Subject: [Geopriv] DISCUSS on draft-ietf-geopriv-policy (Russ Housley)

From: Hannes Tschofenig <[email-masked]>
Date: Tue, 25 Sep 2007 13:18:03 +0200

Here is Russ's DISCUSS:
https://datatracker.ietf.org/idtracker/draft-ietf-geopriv-policy/comment/71948/
https://datatracker.ietf.org/idtracker/draft-ietf-geopriv-policy/comment/71949/

"
In section 6.5.2, the values in the table for n=38.89868 do not seem
  right.  Working through the most simple case, where r=1.0, I get:
 
    39.39868 = n*r + 0.5
    39.00000 = FLOOR(n*r + 0.5)
    39.00000 = FLOOR(n*r + 0.5) * 1/r
"

"
  Consider a the four corners of Colorado.  (Colorado is a rectangle.)
  Call the northeast corner A.  Call the northwest corner B.  Call the
  southwest corner C.  Call the southeast corner D.  It is pretty clear
  that ABCDA is a valid polygon.  Is ACBDA a valid polygon?  I do not
  see text that would tell me that such a polygon is not allowed, but
  such text could be in EPSG 4326 or EPSG 4979.  I did not go look.  I
  have writen algorithms to find a polygon that includes all of the
  provided coordinates, but that does not seem like the right thing
  to do here. 

  The formula:
      n'=FLOOR(n*r + 0.5) * 1/r
  Can be simplified to:
      n'=FLOOR(n*r + 0.5)/r
"

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From: "Thomson, Martin" <[email-masked]>
Date: Tue, 25 Sep 2007 18:57:21 -0500

On the second comment only ('though I agree with the first)...

>   provided coordinates, but that does not seem like the right thing
<snip formula (first comment?)>

Good pick-up.

I think that it would be a good idea to reference pidf-lo-profile for rules on polygon construction.  I believe that the text here is cloned to avoid a dependency problem.  A reference would avoid this problem.

Here is what pdif-lo-profile (sic) says:

"
   A connecting line SHALL NOT cross another connecting line of the same
   Polygon.

   Polygons SHOULD be defined with the upward normal pointing up, this
   is accomplished by defining the vertices in counter-clockwise
   direction.

   Points specified in a polygon MUST be coplanar, and it is RECOMMENDED
   that where points are specified in 3 dimensions that all points
   maintain the same altitude.
"

Making the same altitude restriction mandatory is the only difference I can see here.

Regards,
Martin

p.s. By pdif-lo-profile, ADCBA isn't recommended either because it is in clockwise order.

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