Sharing Tools and Final Thoughts

Sharing Tools
Last week and in a previous week, we shared tools that we created by adding the toolbox and the script to a zip file and sharing in this manner. This week we learned that this can be simplified into just one file by embedding the script into the script tool.  This is helpful when you want to share with the not so savvy user by reducing steps needed for using the script and for sharing with the they think they are savvy user and password protecting the script so that they can't get in there an fiddle with your code.  The script tool that we created included a prewritten script that only needed slight modification for embedding purposes.  The tool was used to select 6 parameters that selected a random number of points, within a certain distance of one another and created a buffer around each point.  These are my results.

Script tool dialog box and results

Final Thoughts

What is the most memorable, interesting or useful things I learned about using Python with ArcGIS during the course?  Hmm, let me think.  I learned that programming, in general, can be useful for repetitive, complex, lengthy tasks.  I have learned that I don’t think Python is as easy to learn as they say it is, and therefore doubt I will try to pick up any other additional programming languages.  But I have also learned that for every one person who gets and understands programming, there are thousands that benefit from it.  Where would any of us be without the programming pioneers of the early PC days?  We would probably still be hand drawing maps and shuffling through mounds of paper data trying to analyze it all.  Not everyone is cut out for everything, and that’s OK, it’s what makes this world work.  We each have our strengths and our weaknesses.  But when we identify our weakness and strive to make them strengths, that’s when we excel, that’s we step ahead of the next guy, that’s where we become a part of something bigger than us.  

To sum up this class, I have come to the realization that I do not have a programmer’s brain.  I have no idea how you guys remember all the things that go into modules and functions and command and syntax.  Maybe back in the day, when my brain hadn't lost quite so many cells, I would have had an easier time with this.  I hope one day maybe to retain just enough to keep me guessing on what I can do with Python. I definitely have a use for it at work.  Thanks for the instruction along the way.

Creating interdisciplinary collaboration through Python script tools

Landscape genetics is an area of research that combines population genetics, landscape ecology, and spatial analysis to understand the effects of landscape composition, configuration and matrix quality on gene flow and spatial genetic variation.  Knowledge of these areas typically requires more than one discipline of study so it makes sense that interdepartmental collaboration would be necessary.   The author, Thomas R. Etherington, identifies this area of concern, and using his knowledge of Python programming and ArcMap was able to create thirteen script tools for use by his colleagues that simplified basic, repetitive and complex processes.   Through use of script tools created and stored in an ArcMap toolbox, the author made it possible for non-GIS specialist to access the tools through a much simpler to understand GUI interface.  The author also recognizes that through script tools, geoprocessing and analysis can be combined for larger workflows.  While not specifically mentioned he is most likely referring to ModelBuilder.  Another point the author expands on is that since the scripts are created in Python, which is an open source language, they are easily accessible for other developers to use and modify to fit their own specific needs.

http://onlinelibrary.wiley.com/doi/10.1111/j.2041-210X.2010.00048.x/full

Python based GIS tools for landscape genetics: visualizing genetic relatedness and measuring landscape connectivity, Thomas R. Etherington, pages 52–55, Methods in Ecology and Evolution, January 2011, Volume 2, Issue 1

Creating Custom Tools

Say you have a script that you want to share with other users.  This script can be sent to another user and they can run the script.  But what if that script needs to have a variable parameter.  In a stand-alone script, the user would have to edit the script file and have some knowledge Python.  Wouldn't it be better to create a GUI tool that the end user could easily pull up in ArcMap and change those variables without having to know Python?  Creating a custom tool can do just that.  Many times users of ArcMap are not always well versed of the ins and outs of GIS, geoprocessing or Python programming.  A custom tool can be configured to choose specific parameters and perform functions detailed in the associated script.  A custom tool can be used in ModelBuilder to manipulate geoprocessing functions whereas a stand-alone script cannot. Additionally, print messages in a stand-alone script are only visible in an interactive window.  With a custom tool, print commands can be viewed in the Results window.

Our assignment this week was to create a custom tool based on a given script.  First we needed to create the toolbox and a script to it.  Then we associated a script file to the tool.  Parameters must be defined in the tool that correspond to the parameters in the associated script.  Once the parameters are established, clicking on the script tool will produce the following screen.

Script tool with established parameters

 A stand-alone script cannot run certain commands within a script tool.  For example, a simple print command such as print "Clipping", inname.name, must be modified to properly run in the script tool.  The arcpy.AddMessage function takes the place of the print command and commas are replaced with the plus symbol.  As you can see in the results below, printed messages can be viewed in the results window of a script tool.

Viewed messages in the Results window

Module 9: Debugging and Errors

Errors are an inevitable part of scripting.  It's not a matter of if they will happen, but when and where.  Knowing how to find the when and where is a vital part of scripting.  Syntax errors, exceptions, and logic errors are all possible types of errors. There are a number of ways to find where errors exists.  The PythonWin toolbar is a good place to start.  It can tell you if a an error occurred and on what line.  The debugger tool in PythonWin is also another useful tool in finding errors.  Being able to step through lines of code one at a time can pinpoint the location that a script stops working.  Commenting out lines of code and adding print statements are also helpful in finding errors.  Lastly, the try-except tool can be used to allow a script to run even if specific sections of code contain an error.

This weeks assignment was to locate script errors and correct them and to use the try-except command to show how a script can run even with an error present.

The first script contained two errors that needed to be found and fixed to display the names of the airports from module 6 data.

Script1_Results

The second script contained 8 errors that needed to be corrected.  I was able to locate the errors by using selective commenting and interpreting the interactive window results.

Script2_Results

The third script contained an error, but instead of fixing the error, we were to insert a try-except command that would allow the script to run even though there was an error in part A.

Script3_Results

Working with Rasters

Raster files are images that are used in ArcMap.  They can come from a variety of sources and formats including .img, .tif, and .jpg formats to name a few.  Python can be used to describe components of a raster file, to remap and reclassify landcover, and to calculate slope and aspect.  The most commonly used extension in working with raster files is the Spatial Analyst extension.  Within Python, the arcpy.sa module is most used and all functions should be imported.

Our lab this week had us use a number of arcpy.sa functions to remap and reclassify landcover as well as calculate a desired slope and aspect of the elevation raster file.  My final result can be seen in Results1.

Results1

I actually understood most of this lab.  Not sure why this week was so much more different than the previous weeks.  I still struggle with retaining the code and its proper usage, so I spend a lot of time looking for examples.  I would love to find a way to remember some of this stuff as it would be useful in my everyday work with ArcMap.  Not so much the spatial analyst, but definitely some of the other modules and functions we have seen up to this point.

Working with Geometries

Geometries can best be described as the bits and pieces that make up a feature.  This includes everything from a point or vertices that display the feature to the attribute data that contains the information on where those points should be placed.  Features such as polylines and polygons contain an array of point geometry.

This weeks lab we were to create a text file from an existing shp file.  A for loop with a .getPart() method was used to get all parts of the line feature class.  The second column of data shows each vertex point that was used to create the polyline for each river.

Mod7 Results

I'm not of fan of programming.  I find that it's the little mistakes that are sending me headlong into a brick wall every week.  But, for some reason, walking away from it for a day or two always seems to make things more clear.

Exploring and Manipulating Spatial Data

This week, we used Python to explore and manipulate data.  I still do not think I am getting the hand of for loops.  However, I did manage to create a half working script. These are the results of my script:

Results

I'm not entirely sure what I am doing wrong.  But, it's the 4th of July and I'm off to celebrate with some fireworks.  I hope you do too.