topic Re: da Insert cursor writing empy geometry in Python Questions

da Insert cursor writing empy geometry

ZacharyHart — Tue, 27 Sep 2016 19:03:30 GMT

I'll preface this by saying I'm pretty weak on cursors but trying to boot camp myself to basic proficiency.

I'm trying to create a simple script that will take a point feature class and create lines from them. These points are the start point of the the line and for sake of demonstration here, the endpoints are defined mathematically from them. Simple 2-point lines.

startingPt = "STARTING_POINTS" #point feature layer in MXD
fields = ['SHAPE@X', 'SHAPE@Y']

point = arcpy.Point()
array = arcpy.Array()

featureList = []
insert = arcpy.da.InsertCursor(r"D:\Temp\Lines.shp",['SHAPE@'])

with arcpy.da.SearchCursor(startingPt, fields) as cursor:

    for row in cursor:
       startX = row[0]
       startY = row[1]
       array.add(point)
       endX = startX + 660
       endY = startY + 660
       array.add(point)
       polyline = arcpy.Polyline(array)
       insert = arcpy.da.InsertCursor(r"D:\Temp\Lines.shp",['SHAPE@'])
       insert.insertRow([polyline])

       print "Start: {},{} End: {},{}".format(startX,startY,endX,endY)
del cursor

The script successfully writes rows to the target, but the geometry is empty. I'm sure there is a simple (and stupid) mistake in the code. Any help is appreciated and I'm totally open to suggestions. I'd rather not have a copy features or append operation but just an insert unless my logic is totally flawed here.

Thanks!

Re: da Insert cursor writing empy geometry

VikramS — Tue, 27 Sep 2016 19:20:42 GMT

Hello,

In your code you forgot to build the point . Hopefully that should fix your issue

for row in cursor:
startX = row[0]
startY = row[1]

point = arcpy.Point(startX , startY)
       array.add(point)
       endX = startX + 660
       endY = startY + 660
       array.add(point)
       polyline = arcpy.Polyline(array)
       insert = arcpy.da.InsertCursor(r"D:\Temp\Lines.shp",['SHAPE@'])
       insert.insertRow([polyline])

Re: da Insert cursor writing empy geometry

DanPatterson_Retired — Sat, 11 Dec 2021 19:13:37 GMT

plus

point = arcpy.Point(endX , endY)
array.add(point)‍‍

otherwise the venture is pointless

Re: da Insert cursor writing empy geometry

ZacharyHart — Tue, 27 Sep 2016 19:45:41 GMT

Thanks! I just stumbled across another post wherein which someone was recalling words from you Dan Patterson‌ about setting the spatial reference...tried that and it wasn't the issue. I cleaned up the code a bit. Again, I'm totally up to suggestions, but this works!

startingPt = "STARTING_POINTS" #point feature layer in MXD
fields = ['SHAPE@X', 'SHAPE@Y']

#point = arcpy.Point()
array = arcpy.Array()
sr = arcpy.Describe(startingPt).spatialReference

insert = arcpy.da.InsertCursor(r"D:\Temp\Lines.shp",['SHAPE@'])

with arcpy.da.SearchCursor(startingPt, fields) as cursor:

    for row in cursor:
       startX = row[0]
       startY = row[1]
       endX = startX + 660
       endY = startY + 660

       array.add(arcpy.Point(startX, startY))
       array.add(arcpy.Point(endX, endY))

       insert = arcpy.da.InsertCursor(r"D:\Temp\Lines.shp",['SHAPE@'])
       polyline = arcpy.Polyline(array,sr)
       insert.insertRow([polyline])
       array.removeAll()

       print "Start: {},{} End: {},{}".format(startX,startY,endX,endY)

del cursor

Re: da Insert cursor writing empy geometry

DanPatterson_Retired — Tue, 27 Sep 2016 19:54:41 GMT

Looks like that should work, now that you have both the start and end points added to the array, you have enough points to form a 1D line, because it is possible to form a line with 1 point if you aren't careful. The spatial reference is also critical since you will get geometry inaccuracies if not use.

