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Show different depths along line

ErinKennedy

Hello,

I am modeling some 3D underground pipe structures. Some of the pipes have quite deviant depths along the pipes (for example where they run under a canal). For these pipes, I have data with the xy locations of the lines and a seperate feature class of points that give the absolute depth. How can I put these lines in my model showing the correct depth along the line? Do I need to break up the lines where the points are to create a to and from height for each segment and how can I approach that efficiently? Or do you have a suggestion of an easier way to do this?

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XanderBakker

Hi Erin,

Have you tried creating a TIN from the 3D points and use the "Interpolate Shape (3D Analyst)" to assign the Z value to the polyline?

Kind regards,

Xander

ErinKennedy

Thanks for the response Xander.

Unfortunately, because the points are randomly distributed along where the lines run and not necessarily at the endpoints of the lines, the TIN it creates doesn't cover all the area that the lines do. So, my output after using interpolate shape makes it look like my lines are broken up and doesn't include some segments of the lines. Any further ideas on this?

XanderBakker

Hi Erin,

Is it possible to share a small part of your data? That makes it easier to see what can be done.

Kind regards,

Xander

ErinKennedy

Yes, thanks for the response. I put one of the lines and the related points in the zip file, as well as my created TIN and interpolation.

Pipetest.zip

XanderBakker

Hi Erin,

Thanks for posting the data. I see what you mean, the TIN will not cover the entire area needed by the line.

To solve this, I guess some programming would be needed. I started with something in Python, but the possibilities offered in ArcObjects for working with geometries is still superior (for instance snapping a point to the line and determining the M-position).

For how many lines would you like to do this? What do you want to do with the end points (should the slope be extrapolated towards the beginning and end based on the slope determined by the two points located nearest to these from and end points? Or should the last value (closest to from or to point) be used for these points?

I can look into this a little more, but it is going to take some time and the projects I'm working on currently don't give me much room for this.

Kind regards,

Xander

ErinKennedy

Thanks for the response Xander.

It is only a few lines in my study area that I have this issue with (7!), but my goal is to develop a method for conversion to 3D that can be applied to a greater area, which will probably have many more similar cases. So, I would like to find a way to automate the conversion as much as possible.

Unfortunately, I don't yet have any experience with python scripts (it is on my to-do list, but I am a busy student and GIS is only part of my study so it will probably have to be put off until I have some free time). So, for now I am thinking that I should add points at the ends of the lines where there are none and extrapolate the depths by hand. Then, create the TIN and interpolate the shape. But in my method I will note that this should be automated with a script if it were to be applied to a greater area.

Thanks for all the help!

ErinKennedy

After looking at the problem some more, I decided to use IDW (from the geostatistical analyst extension) to interpolate a raster from the points instead of creating a TIN, with an extent beyond the lines, then I used interpolate shape. This seemed to work okay and the results look good to me. But perhaps someone knows a reason why this isn't a good method?

XanderBakker

After looking at the problem some more, I decided to use IDW (from the geostatistical analyst extension) to interpolate a raster from the points instead of creating a TIN, with an extent beyond the lines, then I used interpolate shape. This seemed to work okay and the results look good to me. But perhaps someone knows a reason why this isn't a good method?

Hi Erin,

It is a good approximation, but keep in mind that IDW will not contain the actual value at the location where the points are known. It will smoothen the result, but maybe it's within your required precision.

Kind regards,

Xander

XanderBakker

Since I already started with some Python code I decided to give it a go and I came up with some crappy code that actually results in a single 3D line. So this only processes a single line and the points that are within a distance of 1m tolerance to that line. It works for a test set and also the data Erin attached to this thread.

It works like this:

it converts the vertices of the line to a list (X,Y,Z,M,"line"), Z = None and M is distance from start
the points are also converted to a list (X,Y,Z,M,"point"), Z has value and M is not set yet
the lists are merged together (M for points is calculated)
the first and last Z values are determined and set to the from and to points
the intermediate vertices are provided with a Z value based on the known values and M locations of points
the list is converted to a 3D polyline featureclass

import arcpy,math

fcPnt = r'C:\Project\_Forums\Erin\Pipetest\points.shp'
fcLine = r'C:\Project\_Forums\Erin\Pipetest\pipe.shp'
fcLine3D = r'C:\Project\_Forums\Erin\test.gdb\pipe3D' # output

tolerance = 1
fldZpnt = "abs_height" # "SHAPE@Z"

# fetch polyline
with arcpy.da.SearchCursor(fcLine, ("SHAPE@")) as cursor:
    for row in cursor:
        polyline = row[0]
del row

# get sr from input lines
sr = arcpy.Describe(fcLine).spatialReference

# put polyline crds in list
lstPnts1 = []
arr = arcpy.Array()
dist = 0
pnt = arcpy.Point(0,0)
for arr in polyline:
    for i in range(0,arr.count):
        prevPnt = arcpy.Point(pnt.X,pnt.Y)
        pnt = arr.next()

