[GIS] What kind of coordinate system is this

coordinate systemcoordinateslatitude longitude

I have a csv with a list of the world sea ports and their coordinates.

The coordinates are in this format:

5234N 00226W

How can i convert this to decimal Latitude / Longitude ?

Data source

Best Answer

Seems to be http://en.wikipedia.org/wiki/UN/LOCODE

Coordinate syntax explained in http://www.unece.org/fileadmin/DAM/cefact/locode/Service/LocodeColumn.htm#Coordinates

1.10 Column "Coordinates"

This column contains the geographical coordinates (latitude/longitude) of the location, if there is any.

In order to avoid unnecessary use of non-standard characters and space, the following standard presentation is used:

0000lat 00000long

(lat - Latitude: N or S ; long – Longitude: W or E, only one digit, capital letter) Where the last two rightmost digits refer to minutes and the first two or three digits refer to the degrees for latitude and longitude respectively. In addition, you must specify N or S for latitude and W or E for longitude, as appropriate.

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Coordinate System – What Does Coordinate System WG 21° Mean?

I think that Hartebeesthoek94 / Lo21 EPSG:2049 fits best. I added the constant 3700000 to the X values as mentioned in the header, and imported the coordinates as delimited text into QGIS. This is what I get:

enter image description here

The coordinates are west of 21°E and south of the equator. Exporting the coordinates as WGS84 results in:

"0","20.0777332087","-33.9376197503","A","85267.05","3757125.26"
"1","20.0780827565","-33.937511304","B","85234.84","3757112.94"
"2","20.0784080105","-33.9373687785","C","85204.91","3757096.86"
"3","20.0788528052","-33.9371936109","D","85163.96","3757077.06"
"4","20.0793019671","-33.9369340943","E","85122.69","3757047.9"
"5","20.0793436801","-33.9369675812","F","85118.8","3757051.58"
"6","20.0982437624","-33.937447055","801","83370.88","3757089.25"
"7","20.0956436897","-33.9410931123","8P1","83607.71","3757495.81"

Columns 2 and 3 should give you the East and North coordinates that Google can understand.

Coordinate System – Convert Over 360 Degree Range to +/-180 Longitude in R

The data goes from 20 to 420, which is including some areas more than once because the metadata says:

NC_GLOBAL#NOTE2=Longitude extends from 20 E to 420 E to avoid a break in major ocean basins. Data repeats in overlap region.

So we need to split the data into the 20 to 360 section and the 360 to 380 section and put that 360 to 380 section on the left of the 20 to 360 section. We don't need 380 to 420 because that's overlap.

So...

library(raster)

define two extents to cut the raster with. The "Y" extent just has to be bigger than the raster so I go up to 90:

e1 = extent(c(xmin=20,xmax=360,ymin=-90,ymax=90))
e2 = extent(c(xmin=360, xmax=360+20, ymin=-90, ymax=90))

Load the raster - I'm loading just the "vm" layer, you'll have to repeat over the others:

d = raster("./oscar_vel7001.nc",varname="vm")

Now split the bits that we want using the extents:

d1 = crop(d,e1)
d2 = crop(d,e2)

Next shift the bit on the right to fill the space from 0 to 20:

xmin(d2)=xmin(d2)-360
xmax(d2)=xmax(d2)-360

merge will paste the two parts together, giving us a raster from 0 to 360, and rotate will shift it to be -180 to 180:

dm = rotate(merge(d1,d2))
plot(d)
plot(dm)

shows the original shifted overlapping map and the corrected -180 to +180 map:

Best Answer

Related Solutions

Coordinate System – What Does Coordinate System WG 21° Mean?

Coordinate System – Convert Over 360 Degree Range to +/-180 Longitude in R

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