idea Add "Vincenty" formulas to the Python getArea method in ArcGIS Pro Ideas

Add "Vincenty" formulas to the Python getArea method

GregHollard — Tue, 02 Jul 2024 21:17:07 GMT

We use extensions by Jeff Jenness to help create accurate and consistent area values for some pretty large features, but it would solve some integration issues if the Vincenty distance and area formulas could be added to the list of options to the python methods for area and distance.

The differences for an example polygon are shown below. The differences is small, but significant enough to make a difference.

Currently the options for the getArea method are :

PLANAR
GEODESIC
GREAT_ELLIPTIC
LOXODROME
PRESERVE_SHAPE

It would be great if we could do this:

!Shape!.getArea("VINCENTY","HECTARES")!

Thanks also to Dan Mahr‌ for a great article about Calculating Geodesic Areas

Re: Add "Vincenty" formulas to the Python getArea method

DanPatterson_Retired — Wed, 25 Jan 2017 02:56:15 GMT

hmmm /blogs/dan_patterson/2017/01/24/vincenty ... distance done, shouldn't be to hard to extend

Re: Add "Vincenty" formulas to the Python getArea method

MelitaKennedy — Wed, 25 Jan 2017 17:51:40 GMT

When I see spherical as part of the name, I assume that a sphere is being used as the model of the Earth. If that's the case, I would expect different results. According to the help document for his Tools for Graphics and Shapes, the tool converts a spheroid/ellipsoid to a sphere of equal volume (p73). To calculate areas, I would expect a conversion to an authalic sphere instead--same surface area.

Re: Add "Vincenty" formulas to the Python getArea method

GregHollard — Thu, 26 Jan 2017 00:29:47 GMT

I can see your point, but I'm not in a position to argue with either the legal process that requires these functions to be used or with the research done to produce the functions in the first place. I'm just looking for the best way to include these functions in the ArcGIS Platform so we can streamline our processes.

Re: Add "Vincenty" formulas to the Python getArea method

DanPatterson_Retired — Thu, 26 Jan 2017 01:21:02 GMT

Maybe Melita Kennedy‌ could comment on this link to see if it would be the proper implementation or a variant

Algorithms for geodesics | SpringerLink

or it you could provide the link to Jeff's implementation, translating from Avenue if they were from ArcView 3.x wouldn't be a problem

Re: Add "Vincenty" formulas to the Python getArea method

BruceHarold — Thu, 26 Jan 2017 14:49:57 GMT

I have used Vincenty distance from a Python module, see this sample for Pro:

http://www.arcgis.com/home/item.html?id=da9efbe1232f426ead182213f53c8cd8

Re: Add "Vincenty" formulas to the Python getArea method

DanPatterson_Retired — Thu, 26 Jan 2017 18:37:47 GMT

I have yours linked on my blog, there are several incarnations for distance... the implementation I used was nice since students could follow along with the formula and the code and see how they related. The only problem with that one, is it uses an iterative solution, which is ok. The reference link I posted is supposed to be non-iterative, but the equations would make a mathematicians head bleed, so I was curious to see what esri used for area which is less well documented

Re: Add "Vincenty" formulas to the Python getArea method

MelitaKennedy — Thu, 26 Jan 2017 21:43:14 GMT

It's fine. I'm not up on the math, but there's a mention of an authalic sphere, so my guess is that Karney is doing a similar solve-triangles but on a equal surface area sphere. I think it's probably more accurate than Jenness. When my colleague was looking at doing direct area calculation on an ellipsoid, he couldn't get a stable implementation. We're using a mix of geodesic calculations and ellipsoid-based equal area projections.

Greg Hollard‌ Was the data in a pcs when you ran the planar getArea calculation? If so, what was it? If it wasn't equal area, could you run it again for me? Could you explain further about the legal ramifications? Is there legislation that Jenness's method must be used? Or that the same method used previously must be used? Or? Thank you!

Melita

Re: Add "Vincenty" formulas to the Python getArea method

GregHollard — Thu, 23 Mar 2017 00:33:48 GMT

Hi Melita,

The data is projected in the New Zealand Transverse Mercator Projection.

The legal ramifications have to do with the calculation of fees for permits. A lot of work was done to select a process that would give a consistent value for areas within the 5.7 million square kilometres of our Exclusive Economic Zone and extended continental shelf.

Greg

Re: Add "Vincenty" formulas to the Python getArea method

BruceHarold — Thu, 23 Mar 2017 15:37:46 GMT

Greg, Melita is out until the 27th.

Re: Add "Vincenty" formulas to the Python getArea method - Status changed to: Closed

HannesZiegler — Tue, 29 Oct 2024 14:18:31 GMT

Thank you for submitting your idea to add Vincenty to distance and area calculation methods of Geometry objects. We appreciate your suggestion and the time you took to provide detailed feedback. However, after carefully evaluating the request, we have decided against this for several reasons.

1. Vincenty did not publish formulas for area calculations.

2. The area method published by Jeff Jenness in the Tools for Graphics and Shapes manual is less accurate than our methods (see notes on page 19, where method assumes sphere for spheroid). The preserve_shape and geodesic methods of getArea are the most accurate.

3. Vincenty length is given with the geodesic method for getLength.

After careful consideration, we regret to inform you that we will not be implementing this idea at this time.

Thank you again for your contribution and understanding, and apologies for our long delay in answering. Let us know if you have further questions.