My Impervious Surface Unit mapping utility now selects other ISUs based on distance!

Well, I did manage to integrate that new search/distance function into the program. You can see the function I used in the previous post. This function allows you to compute the distance between two points with WGS 1984 coordinates (the kind you get from your GPS device, i.e. 47.854N -122.458E). What it outputs is the distance in miles.


So, for the program I just told it to do a search between two points, the first point being the center point for a particular parcel, and the second points being an array of data that contained all of the center points for all of the other properties in Bremerton. So now, when I perform a query, the computer not only plots the polygon that I asked it to show: but also the polygons for all properties within .05 miles (about 300ft). This is why you can see in the image below that the impervious surfaces displayed are in a rough circle around the selected property. I wanted to differentiate between the two, so I made the highlighted property colored and the rest of the properties grayish.

There is variance in the color of the grayed properties: some are darker than others. This is because some ISU’s have more than one match, so they get colored twice and are therefore darker. I need to go back and clean up the duplicates to correct for this, or make the matching direct instead of joined. The reason that some parcels that should be there around the edge are missing is because sometimes the center point of the ISU in question doesn’t lay within the search criteria, and so that ISU doesn’t get selected.

I used arcMAP to determine the center point of each parcel. To do this, I just added two fields to the ISU attribute table CenterX and CenterY. These had properties of double (15,10), which gave me lossless entry of all of the coordinate data. I then used the field geometry tool, and selected x-coordinate of centroid and y-coordinate of centroid and entered them into the appropriate fields, saved and reuploaded to the MySQL database for use.

Even with all this new programming, the whole utility still runs fast. Indexing the columns has improved the speed of the program immensely. Indexing doesn't help with the new function though, since the calculations have to be performed for each center point in the dataset each time a new ISU is selected. But, not only does the distance calculating formula work, but I was able to successfully use it to create a new function within the program I was creating. Highly recommended.

The newest version of the utility also includes links to the parcel owner / property information within the Kitsap County database. Also, each of the adjacent properties have the option of being selected to become the new center property (by recentering), which allows you to find details about adjacent accounts pretty easily. This added functionality is going to make this a real slam-dunk for Utility Billing if they can find a way to use it in time.

Dom

Here was the actual SQL statement I used to find the adjacent parcels:


$querycenter = "SELECT AccountNum,((ACOS(SIN($lat * PI() / 180) * SIN(tbl_ISU.Centery * PI() / 180) + COS($lat * PI() / 180) * COS(tbl_ISU.Centery * PI() / 180) * COS(($lon - tbl_ISU.Centerx) * PI() / 180)) * 180 / PI()) * 60 * 1.1515) AS distance FROM tbl_ISU having distance<= '.05' ORDER BY distance limit 0,500";
$resultcenter = mysql_query($querycenter);


The limit is just so that the thing doesn't timeout if it finds too many properties.