For commentary,

bullet-proof your code for python 3.x by changing all print statements to print functions ie. print(stuff goes in here)
although permissable, I would suggest collecting all your geometries that you want to create, then open up a new insertcursor outside of the searchcursor and create your geometries as you go along.

Otherwisey you are good-to-go

Re: da Insert cursor writing empy geometry

ZacharyHart — Tue, 27 Sep 2016 20:12:28 GMT

Dan_Patterson‌ Thanks so much for the suggestions! I'm currently in the process of adding rotation to each line with some basic trig. Regarding your suggestions:

I implemented this; was totally unaware of this. Thanks!
Are you suggesting I un-nest the two cursors? Again, I'm a real hack here, so if you had an example or reference that would be great. Any harsh words/warnings regarding poor practice of the structure of cursors as they are now?

Re: da Insert cursor writing empy geometry

DanPatterson_Retired — Tue, 27 Sep 2016 20:48:27 GMT

no examples off hand, but Darren Wiens‌ does a lot of cursor work so probably has some examples on hand.

The only reason I suggest, is that you can produce functions (ie def blah( .... ) ) that may do basic search cursor work collecting shapes (for instance) and then a separate insertcursor that does the writing to a new file.

As for geometry, /blogs/dan_patterson/2016/09/01/distance-calculations-using-the-field-calculator has some field calculator expressions that can be stripped to get azimuth of 2 point polylines. simply degrees(arctan2(dy,dx)) in pseudocode where dy is difference in y . Do not use for data in decimal degrees, it is a whole different equation.

Re: da Insert cursor writing empy geometry

DarrenWiens2 — Tue, 27 Sep 2016 21:50:07 GMT

You've got two identical lines that create an insert cursor. You only need to create it once - the line before you've created the search cursor. So, you may as well delete the line that re-creates the insert cursor within the search cursor.

As far as I'm concerned, it's ok to nest an insert cursor within a search or update cursor. I don't know the inner workings, but insert cursors (which run only when called) are quite different from search and update cursors (which loop through all features or those that meet the where clause criteria). You can run into trouble nesting any combination of search or update cursors, especially with large datasets, because it compounds the looping.

Re: da Insert cursor writing empy geometry

ZacharyHart — Wed, 28 Sep 2016 12:25:26 GMT

Dan, thanks for the insight and what a treasure trove in the article you wrote! Thanks!

Re: da Insert cursor writing empy geometry

ZacharyHart — Wed, 28 Sep 2016 12:28:37 GMT

Darren,

thanks for picking up on my bonehead move there! Thanks for the additional insight regarding the cursors. Much appreciated!

Re: da Insert cursor writing empy geometry

ZacharyHart — Wed, 28 Sep 2016 15:15:48 GMT

Darren Wiens‌ Dan Patterson‌

I broke it. No errors. Output FC is getting created but nothing is getting inserted. Previously I was just using an existing FC I made for sake of demonstration. Now I'm want to have the script create the FC. I've also tried using the old temp shape as a template and still not inserting. FWIW, shouldn't be anything to do with the rotation...the coordinates print right etc and I had this working up until I tried to have the cursor insert to a newly created FC.

If I explicitly set the existing output shapefile in the insert cursor like:

#Open Insert Cursor
insert = arcpy.da.InsertCursor(r"D:\Temp\Lines.shp",['SHAPE@'])

Then it works.

