Sunday, March 22, 2015

It's all part of the process (or subprocess as the case may be)

On occasion I make the case for installing python in order to extend the usefulness of the environment in Vr, or at least getting hold of some of the most useful standard libraries.  Well here is another good reason.  This is just a snippet that I will use later but I figure this is as good a place as any to keep track of it.

Before too long I want to write a script that will depend on running an external process, then interacting with the results of the process (no spoilers yet).  In order to do that I'm going to make something similar to the following call to process some files leaving the results in the working directory. The research I did here was to make sure I had a way to not proceed until the original process was complete.  Later I'll need to make sure I can run a shell command and capture the resulting output but this will do for now.

import subprocess
process = subprocess.Popen('lasboundary -i *rgb1.las -otxt')
print process.returncode
print '\a'
the last line is just to beep so I knew when it was done.

Wednesday, March 11, 2015

Reminder snippets - liblas and reading laz files

The other thing that I used to do with this blog is post things that I wanted to remember.  At one point the Vr forums were a good place to do this because it also gave an opportunity to share and collaborate.  Since that doesn't really seem to be happening any more I suppose I could drop things here and then come back to them later if necessary.  Yes I could just do this in a document but who knows maybe a new opportunity for some kind of sharing community will pop up again.

In this case I just want to remind myself that if Vr never adopts the .LAZ LiDAR compression format for reading, it would still be possible using liblas. This is simple a little interactive session that shows it is theoretically possible using my own data.

There may indeed be other better ways, but this seems to work fine.

>>> import liblas
>>> f=liblas.file.File(r'c:\tmp\N1915250.laz',mode='r')
>>> f

>>> p.classification
>>> p.x
>>> f.header.compressed
>>> f.filename

5 Minute Functions - 2

I haven't stopped coding, I've just stopped talking about it.  Again more a function of the fact that I doubt anybody really cares.  I noticed the other day that I have slightly over 300 python programs that have accumulated over the years.  Certainly there are the ones I am really proud of like the ones that translate a Vr file into a KML file or a TIN into  LandXML format because of the crucially useful functionality they add.  Then there are the ones I use multiple times an hour, like double points on a line, drive to points by user specified parameters, storing helpful window states, adding clamping points to DTM lines, and on it goes.  Lately I have noticed that I also just stop sometimes and write a quick program because as I mentioned in a previous post of a similar title, I can spend 5 minutes programming and save 15 minutes (and lots of wear and tear on the mouse clicking finger).  Not only is it worth it but it is also fun, keeps my brain lubricated, and gives me a base in case I find the task useful and want to come back later to add options, dialogs, or arguments that would make it more universal.

Here is an example, I have a few thousand points that got dumped into a file without regard to any distinction.  about 300 of them would be really helpful if they were in a certain layer and I don't want to miss any of them.  The only thing that makes them different is that there is a common string of text inside the feature code.  There may very well be an easy way to do this with Vr, but after a couple of tries I couldn't come up with a parameter that worked so I thought, "why not just write a quick script?".  In this instance I'll just hard code the search string and resulting changes. If I find it useful I may come back later and add a simple dialog to make it more agile.

print ' modified 6:23 AM 3/11/2015'
# Globally change something based on text in it's feature code
Copyright 2015 Dennis Shimer
No warranties as to safety or usability expressed or implied.
Free to use, copy, modify, distribute with author credit.

Simple beginning of a function to change entities based on their
feature code.

Variables of interest:
for EntNum in range ( Ws.GetSymCount(WsNum)):
    Sym.Load (WsNum, EntNum)
    if Sym.GetFc().lower().count(' fh'):
        print EntNum
print ('\a')

 It started out as about a half dozen lines in pyedi and doesn't amount to much more now. Nothing fancy, just something I can come back to if I need it again, and in this case it really helped.

I don't know, maybe I'll just start dumping more of these here. Doesn't hurt anything and though most of them aren't universally interesting it might give somebody an idea.

For anyone interested in trying VrPython for the first time or if you are early in the game, I suggest going to the earliest posts and working forward. I use VrPython every day for many wonderful things, needless to say it will change and could potentially damage a file. Any risk associated with using VrPython or any code or scripts mentioned here lies solely with the end user.

The "Personal VrPython page" in the link section will contain many code examples and an organized table of contents to this blog in a fairly un-attractive (for now) form.