Posted by & filed under GIS, Technology.

According to the ESRI Shapefile Documentation,
“The neighborhood to the right of an observer walking along the ring in
vertex order is the inside of the polygon”.  Meaning that all normal or
“clean” polygons are drawn in a clockwise fashion.  When it comes to
holes in the polygons, these are defined by a counterclockwise path
delineating the polygon.
The first step to
determining if a polygon is an additive vector or a subtractive one is
to determine the direction in which the polygon is formed.  ESRI
Shapefiles do not support polygons that cross their own lines, which
makes calculating data with them a bit easier.  One method to determine
the direction the polygon is formed is by using Green’s Theorem.
This method would require one to take the current coordinate (x1,y1),
and the next one (x2,y2), and apply the following formula:
∑(x2-x1)*(y2+y1).  For each line segment, one would then need to add
the result to a running total, and if the number ends up being
positive, the polygon is clockwise, and if it is negative, the polygon
is counterclockwise.
The Formula:

Example:

KML code:

<Placemark>
<name>
Big Triangle</name>
<styleUrl>
#stdstyle</styleUrl>
<Polygon>
<outerBoundaryIs>
<LinearRing>
<coordinates>
-76, 41,0
-75, 40,0
-77, 40,0
-76, 41,0
</coordinates>
</LinearRing>
</outerBoundaryIs>
</Polygon>
</Placemark>

(Screenshot from Google Earth)

(Figure 2.1)

Using the KML code above to create the triangle above:

Line Start Coord End Coord Equation Result
1 -76, 41 -75, 40 ((-75)-(-76))(40+41) 81
2 -75, 40 -77, 40 ((-77)-(-75))(40+40) -160
3 -77, 40 -76, 41 ((-76)-(-77))(41+40) 81
Total: 2



KML code:

<Placemark>
<name>
Small Triangle</name>
<styleUrl>
#stdstyle</styleUrl>
<Polygon>
<outerBoundaryIs>
<LinearRing>
<coordinates>
-76, 40.75,0
-76.5, 40.25,0
-75.5, 40.25,0
-76, 40.75,0

</coordinates>
</LinearRing>
</outerBoundaryIs>
</Polygon>
</Placemark>

(Screenshot from Google Earth)

(Figure 2.2)

Using the KML code above to create the triangle above:

Line Start Coord End Coord Equation Result
1 -76, 40.75 -76.5, 40.25 ((-76.5)-(-76))(40.25+40.75) -40.5
2 -76.5, 40.25 -75.5, 40.25 ((-75.5)-(-76.5))(40.25+40.25) 80.5
3 -75.5, 40.25 -76, 40.75 ((-76)-(-75.5))(40.75+40.25) -40.5



Total: -0.5



There is also a really good flash based demo on how this works available online here: http://www.mechanisms101.com/greens_theorem_demo.html

Posted by & filed under Uncategorized.

So the Ben Franklin Bridge is awesome to bike over.  I did it not too long ago so I could explore Camden.  The people I met over there were all very nice, but I did meet a dog over there that probably was going to kill me.  Luckily its owner was able to restrain the beast from having me for dinner.

In any case, Bike Week (not this Bike Week) is next week, and they’re going to keep the bridge opened until 11pm! Just keep in mind that it’ll be dark, and there are parts of the walkway where you’re really not supposed to bike, and I can only imagine they’ll be more dangerous when you can’t see anything.

Enjoy!

Philadelphia Bicycle News: Ben Franklin Bridge Extends Hours For Bike Week.

Posted by & filed under Uncategorized.

Hmmm, Jerry A wonders, Im not sure my disc will get back to them with this.

"Hmmm," Jerry A wonders, "I'm not sure my disc will get back to them with this."

I wonder where 99999-9999 would be.  The highest ZIP Code is 99950 in the extreme southeastern part of Alaska, including the City of Ketchikan, AK. 99999 is reserved for special uses only.  Sorry Netflix.

#No Data (via The Daily WTF)

Posted by & filed under GIS.

I love heat maps, and I think OpenStreetMap.org is an amazing idea.  This is a heat map of the tile usage.  It’s cool to see bright spots in South America and Africa.  I’m curious as to why there isn’t a bright spot near Perth, and I guess I’ll need to sign in to get info on New Zealand, Eastern Australia, and Alaska. What’s with these maps that are always cutting on the Water Hemisphere anyway?

m.k.ge•o•mat•ics |ˌjēəˈmatiks| › CloudMade Tile Request Graphics.

Posted by & filed under Bicycle.

Why are bicycles banned from the Experimental Prototype Community of Tomorrow?  Walt Disney is known for futuristic ideas for transportation such as the Monorail and the PeopleMover.  Walt Disney failed to envision a world utilizing the most energy efficient mode of transportation: the bicycle.

John from the Philadelphia Bicycle News writes about his plans to go to Disney World, and how he wishes there were a more bikable option for him.

Philadelphia Bicycle News: What If Walt Disney Rode A Bike?.