The current code below fails to write/insert any rows to the target FC. I've also tried to have the input points and output lines exist in different GDBs as a test; this didn't resolve the issue. Curiously, often when trying to open the empty output line FC, ArcMap crashes.

import arcpy, os, sys, math
from itertools import cycle
#Environment settings
arcpy.env.overwriteOutput = True
outGDB = arcpy.env.scratchGDB
#Local Variables
#startingPt = arcpy.GetParameterAsText(0)
#rotation = int(arcpy.GetParameterAsText(1))
#dist = int(arcpy.GetParameterAsText(2))
startingPt = "STARTING_POINTS"
dist = 660
angles = [0,90,180,270]
rotation = cycle(angles)
outName = "crz_lines"
#Create target polyline FC
sr = arcpy.Describe(startingPt).spatialReference
outLine = arcpy.CreateFeatureclass_management(outGDB,outName,"POLYLINE","","","",sr)
#Create an array object
array = arcpy.Array()
#Open Insert Cursor
insert = arcpy.da.InsertCursor(outLine,['SHAPE@'])
fields = ['SHAPE@X', 'SHAPE@Y']
with arcpy.da.SearchCursor(startingPt, fields) as cursor:

    for row in cursor:
       #Set Start points
       startX = row[0]
       startY = row[1]
       #Convert rotation values in list from degrees to radians
       rad = math.radians(next(rotation))
       #Calculate endpoints
       endX= startX + (math.cos(rad) * dist)
       endY= startY + (math.sin(rad) * dist)
       #Add points to array
       array.add(arcpy.Point(startX, startY))
       array.add(arcpy.Point(endX, endY))
       #Create Polyine object based on the array of points
       polyline = arcpy.Polyline(array,sr)
       #Insert the feature
       insert.insertRow([polyline])
       array.removeAll()
       print ("Start: {},{} End: {},{}".format(startX,startY,endX,endY))
del cursor

Re: da Insert cursor writing empy geometry

NeilAyres — Wed, 28 Sep 2016 15:48:55 GMT

delete the insert at the end as well.

Re: da Insert cursor writing empy geometry

NeilAyres — Wed, 28 Sep 2016 15:49:52 GMT

Otherwise the cursor is still open and the insert haven't yet been written or committed.

Re: da Insert cursor writing empy geometry

ZacharyHart — Wed, 28 Sep 2016 15:54:15 GMT

Hi Neil, thanks for the response. That doesn't seem to be the issue.

To be clear, if i explicitly set the insert cursor to the existing shapefile, the features are written as expected. If I use the newly created FC in the fGDB, then nothing is written (not even empty geometry).

Re: da Insert cursor writing empy geometry

NeilAyres — Wed, 28 Sep 2016 15:58:36 GMT

Humour me, create a specific fgdb in a location on disk "C:\Temp\MyData.gdb" or something.

Point the create features at that. Make sure you set the environment.workspace variable correctly.

I can't see from your original code where the input points are coming from.

Re: da Insert cursor writing empy geometry

ZacharyHart — Wed, 28 Sep 2016 17:02:41 GMT

Neil Ayres‌

Neil you're on to something here. Here are my application level (arcgis desktop) environments:

Creating an fGDB as recommended and using

outGDB = r"D:\TEMP\test.gdb"

Writes the output as expected.

As mentioned earlier, I also tried to have the input points located (default.gdb) separate from the target lines (scratch.gdb) but that didn't work. Perhaps I have to explicitly set my workspace in the script.

I'm not understanding why I can't write to the scratchGDB.

If you or anyone suggests I start a new post instead, I'll be glad to.

UPDATE:

when I run this as a script tool the cursor inserts to the FC in the scratch GDB as expected.

Re: da Insert cursor writing empy geometry

DanPatterson_Retired — Wed, 28 Sep 2016 22:26:24 GMT

dont work in that 'Users' space. That area gets bloated... trust me... we ban our students from that area completely

Re: da Insert cursor writing empy geometry

ZacharyHart — Thu, 29 Sep 2016 11:45:02 GMT

Dan,

I'll heed that advice. I've become used to relying upon the scratchGDB because the script readily translates into the published environment on our AGS.

I'm still at a loss why it worked as a script tool, but not in the Python console. Oh well! Thanks for everyone's help!