NameError: global name is not defined when performing task with FlowMapper in QGIS

Question

I'm using QGIS 2.8 and I'm trying to apply the FlowMapper plugin to create a visualization. I aim to follow the instructions in this blog post and this GIS.SE question, but something seem be going wrong.

The error is as follows:

2020-11-04T19:45:59 1 Traceback (most recent call last): File "/Applications/QGIS.app/Contents/MacOS/../Resources/python/plugins/FlowMapper/flowmapper.py", line 2655, in run SaveDirectory = SaveShpName NameError: global name 'SaveShpName' is not defined

I'm not sure what to do about this. So far, I've tried changing the input files by either switching to spaces instead of tabs between the data columns. That did not help though.

Added: Here are the files I've used. First, there is the locations of the cities:

Then there's the labels associated with them:

And finally, the incidence matrix:

All columns are separated by spaces. The paths to the respective files are:

/Users/maxmuller100/Documents/Data_Project/stud-steden-locaties.txt

and

/Users/maxmuller100/Documents/Data_Project/stud-steden-labels.txt

and

/Users/maxmuller100/Documents/Data_Project/stud-steden-matrix.txt

Answer 1

An error in line 2655 refers to this part of the code in flowmapper.py

#SaveDirectory = os.path.realpath(SaveShpName)
SaveDirectory = SaveShpName
flowpyv07.shapefilemaker(FlowType,CreateShpNodes,IncludeNodeNames,str(SaveDirectory), str(SaveShpName),str(SaveShpNameNodes),str(InputMatrixName),str(InputNodesName),str(InputNodeNamesName),str(combotext))

and it appears because SaveShpName was incorrectly initialized in flowpyv07.py via the function

def shapefilemaker(typeofcalculation,CreateShpNodes,IncludeNodeNames,fulldirectorystring,outputfilename,outputfilenamenodes,fulldirODinput,fulldirPTinput,fulldirPTNamesinput,combotext):

where some(or all) variables fulldirODinput,fulldirPTinput,fulldirPTNamesinput can not be created with a built-in function open(filename, 'r') probably due to issues in the input file content or a path to each of them.

So, there are several solutions I may suggest:

---

A short-time solution

I could get the desired flows in QGIS Wien 2.8.9, see image below.

When I opened your initial file "stud-steden-matrix.txt" in Notepad++ I see this

but when I open the same file in simple Windows's Notepad the result is different

So, all text files have to be formatted appropriately.

This is a FlowMapper's working window:

---

A long-time solution

1. I assume that the Plugin's developer (@cempro) will highly appreciate if you can assist with FlowMapper Plugin migration to QGIS 3.

2. Using a Virtual Layer, implementation was described in this article.

3. Setting a new workflow for QGIS 3 and putting as a possible solution here. For instance, I just implemented a workflow with native QGIS tools.

   1. Import a text file with points

   2. Generating all possible line connections between all points, you can use one of the possible approach described in this thread.

      For example, I used solution with a Virtual Layer with the following query

       select a.id || '_' || b.id as keyf, a.id as fromp, b.id as top, makeline(a.geometry, b.geometry) as geometry
       from "stud-steden-locaties" a, "stud-steden-locaties" b
       where a.id <> b.id
      

      Note: Here I created a special field with a.id || '_' || b.id this will play a key role in joining attributes from "stud-steden-matrix-list.csv"

      

   3. Drag&Drop "stud-steden-matrix-list.csv" into QGIS and apply a simple join between lines and .csv-file.

      

   4. Apply some visualization techniques to get flows, see image below

      

      It is possibly a complicated solution, so you may find a smarter one.

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References:

• Adjusting flow map styles in QGIS 2
• 'Global name not defined' concept in python
• FlowMapper Documentation