERE (something like ZONE 17 SOUTH above). Your data should likely be in WGS84.

In the end if you don't know the UTM zone you are, I would simply loop over the USA UTM zones (ie. 10-19) to get the geographical coordinates, and then plot the resulting coordinates to see which are the correct ones:

for ((utmZone=10;utmZone<20;utmZone++))
do
  echo 631456.83356859628 3816200.7961099017 | proj -f "%.4f" +proj=utm +zone=$utmZone +north +ellps=WGS84 -I
done

getting:

-121.5685       34.4790
-115.5685       34.4790
-109.5685       34.4790
-103.5685       34.4790
-97.5685        34.4790
-91.5685        34.4790
-85.5685        34.4790
-79.5685        34.4790
-73.5685        34.4790
-67.5685        34.4790

where "%.4f" controls the number of decimals.

Hope this helps,