I'm working on manipulating point coordinates into line segments. I have a series of GPS track points that I'm trying to get into individual links. Each line will only have a starting vertex and and ending vertex. I was successful in loading each point, starting with the second point, in copying the X,Y coordinates from the prior point. For example, point 2 has its GPS location in and X and Y column and it has the coordinate from point 1 in two other X and Y columns, point 3 has its X,Y values and the values from point 2. This has given me both the starting and ending coordinates.
I tried using the sample Python script from the help file, but it seems to skip segments. The only thing I can think is happening is that the X1 and Y1 and loading in as the same as X2 and Y2, so there is no line to be drawn, yet a feature is created. The other problem I've run into is that the vertices of the lines don't overlap the points.
mxd = arcpy.mapping.MapDocument("Current")# Define mxd to current file.
mapLyr1 = arcpy.mapping.ListLayers(mxd, "test_points") [0]
feature_info = list()
with arcpy.da.UpdateCursor(mapLyr1,["FID","Latitude", "Longitude", "E_Lat", "E_Long"]) as sCursor:
for row in sCursor:
if row[0] == 0:
lastLat = row[1]
lastLong = row[2]
else:
thisLat = row[1]
thisLong = row[2]
row[3] = lastLat
row[4] = lastLong
sCursor.updateRow(row)
Coords = [[thisLong, thisLat], [lastLong, lastLat]]#creates the X1, Y1 and X2, Y2 pairs
print Coords
feature_info.append(Coords)#append the X,Y pairs
lastLat = thisLat#turn current Y value into past Y value
lastLong = thisLong#turn current X value into past X value
#Loops through layer to create list of X,Y Pairs
with arcpy.da.SearchCursor(mapLyr1, ["Longitude", "Latitude", "E_Long", "E_Lat"]) as lineMaker:
for points in lineMaker:
p1, p2, p3, p4 = points[0], points[1], points[2], points[3]
pairs = [[p1, p2], [p3, p4]]
feature_info.append(pairs)
features = []
#Snippet from Help/ESRI Resources
for feature in feature_info:
# Create a Polyline object based on the array of points
# Append to the list of Polyline objects
features.append(
arcpy.Polyline(
arcpy.Array([arcpy.Point(*coords) for coords in feature])))
# Persist a copy of the Polyline objects using CopyFeatures
arcpy.CopyFeatures_management(features, "c:/temp/polylines.shp")I end up with the features looking like this:
I'm not sure if this is a scripting error alone, or if projections are playing a part too. If it were a projection issue, then all the lines would show up. I expect that if it were only a scripting error, all the points and lines would coincide.
Accepted Solutions
There were some issues with the script that I noticed when I actually run the code:
- Indexes to fields in row were from 1 to 4, should be 0 to 3
- the spatial reference in the polyline, was at the wrong location.
Just did a test based on a dbf table with the coordinates and this is the result:
Code:
import arcpy # location of input and output fc_in = r"C:\Forum\LineFromTbl\Coords.dbf" # or .dbf, or ? fc_out = r"C:\Forum\LineFromTbl\polylines1.shp" fld_lat_in = "Latitude" fld_lon_in = "Longitude" fld_lat_out = "E_Lat" fld_lon_out = "E_Long" flds = (fld_lat_in, fld_lon_in, fld_lat_out, fld_lon_out) # sr = arcpy.Describe(fc_in).spatialReference # if input is a featureclass, or: sr = arcpy.SpatialReference(4326) # where 4326 represents the WKID of the coordinate system features = [] cnt = 0 with arcpy.da.UpdateCursor(fc_in, flds) as curs: for row in curs: cnt += 1 if cnt == 1: lastLat = row[0] lastLong = row[1] else: thisLat = row[0] thisLong = row[1] row[2] = lastLat row[3] = lastLong curs.updateRow(row) features.append(arcpy.Polyline(arcpy.Array( [arcpy.Point(lastLong, lastLat), arcpy.Point(thisLong, thisLat)]), sr)) # provide sr lastLat = thisLat # turn current Y value into past Y value lastLong = thisLong # turn current X value into past X value del curs, row # Persist a copy of the Polyline objects using CopyFeatures arcpy.CopyFeatures_management(features, fc_out)
Hi Geoff,
First of all glad that you solved your problem. You should however take care when pasting the code to the thread. The indent are very important for the code to be valid. The code you posted and marked as the correct answer is not valid:
This should be:
etc...
You are using 3 loops for something that you can (and should) do in a single loop. If the the code I provided is generating an error, please provide a sample of the data and I will correct it. Just to be sure that the thread has a working code sample for other users that may have a similar problem.
