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Convert coordinates into decimal degrees
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Introduction Original georefenced data often contains sexasegimal coordinates (Degree Minute Seconds). This is actually an heritage from the Sumerians and ancient babylonians
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Introduction Original georefenced data often contains sexasegimal coordinates (Degree Minute Seconds). This is actually an heritage from the Sumerians and ancient babylonians
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Introduction ...while most of time GIS systems requires either decimal degrees, either metric units (UTM). It may be relevant to convert the DMS values into decimals Not all GIS can do this
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1) Parse your data Create 6 extra columns to parse the degrees minutes seconds in separate columns
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1) Parse your data Create 6 extra columns to parse the degrees minutes seconds in separate columns This step can actually be automated by using the Excel function « Find » (to find position of a word in a text) and « Mid » (to extracts elements from words) => this is actually the toughest difficult part of the process are there are no standard solutions! (they change with each data structure)
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2) Direction from the equator
add 2 extra columns for the longitude and latitude They will contain : « 1 » if the latitude is North or the latitude is East « -1 » if the latitude is South or the longitude is West
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3) Calculation Add 2 extra columns that will contain the decimal coordinates for latitude and longitude
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3) Calculation Go to the formula field of Excel
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3) Calculation To calculate the decimal latitude you need to do the following operation: DecimalLat=(Degrees + Minutes/60 + Seconds/3600)* 1 if North or DecimalLat=(Degrees + Minutes/60 + Seconds/3600)* -1 is South
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3) Calculation select the end column and write the following formula in the formula batr by using cell references (e.g « B2 »: second columns second row, « F4 »: sixths columns fourth row)
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3) Calculation select the end column and write the following formula in the formula bar by using cell references (in the example =(E2+(F2/60)+(G2/3600))*H2)
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3) Calculation Repeat the same process for the longitude (by changing the references of the column)
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4) Generalisation Go to the first cell of the first row with decimal latitude and copy it (press CRTL +C at the same time)
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4) Generalisation Select immediately after the latitude in the latitude in the remaining rows. Keep the left-clik button pushed and move the mouse above them
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4) Generalisation Apply CTRL+V (keyboard) to apply the formula on the whole column, that will then be converted
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4) Generalisation Repeat the 2 last steps for the longitude
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5) Conclusion Your coordinates are now converted into decimal coordinates and ready to be exported into a GIS
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Important! The conversion doesn’t change:
the geographical reference system the accuracy of the data but it could change their apparent precision (4°20’ in DMS = in DD) So keep the original values in your database and doculent the reference system This is just a additional notation for the same values (to ease mathematical comparison on coordinates)
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