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Author Topic: Coordinates in M4OPS  (Read 305 times)

PeterC

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Coordinates in M4OPS
« on: 14 January 2017, 15:41:04 »
Projections are about how the three dimensional earth is represented in two dimensions, and they can get very complicated; for example:
  • latitude and longitude may be in that order, or in the reverse order
  • they may be in decimal degrees or in metres
  • they may use various places as their zero points
The way I think of it is
  • Longitude is West to East, and in mathematical terms it is the x-axis
  • Latitude is South to North, and in mathematical terms it is the y-axis
  • Geographers tend to put Latitude first, Mathematicians tend to put Longitude first
The possible formats when M4OPS is used to output coordinates are:
NameDescriptionCommentExample, using the centre of Needingworth
No lat/lon clickDoes not generate coordinatesDefaultN/A
M4OPS lon;lat csvLike EPSG:4326 in degrees
but longitude first
Uses semi-colon rather than comma
generally used for input into M4OPS
-0.0322822;52.3304203
M4OPS parametersIn degreesIn a format suitable to append to a URL&Lon=-0.0322822&Lat=52.3304203
lat,lon csvLatitude first, in degrees'EPSG:4326'52.3304203, -0.0322822
{lon,lat} GeoJSONLongitude first, in degreesIn computer friendly GeoJSON format[-0.0322822, 52.3304203]
EPSG:3857 (x/y)Longitude first, in metresUsed internally within M4OPS-3593.9420062, 6860091.7465739
DegMinSec N/ELatitude first
Northing and Easting
Traditional degrees
minutes and seconds
52° 19′ 50″ N 0° 01′ 56″ W
GeoHack linksOpen a GeoHack windowShows many mapping,
aerial, wiki, photo
and other resources
GeoHack link

Note that, in case it is used for very local mapping, M4OPS outputs 7 decimal points, which for degrees is about 1 cm - the practical limit of commercial surveying (https://en.wikipedia.org/wiki/Decimal_degrees)

If you want to locate a place in M4OPS that you have found in Google Maps, then the easiest process seems to be:
  • in Google Maps zoom right in to the place you are interested in
  • in your browser's address bar locate a string like /@50.9635263,-4.2593133,15z/ (note the 15z may be 16z or 17z - it is the zoom
  • copy the part of this string between the /@ and ,15z/ (ie 50.9635263,-4.2593133) - these are the coordinates of the bottom left of the window
  • in M4OPS click on the Go to button at top right
  • paste in the coordinates you have copied and M4OPS should move to the specified location
  • (Hint: using the Bing Aerial with Labels layer you can see the names of places to check you are where you expect to be)

For more on projections and other mapping subjects see the links in Useful background on Web Mapping.
« Last Edit: 19 January 2017, 07:34:11 by PeterC »

 

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