Posts Tagged ‘geometry’

Problems Dissolving in ArcMap, Try Repairing Geometry First

Tuesday, July 14th, 2009

[Editor’s note: I was having trouble last week dissolving a shapefile based on a common attribute. I kept getting the following error: “Invalid Topology [INCOMPLETE_VOID_POLY]“. Not entirely helpful! A little Google searching turned up the following tip from ESRI.]

Republished from ESRI.

Problem:  Some Overlay Tools, such as Intersect, return unexpected results or fail

Description

Results do not look correct or operations fail with strange errors such as:

“Invalid Topology [INCOMPLETE_VOID_POLY]“.

If this type of error has occurred, it is most likely to occur when using one of the following:
Clip, Erase, Identity, Intersect, Symmetrical Difference, Union, Update, Split Featureclass to Coverage, Dissolve, Feature to Line, Feature To Polygon, Integrate, or ValidateTopology.

Cause

It is possible that tool outputs may be strange or incorrect because one or more features in the input feature class have geometry problems. Some examples of geometry problems are:

· short segments
· null geometry
· incorrect ring ordering
· incorrect segment orientation
· unclosed rings
· self-intersections or empty parts

Solution or Workaround

If such errors occur or the output looks incorrect, the first step in assessing the situation is to run the ArcToolbox tool Data Management Tools > Features > Check Geometry. -show me

[O-Image] Check Geometry

This tool provides a list of the invalid features in the feature class and a short description of the problem. Features with problems can be fixed in one of two ways:

  • Editing the feature class with the geometry problem, and fixing each individual problem identified. Some of these problems, like non-simple geometry, can be fixed by double-clicking the feature in the editor and saving the edits.
  • Running the ArcToolBox tool Data Management Tools > Features > Repair Geometry on the feature class containing the problem features. -show me

Molecular Frameworks, the Building Blocks of All Life (Wired mag)

Monday, March 9th, 2009

[Editor's note: Blast from your chemistry class, Wired profiles the 30 most common molecular shapes, nature's "shape alphabet".]

Republished from Wired magazine.
By Erin Biba Email 02.23.09

Sure, the world is complicated, but not as complicated as you might think. It turns out that most organic molecules—the kind of chemicals that make food tasty, perfumes fragrant, and life alive—derive from a few relatively simple architectures.

Together with a bunch of data-minded colleagues, Alan Lipkus of the Chemical Abstracts Service took a deep dive into his organization’s century-old library of 24 million organic compounds—most of them synthetic. They found that more than half are built from just 143 basic shapes, or “frameworks.” And the rest? Well, building those requires the other 836,565 cataloged frameworks.

Why do a handful of fundamental shapes get all the work? In part because chemists typically create new molecules—in the search, say, for potential new drugs—from the ones they’re familiar with. It’s cheaper. But Lipkus hopes that showcasing this lopsided approach will encourage researchers to work farther out on the long tail of molecular geometry. “A lot of structures have not been fully explored,” he says. “There could be interesting things to discover.” Here’s a snapshot of the newly discovered shape-alphabet.

Top 30 Molecular Shapes

Molecules are clusters of atoms joined like Tinkertoys. The range of possible structures is vast, but they can all be categorized by “molecular framework”—the underlying rings and connectors. Most common by far is the hexagon—a ring of six atoms, with one at each corner, that’s the basis for nearly 10 percent of known organic compounds. Here are the top 30 most common frameworks, with frequency of occurrence in parentheses.

Continue reading a Wired . . .