finding the centroid between two points

[janehansen]

Hi, I have a very large data set. Each row has a lat/long for a start point, and a lat/long for an end point. I am looking for the easiest way to locate the centroid between these two points and display them with out also showing the start and end point locations.

    Thanks,
    Jane

[MikeMacRae]

Hi, I have a very large data set. Each row has a lat/long for a start point, and a lat/long for an end point. I am looking for the easiest way to locate the centroid between these two points and display them with out also showing the start and end point locations.

    Thanks,
    Jane

Jane, is this a line dataset with a beginning point and ending point coordinates? You can add 2 new fields called "CENTROID_X and CENTROID_Y and then right click on the heading and 'Calculate Geometry' and in the first drop down, choose the associated centroid calculation (X Coordinate of Midpoint, Y Coordinate of Midpoint)

Mike

[janehansen]

Jane, is this a line dataset with a beginning point and ending point coordinates? You can add 2 new fields called "CENTROID_X and CENTROID_Y and then right click on the heading and 'Calculate Geometry' and in the first drop down, choose the associated centroid calculation (X Coordinate of Midpoint, Y Coordinate of Midpoint)

Mike

Hi Mike, no at this point it is an excel spreadsheet that contains the locational coordinates for both the start and end points for a specific event.  Once I import the data into arc map I will end up points only. One for the start point and one for the end point for each event/row in the table. I need to find the centroid for each of these events.

Jn

[MikeMacRae]

You could possible just do some math in python and program it to find the different between the x value of the start point and the x value of the end point and then divide by 2 and then do the same for the y values?

Something like (assuming you're using UTM coordinates)

start x = 39500
end x = 40500

difference is (40500 - 39500)/2 = 500 + 39500 = 40000 centroid x

Same for y

And then you can write that to your excel spreadsheet to 2 new fields (or in memory, depending on how you want to manage the centroid coordinate values) and then plot the centroid coordinates instead of the start and end coordinates.

Hope that points you in the right direction?

[MikeMacRae]

Sorry, i missed the part that you are working in Lat\Long. You could possibly calculate the lat\long to decimal degrees and then do the math on that and then convert back to lat long?

[janehansen]

Sorry, i missed the part that you are working in Lat\Long. You could possibly calculate the lat\long to decimal degrees and then do the math on that and then convert back to lat long?

Thanks Mike, so using decimal degrees I would use the same calculation as you did for UTM but using the decimal degrees?

[MikeMacRae]

Yes, I found a python function that you could probably use to do the conversion and then just do the math on the values it returns

http://stackoverflow.com/questions/2579535/how-to-convert-dd-to-dms-in-python

The stackoverflow site has tons of good python scripting examples.