topic Re: Distance between Points in Python Questions

Distance between Points

JoaoOliveira2 — Thu, 09 Oct 2014 20:40:59 GMT

here the thing-

in the same layer, I have POINT_X, POINT_Y and POINT_X_1, POINT_Y_1, as decimal degrees.

I´m trying to find the linear distance in meters from the 2 points.

I´m trying to get it with pyhton, using the below code, but I get always the same syntax error

000989 : Python syntax error: <value>

Any help appreciated

Thanks

Joao

pre-logic code

ef Haversine(Lat0, Lat1, Lon0, Lon1):

[INDENT]dlat = Lat0 - Lat1

dlon = Lon0 - Lon1

a = (math.sin(math.radians(dlat)/2 )*math.sin(math.radians(dlat)/2 )) + math.cos(math.radians(Lat1) )*math.cos(math.radians( Lat0 ) )*(math.sin(math.radians(dlon)/2 )*math.sin(math.radians(dlon)/2 ))

c = 2*math.atan2( math.sqrt(a ),math.sqrt(1-a ))

H = c * 6371

return H

[/INDENT]

Code:

Haversine( !POINT_Y! , !POINT_Y_1! , !POINT_X! , !POINT_X_1! )

Re: Distance between Points

SusanJones — Thu, 09 Oct 2014 20:59:56 GMT

At the moment this process is comparing apples and oranges and it will give incorrect results.

This said, the process needed is to build in a reproject function to take the coordinates from Geographic Coordinates (decimal degrees) into Map units (meters).

#Todo Get distance between 2 point

Step 1: Build up representation of 1st point in memory as PointGeometry Object

Step 2; Reproject point in map units

Step 3: Build up representation of 2nd point in memory as PointGeometryObject

Step 4: Reproject this into Map Units

Step 5: Compare the 2 points using Pythagoras Formula.

Attached is a function to perform the Reproject using the arcpy module

#projectSR

def projectSR (pt, sr): #sr = spatial reference, pt is geometry in memory

#constantts

gcs = arcpy.SpatialReference(2193) #2193 = factory code for NZ Transverse Mercator

gt = 'NZGD_2000_To_WGS_1984_1' #geographic transformation, if application

coords = []

ptgeom = arcpy.PointGeometry(pt, nztm).projectAs(gcs, gt)

coords.insert(0,(ptgeom.centroid.X))

coords.insert(1,(ptgeom.centroid.Y))

del ptgeom

return coords

Call projectSR to get the coordinates in map units meters and then you'll be able to use the Pythagoras theorem.

Susan

Re: Distance between Points

DanPatterson_Retired — Thu, 09 Oct 2014 22:07:26 GMT

If you still want to use Haversine, there are many examples on the web in python, for example