        # Add distance from startpoint (M)
        if i == 0:
            dist = 0
        else:
            dist += math.hypot(pnt.X-prevPnt.X,pnt.Y-prevPnt.Y)

        lstPnt = []
        lstPnt.extend((pnt.X,pnt.Y,pnt.Z,dist,"line"))
        lstPnts1.append(lstPnt)

##print "lstPnts1: {0}\n".format(lstPnts1)


lstPnts2 = []
cnt = 0
with arcpy.da.SearchCursor(fcPnt, ("SHAPE@X","SHAPE@Y",fldZpnt)) as cursor:
    for row in cursor:
        cnt += 1
        lstPnt = []
        lstPnt.extend((row[0],row[1],row[2],-1,"point"))
        lstPnts2.append(lstPnt)

del row
##print "lstPnts2: {0}\n".format(lstPnts2)

# merge lists together
lstPnts3 = []

# loop through segments of polyline
for i in range(1,len(lstPnts1)):
    X1,Y1,Z1,M1,geom1 = lstPnts1[i-1]
    X2,Y2,Z2,M2,geom2 = lstPnts1
    pnt1 = arcpy.Point(X1,Y1)
    pnt2 = arcpy.Point(X2,Y2)
    arrLine = arcpy.Array()
    arrLine.add(pnt1)
    arrLine.add(pnt2)
    line = arcpy.Polyline(arrLine)

    if i==1:
        lstPnts3.append(lstPnts1[i-1])

    for j in range(0,len(lstPnts2)):
        Xn,Yn,Zn,Mn,geomn = lstPnts2
        pntn = arcpy.Point(Xn,Yn)
        dist = line.distanceTo(pntn)
        if dist < tolerance:
            # determine M value, assume point is "on" line
            Mn = M1 + math.hypot(X1-Xn,Y1-Yn)
            lstPnt= []
            lstPnt.extend((Xn,Yn,Zn,Mn,geomn))
            lstPnts3.append(lstPnt)

    lstPnts3.append(lstPnts1)

##print ""
##print "X\tY\tZ\tM\tGeometry"
##for p in lstPnts3:
##    print "{0}\t{1}\t{2}\t{3}\t{4}".format(p[0],p[1],p[2],p[3],p[4]).replace('.',',')
##print ""

# no extrapolation, just propagate last know Z
firstZ = None
lastZ = None
cnt=-1
for p in lstPnts3:
    cnt+=1
    if p[2] != None:
        lastZ = p[2]
        if firstZ == None:
            firstZ = p[2]


##print ""
##print "first Z: {0}".format(firstZ)
##print "last  Z: {0}".format(lastZ)
##print ""

# update firstZ and lastZ for from and to point
lstPnts3[0][2] = firstZ
lstPnts3[len(lstPnts3)-1][2] = lastZ


##print ""
##print "X\tY\tZ\tM\tGeometry (lastZ en firstZ)"
##for p in lstPnts3:
##    print "{0}\t{1}\t{2}\t{3}\t{4}".format(p[0],p[1],p[2],p[3],p[4]).replace('.',',')
##print ""


# now fill up the blanks
print "Fill up the blanks"

cnt=-1
for p in lstPnts3:
    cnt+=1
    if p[2] == None:
        currM = p[3]

        # get known Z,M before current point
        for i in range(cnt-1,0,-1):
            if lstPnts3[2] != None:
                beforeM = lstPnts3[3]
                beforeZ = lstPnts3[2]
                break

        # get known Z,M after current point
        for i in range(cnt+1,len(lstPnts3),1):
            if lstPnts3[2] != None:
                afterM = lstPnts3[3]
                afterZ = lstPnts3[2]
                break

        if afterM - beforeM > 0:
            currZ = beforeZ + (afterZ - beforeZ) * (currM - beforeM) / (afterM - beforeM)
        else:
            # in case of 2 points on same location...
            currZ = beforeZ

        lstPnts3[cnt][2] = currZ

##print ""
##print "X\tY\tZ\tM\tGeometry"
##for p in lstPnts3:
##    print "{0}\t{1}\t{2}\t{3}\t{4}".format(p[0],p[1],p[2],p[3],p[4]).replace('.',',')
##print ""



# time to write the 3D line to a featureclass
features =[]
arr = arcpy.Array()
for p in lstPnts3:
    if p[4] == "line":
        pnt = arcpy.Point(p[0],p[1],p[2],p[3])
        pntg = arcpy.PointGeometry(pnt,sr,True,True)
        arr.add(pnt)

polyline3D = arcpy.Polyline(arr,sr,True,True)
features.append(polyline3D)

arcpy.CopyFeatures_management(features, fcLine3D)
print "ready..."

Maybe this is useful to someone...

Kind regards,

Xander

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