Poly-Build issue with extreme West-East Area

[pablo_saenz]

Hi,

I have an Excel file with the latitude and longitude of an area I need to build in Alteryx using the poly-build tool, as well as the point order. This is how the points in a map and the data looks like:

 But when I use the Poly-Build tool, because the points are at the West-East end, it seems that Alteryx doesn't recognise it properly, and it doesn't create the circle (like if the Earth wasn't round...). And it connects the points crossing all the Earth!

This is a big issue, because I have to perform some spatial match analysis, but of course the area is not build correctly. The area should be just a circle. And the point order is correct, I check it several times.

Any ideas how to solve this or it's a bug?

Thanks,

Pablo

[JeradR]

Hi @pablo_saenz,

I was able to replicate your issue, but I may have a workaround.  If you draw straight lines from one point to all other points and measure the length of the lines, the longest line should be your diameter (or very close to it).  You can then take the midpoint of the aforementioned line and use the buffer tool to construct a radius equivalent to your expected output.  Please see attached example.

@RobertB - Is this issue expected?

[RobertB]

This behavior is expected, because the PolyBuild tool doesn't know you're building a circle, it's just connecting the dots, and in our polygon spatial objects, regions don't cross the 180/-180 line. Instead that circle needs to be represented by a two region polygon, one for the part on either side of the line.

If you can get the center point and radius, using the trade area tool to generate the circle is probably the easiest way.  Note that if you look at the polygon that that trade area tool generates, it will have two regions, one on each side of the line.  

[pablo_saenz]

Hi,

thanks both for your replies and apologies for the delay replying. Unfortunately this doesn't solve my issue because I don't need to build 1 polygon, I need to build a lot of them that are not circles necessary.

I understand that this behavior is expected, but should it be? At the end it is working like if the Earth wasn't rounded, what doesn't make many sense. At the end the PolyBuild should know that I'm building a polygon, and I'm giving the tool the order so should be able to create it properly in my opinion. And there are a lot of industries that I assume have this same need (maritime, aviation, etc).

Thanks,

Pablo

[Balders · Accepted solution]

Hey Pablo,

To get around this "expected behaviour" I've created a workflow that splits the polygons into two if they cross from east to west.

The required fields here are:

- PolygonID

- Point Order

- Longitude

- Latitude

and you need to make sure the data wraps around so the last point has the same geography as the first point in a polygon.

From here the general gist of the workflow is:

- Calculate if East-West crossings happen

- Pad data to insert two new points either side of crossings

- Calculate the positions for these points using multi-row formulae

- Create new polygon IDs with A/B denoting if a polygon was split

- Build the polygons

[pablo_saenz]

Thanks! That worked really well.

[JeradR]

@Balders - Outstanding work!

[derekbelyea]

Great solution but REALLY  it should not be this hard.