jchurchill's blog

My Approach to Geoprocessing with Python

I've done a bit of programming with ArcObjects in VB and VBA. I probably hadn't heard of Python until ArcGIS 9.0 came out. I've been interested in learning Python but never followed up on it because I can usually write it quicker in VBA (because I already know how to do it). I've been learning Perl over the past few months too so I understand how scripting languages can be very streamlined and effective for text manipulation and apparently for geoprocessing too. I recently watched a 60 minute tutorial on Scripting called “Getting Started with Scripting in ArcGIS 9”. Its worth watching to get an idea of how the syntax works but the take home is that its really quite easy and intuitive (they don't go into much detail). I think you'd still want a good reference book on hand to help you get started.

INT Grid Function can cause NoData Values

I took great care today to extract a section of 1" NED data using precise DD coordinates. To merge a large section of data together, I had to convert the data to integer data (the adf file was over the 2GB limit). I'd seen that before so I knew I had to convert to integer. I used the following syntax with the INT function to be sure the values rounded properly since INT simply rounds down ARC:newgrid = INT(oldgrid + .5). To my dismay, A whole section of the grid disappeared ! The problem appears to be some kind of overflow though I'm not sure how this data would store the kinds of values described. I used INT without the (+ .5) and the data was preserved.

The Article says:
Input to the INT function must be within the range of -2,147,483,583.0 to 2,147,483,583.0 (note: the range of createable floating point values is +/- 2,147,483,520.0). The output is all NODATA when the input exceeds this range.

Merge / Append doesn't work with GCS_Assumed_Geographic_1 (use ArcCatalog's Toolbox)

I've come across this before so I'm writing it down. The Merge tool in ArcToolbox 9.1 isn't letting me merge the Tiger shapefiles I got from the ESRI arcdata site. I think it may have to do with the assumed geographic coordinate system. However I changed it (for every shapefile) to GCS_North_American_1927 and still had some trouble with it. The Toolbox in ArcCatalog seems to work ok. I had several things going on in the ArcMap project prior to doing this but I changed the data frame to be the same as for the shapefiles. Oddly everything worked fine when I closed ArcMap entirely and ran Merge from the toolbox in ArcCatalog. I think they screwed this up somehow in 9.1. It used to work fine in 8.3.

Incidentally ... Somebody created the old geoprocessing wizard from 8.3 as an extension for 9.1. I used this extension before with some success.

PASDA

I attended the 7th Annual SW Pennsylvania Geo-Spatial Conference at California University Pennsylvania on Friday 8/25/2006. One session was devoted to PASDA which is a data warehouse for Pennsylvania that I'm familiar with. They have fast servers and are storing a lot of data (10's of TerraBytes) and their IMS tools for downloading are very cool. It sounds like they've spent a lot of effort improving navigation on the site through a wizard interface. I did a command line FTP to the site today to download all the 2004 NAIP imagery for the entire state. I didn't clock the download but It was seemingly very fast. I was very impressed with the described improvements to their site.

visit PASDA ... http://www.pasda.psu.edu/

SQL Tutorial

A gentle introduction to SQL. I saw this on Digg. Its a very simple tutorial on using SQL (at least everything I've done so far in the "tutorial" section is pretty simple). You actually run real queries yourself using your browser and an online database.

Follow this Link ... sqlzoo.net

Digg Generator (Put a live Digg Link on your website)

Odd that I'm posting this. I've never even posted a single story on Digg (though I've thought about it). This service is pretty cool because it actually allows the user to digg the story without ever leaving the site where the story is hosted.

The Story
The Digg Link
Digg Generator

Linux Command Line Tips

A nice collection of Linux Command Line Tips http://www.pixelbeat.org/cmdline.html. I believe that many of these translate into valid Unix commands as well. There are some advanced expressions here using regex and sed. I saw this on Digg recently.

So Now What ?

Here's what I've decided to do. Since I now have my own Drupal-powered blog, I will blog about family, fun, web etc on For All Intents & Purposes and blog here on For Many Intents & Purposes about GIS, computing, programming, web development etc. I think thats where my following is for this site anyway.

Drupal Site Debut

I'm proud to announce the debut of ...
For All Intents & Purposes II

It still needs a bit of configuration work but I got through the installation (which I thought was going to be the hard part). I may go through setting up a subdomain blog.jbchurchill.com and I'll have to learn how to manage multiple sites but this is pretty exciting for me and I can't wait to get it started. I'm not sure what will happen here with this site. Do I want to keep it going or try to transition into the new site ?!!?

Funny Error Messages

I dugg this one. Funny Errors from Windows Update, Nero, Remedy, Papa Johns Website, and Strange London Train System signs.

Funny Error Messages

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