ArcMap Field Calculator: Calculating Geometry using arcpy

One of the things I had not gotten around to doing in ArcGIS 10 was figure out how to directly manipulate the geometry of a record using the Field Calculator.  When I stumbled upon a bug in the way the Extract Values to Points tool handles Null geometries, I figured it was time to figure it out.  Setting the X, Y to 0,0 was sufficient for my needs.

I set the Parser to Python and the formula was simple once I figured out the syntax:

pPoint = arcpy.Point(0,0)

Then, to extend my knowledge, I wanted to see how to calculate the geometry based off of two fields (X and Y).   The only real trick is knowing the bracket field names using exclamation points instead of brackets:

arcpy.Point(!X!,!Y!)

So turns out everything it pretty easy and straight-forward.  Whew!

Walkthrough: Building custom UI elements using add-ins (ArcObjects .NET 10 SDK)

I was working my way through this ESRI Walkthrough: Building custom UI elements using add-ins (ArcObjects .NET 10 SDK).  And came across a couple minor errors that I had to correct during the process.

First, while implementing the OnClick() code for ZoomToLayer.vb, Visual Studio gave me a “Name ‘ArcMap’ is not declared.” error.

In the walk-through, they mention that the ArcMap method of your class.  For me, however, it appeared under the .My method.  Not sure if this is something specific to my set-up or, as I’m guessing, something that got changed after the first documentation was created and the final libraries published.

The fix is just adding  “My.” to the namespace in this line:

ZoomToActiveLayerInTOC(TryCast(ArcMap.Application.Document, IMxDocument))

To get this:

ZoomToActiveLayerInTOC(TryCast(My.ArcMap.Application.Document, IMxDocument))

When I added the code for AddGraphics.vb, I got 8 errors.  There was essentially two errors, repeated four times.  I took a screen shot after fixing the first error pair:

The fixes in this case was also to use the complete name space path.  Examples:

Change this:

If (geometry.GeometryType) = esriGeometryType.esriGeometryPoint Then

To this:

If (geometry.GeometryType) = ESRI.ArcGIS.Geometry.esriGeometryType.esriGeometryPoint Then)

And change this:

simpleMarkerSymbol.Style = esriSimpleMarkerStyle.esriSMSCircle

To this:

simpleMarkerSymbol.Style = ESRI.ArcGIS.Display.esriSimpleMarkerStyle.esriSMSCircle

Overall, the walk-through is very well done, just a couple minor tweaks.  I am now working my way through modifying an existing solution–one that included seven projects–to see if I can create an ArcGIS 10 Add-In.

ArcBruTile

Stumbled across ArcBruTile, an ArcMap application that allows you to display map tile services–such as OpenStreetMap, Google Maps, Bing, Spatial Cloud, and Tile Map Service (TMS)–in your ArcMap documents.   It works pretty well from my preliminary testing of it.   I have found that at times that the graphical tiles are distorted but I am guessing it is because they are optimized for display in a specific projection, at specific scales and, in ArcMap, you can use any projection/scale combination you want.

This is a free, open-source project that is still in Beta but definitely an application I plan to keep an eye on.  As with any open-source project, the cool thing is the code is available for you to look at, learn from, and hopefully contribute to.

Create Geologic Cross Sections–eXacto Section v. 2.0, ArcMap 9.3

The Create Geologic Cross Sections–eXacto Section v. 2.0, ArcMap 9.3 written by Jennifer Carrell of the Illinois State Geological Survey is a handy tool for creating cross sections.

It requires ArcGIS and a 3D Analyst Extension license.

You can create profiles against multiple DEMs at once, define the vertical exaggeration, and have it include contact points.  It is well documented and comes with sample data to use with the tutorial.

I did not see it mentioned but it also include a personal geodatabase that include a grid that can be used along with the profiles you create.

If  you make profiles, think this is definitely an option you should look at.  The fact that it is a VBA application is a bit worrisome in that its lifespan is limited.

Michigan Office of Geological Survey

The Michigan Office of Geological Survey appears to have pdf versions of all the documents in their Digital Geological Library available for download.  The transcripts of some early (beginning in 1871) field notes are a fun inclusion in the available archives.

