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How is the LRS ArcGIS Measure Along a Line implemented?

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I'm trying to replicate a nasty corner case in a LRS implementation that doesn't agree with ArcMAP measure tool. I've tried measuring distance in its native shp coordinate system NAD83 (27916) to no avail. (basically same results)

My question is how are the distances calculated along a line for the LRS system. My current distance function (for 4326) is the following.

EARTHRADIUS = 3963.190592 # miles



'''

used in distance

'''

def deg2rad(d):

    return d * math.pi / 180.0



# in miles

def distance(pt1, pt2):

    dLat = deg2rad(pt2[1] - pt1[1])

    dLng = abs(deg2rad(pt2[0] - pt1[0]))

    dLat2Sin = math.sin(dLat / 2)

    dLng2Sin = math.sin(dLng / 2)

    a = dLat2Sin*dLat2Sin + math.cos(deg2rad(pt1[1]))*math.cos(deg2rad(pt2[1]))*dLng2Sin*dLng2Sin

    return 2.0 * EARTHRADIUS * math.atan2(math.sqrt(a), math.sqrt(1-a))

For most geometries the distance between the ESRI LRS and mine are nominal but this one has something different. I've dealt with larger linestrings before (30+ miles) with no issues. Previously these other larger linestrings have worked fine throughout the alignment, however with this edge case I'm getting ~.5 miles difference (my implementation distances are always larger) between the two implementations by the end.

Is distance calculated a different way via the LRS implementation, is my geometry duplicating previous points possibly, or is it possible coordinate system error is actually sneaking in?

arcmap line distance linear-referencing

share|improve this question

asked 13 mins ago

Charles MurphyCharles Murphy

1

New contributor

Charles Murphy is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

add a comment | 

0

I'm trying to replicate a nasty corner case in a LRS implementation that doesn't agree with ArcMAP measure tool. I've tried measuring distance in its native shp coordinate system NAD83 (27916) to no avail. (basically same results)

My question is how are the distances calculated along a line for the LRS system. My current distance function (for 4326) is the following.

EARTHRADIUS = 3963.190592 # miles



'''

used in distance

'''

def deg2rad(d):

    return d * math.pi / 180.0



# in miles

def distance(pt1, pt2):

    dLat = deg2rad(pt2[1] - pt1[1])

    dLng = abs(deg2rad(pt2[0] - pt1[0]))

    dLat2Sin = math.sin(dLat / 2)

    dLng2Sin = math.sin(dLng / 2)

    a = dLat2Sin*dLat2Sin + math.cos(deg2rad(pt1[1]))*math.cos(deg2rad(pt2[1]))*dLng2Sin*dLng2Sin

    return 2.0 * EARTHRADIUS * math.atan2(math.sqrt(a), math.sqrt(1-a))

For most geometries the distance between the ESRI LRS and mine are nominal but this one has something different. I've dealt with larger linestrings before (30+ miles) with no issues. Previously these other larger linestrings have worked fine throughout the alignment, however with this edge case I'm getting ~.5 miles difference (my implementation distances are always larger) between the two implementations by the end.

Is distance calculated a different way via the LRS implementation, is my geometry duplicating previous points possibly, or is it possible coordinate system error is actually sneaking in?

arcmap line distance linear-referencing

share|improve this question

asked 13 mins ago

Charles MurphyCharles Murphy

1

New contributor

Charles Murphy is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

add a comment | 

I'm trying to replicate a nasty corner case in a LRS implementation that doesn't agree with ArcMAP measure tool. I've tried measuring distance in its native shp coordinate system NAD83 (27916) to no avail. (basically same results)

My question is how are the distances calculated along a line for the LRS system. My current distance function (for 4326) is the following.

EARTHRADIUS = 3963.190592 # miles



'''

used in distance

'''

def deg2rad(d):

    return d * math.pi / 180.0



# in miles

def distance(pt1, pt2):

    dLat = deg2rad(pt2[1] - pt1[1])

    dLng = abs(deg2rad(pt2[0] - pt1[0]))

    dLat2Sin = math.sin(dLat / 2)

    dLng2Sin = math.sin(dLng / 2)

    a = dLat2Sin*dLat2Sin + math.cos(deg2rad(pt1[1]))*math.cos(deg2rad(pt2[1]))*dLng2Sin*dLng2Sin

    return 2.0 * EARTHRADIUS * math.atan2(math.sqrt(a), math.sqrt(1-a))

For most geometries the distance between the ESRI LRS and mine are nominal but this one has something different. I've dealt with larger linestrings before (30+ miles) with no issues. Previously these other larger linestrings have worked fine throughout the alignment, however with this edge case I'm getting ~.5 miles difference (my implementation distances are always larger) between the two implementations by the end.

Is distance calculated a different way via the LRS implementation, is my geometry duplicating previous points possibly, or is it possible coordinate system error is actually sneaking in?

arcmap line distance linear-referencing

share|improve this question

asked 13 mins ago

Charles MurphyCharles Murphy

1

New contributor

Charles Murphy is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

EARTHRADIUS = 3963.190592 # miles



'''

used in distance

'''

def deg2rad(d):

    return d * math.pi / 180.0



# in miles

def distance(pt1, pt2):

    dLat = deg2rad(pt2[1] - pt1[1])

    dLng = abs(deg2rad(pt2[0] - pt1[0]))

    dLat2Sin = math.sin(dLat / 2)

    dLng2Sin = math.sin(dLng / 2)

    a = dLat2Sin*dLat2Sin + math.cos(deg2rad(pt1[1]))*math.cos(deg2rad(pt2[1]))*dLng2Sin*dLng2Sin

    return 2.0 * EARTHRADIUS * math.atan2(math.sqrt(a), math.sqrt(1-a))

share|improve this question

asked 13 mins ago

Charles MurphyCharles Murphy

1

New contributor

Charles Murphy is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

asked 13 mins ago

Charles MurphyCharles Murphy

1

New contributor

Charles Murphy is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 13 mins ago

Charles MurphyCharles Murphy

1

New contributor

Charles Murphy is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 13 mins ago

Charles MurphyCharles Murphy

1