GIS

Related to Geographic Information Systems Technology. May include some Remote Sensing Information

ArcGIS and Vista

Lots of Windows users are looking forward to using Windows Vista (and some are already using it). Someday ArcGIS will be supported on Windows Vista ... but for now its not ! This ESRI Technical Paper explains more.

ArcGIS 9.2 Service Pack 2 (now available)

ArcGIS 9.2 SP 2 from ESRI is now available. There are separate downloads for ArcSDE 9.2 and ArcIMS 9.2.
A list of issues that are reportedly fixed by this service pack is available ... SP 2 issues fixed

Which NAD_1983_To_WGS_1984 to use ?

I often wonder which Geographic Transformation to use when going from NAD 1983 to WGS 1984 and when I'm faced with it I usually forget. Perhaps this blog post will be something I can refer back to when I need to. Apparrently after choosing one of the main three, it doesn't matter very much. The main three are _1 (for all of NA including Caribbean), _4 and, _5 for the lower 48. Perhaps its best to use 5 unless the area in question is outside the lower 48 (in which case you would use _1) as EPSG says that _5 supersedes _4.

Its so much easier to go from NAD 27 to NAD 83 as NADCON (the obvious choice for Americans) is just easier to remember !

See the ESRI Technical Article o

Single Use License (ArcView) and License Server (ArcInfo) on one computer

I recently discovered that it is possible to have a Single-Use License for ArcView 9.2 installed on a computer with a Concurrent-Use installation of ArcInfo 9.2. This allows users with a laptop to use the ArcView level of the ArcGIS software at home without the hassle of connecting to a license server through a VPN. Start with a complete installation of ArcGIS 9.2 and then proceed with these instructions.

1. At Run Prompt, type "regedit".
2. Go to HKEY_LOCAL_MACHINE -- SOFTWARE -- ESRI -- License.
3. Right-click inside the window on the right and go to New -- String Value.
4. Name the new Key "SingleUse_Installed" and make the value "Viewer". Close Registry Editor.
5. Open Desktop Administrator from Start -- All Programs -- ArcGIS -- Desktop Administrator

Story: GPS Devices Lead to Suspects' Home

Funny story about burglars of GPS equipment. Know what you are stealing !

GPS Devices Lead to Suspects' Home

Learning MapServer (UMN's Map Server cgi program)

I've been wanting to try the UMN's MapServer product. All the information about this great product is on the UMN MapServer website. Earlier this week I downloaded an installer for MapServer for Windows and installed it on my work computer. The installer is called ms4w and it installed everything I needed to get started with no problem including Apache, MapServer, GDAL, OGR. I downloaded the MapServer Demo application to look at.

Its been fun to work with and I hope to get something cool going eventually. For now my test application can be viewed at the very short list of

When Symmetrical Difference Is No Different

I don't understand why this doesn't work in ArcMap. Here are my inputs. both are in the same coordinate system (click to enlarge).

The input feature (the park buffer) is the violet colored area and the stewardship features are the tan colored areas. I'd expect the symmetrical difference to be the part of the violet-colored area that is visible underneath the stewardship areas.

Yet this is the result (which is the same as the buffer). This is very frustrating and I think it is a bug. I sure hope 9.2 works the way it should.

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.

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