Actual GIS data was a bit hard to find although I found both bedrock geology and quarternary geology available from the state Geographic Data Library in shapefile format.  I also found oil and gas well data but did not download it.

The data carried minimal attribution, one interesting thing I found in the bedrock data was the red, green, blue values apparently used for each polygon.

One thing to be aware of is that the shapefiles do not come with a prj file which could be a problem.  Michigan has their own defined coordinate system called Michigan GeoRef.  This coordinate system defines the entire state into a single zone instead of multiple zones like the USGS’ stateplane system does.  This is nice to work with UNLESS it comes undocumented as I found out while doing some consulting work in Au Train, Michigan a decade ago–I was able to finally find something online about it around 2 am one morning but I think I still have scars from the head-pounding that occurred that night.

ESRI, however, makes it easy to deal with this data–they include the specifications for Michigan GeoRef in inventory of predefined coordinate systems that ships with ArcGIS.  If you define the projection on each shapefile, it will then load automatically in real-world coordinates.  To define the projection on a shapefile, right-click on it in ArcCatalog and select “Properties…”.  Select “XY Coordinate System” on the Shapefile Properties dialog.  Hit the “Select” button and navigate to Projected Coordinate Systems-State Sytems-NAD 1983 Michigan GeoRef (Meters).prj.  Hit the “Add” button and then the “Apply” button.  Repeat for any other shapefiles you download.

One item I found out about ArcGIS while doing this is that if you change the projection on a shapefile, it will recognize that change the next time you use that data.  I originally set the units to be feet on the data so it did not load in the proper real-world location.  I saved my ArcMap document, quit out, and corrected the problem.  When I re-opened the document, Michigan had migrated back to where we are used to seeing it.  This contrasts with how ArcView 3.x use to handle raster data, you had to actually remove the layer from your view and re-load it to recognize the change in spatial references.

Sticky Move Tolerance

While I am pretty experienced in editing data in previous generations of ESRI’s software, I have not done a lot in ArcGIS. So in my new position where I am supporting a group of geologists who do a lot of data creation in ArcMap, I am learning some of the intricacies of the ArcGIS platform.

One of the potential gotchas that a coworker informed me about that I was vaguely aware of was the issue of sticky move tolerances. What can happen, when editing existing features, is that each time you select a feature it can easily get moved very slightly if the mouse moves while the feature is selected. While the movement itself may be well within any allowable accuracy requirements, it can make a huge mess if you are working with a shapefile polygon coverage for example.

ArcMap has a setting, Sticky Move Tolerance, that helps prevent these tiny, accidental moving of features.  A feature will not be moved until the mouse moves at least as many screen pixels as this setting.  The default setting is 0, disabling this feature.

This setting can be set changed under Options on the Editor Toolbar.

The Sticky move tolerance is on the General tab.  In this example, I have my setting at 25 pixels which may be a bit high but I do not do a lot of data editing myself so it is workable.  The downside of having it set this high is if I want to move a feature just a tiny bit, I have to first drag the mouse relatively far away and then bring it tighter into where the feature is.

Not sure how well this is documented although it can be found in the help system.

http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=Moving_features

ArcMap-Excel Join Error

Came across a new ArcMap bug today. A staff member was trying to join an Excel 2007 file (.xlsx) to a point shapefile in ArcMap and it did not appear to be working. She only had Office 2003 on her machine so I tried it on my spanking new machine that has 2007 installed. Same result–the fields get appended but they are all blank.

I discovered, however, that when I had the table open, if I switched form showing ALL records to only the selected, Poof!!! The values filled in. From there I was able to successfully export the data to a new shapefile that always showed the values.

I have an inkling that the file name, which contained space and other special characters, may have been a factor.

August 11, 2010 Addendum:

I was just working with some more and, after joining a table to an Excel table, having all the fields look blank, I discovered that if I close and then re-open the table all looks good–all fields have values.

Another problem I had is that even after successfully joining a table to the Excel table and creating an XY Event Theme from it, I was unsuccessful in exporting it to either a shapefile or a personal geodatabase feature class.  My personal opinion at this point would be to convert the Excel file to a different format before working with it in ArcGIS.