Hi, 

I noticed that sometimes the area highlighting feature of SkyDemon generates self-intersecting polygons. For example, this NOTAM:

D) DAILY 1600 - 2130
E) NIGHT VFR TRAINING FLIGHTS (NVG OPS)
BURGENLAND AREA OBERWART:
473120N 0161150E
472750N 0163820E
470250N 0160720E
470050N 0162850E
START HELIPORT OEAMTC OBERWART LODO
PARTICIPATING HELICOPTER: OEXEK OR OEXEQ (EC 135) MONITORING
134,675MHZ
F) GND G)2500FT AGL

is displayed as a self-intersecting polygon - see the images in this gallery: http://imgur.com/a/Sx3i8

I assume this happens due to the order of the vertices (coordinates) in the NOTAM - I think this feature would look much nicer if there was some algorithm involved which can detect this condition and re-order the vertices 

Kind regards
Martin

If a NOTAM is published with a list of coordinates that result in a self-intersecting polygon, then SkyDemon will display a self-intersecting polygon. We do not want to try to be too "clever" and rearrange vertices until we get something that doesn't self-intersect.

It seems to me that the problem here is with the original NOTAM - the coordinates are published in the wrong order.

Thanks, that makes sense to me. I didn't know there was a guideline for drawing polygons in NOTAMs (Google found this document, see page 2-55) which even says that a polygon shall be closed by specifying the first coordinate as the last entry in the list, so even if the hourglass shape was intended, they did not fully follow these guidelines...

Since the "polygon" is not closed, do you think perhaps it was intended to be a route (or linear feature) rather than an area, as the text indicates?

I sent them an e-mail and asked for clarification: it was intended to be the non-intersecting area shown in my second picture. They have since fixed the order of the vertices, but still do not properly close the polygon, so now it looks like this in SkyDemon:

http://imgur.com/a/GzJ9Q

This is the updated NOTAM:

B) 1609161600 C)1609182130 (B1316/16)
D) DAILY 1600 - 2130E) EXERCISE WILL TAKE PLACE AT AREA OBERWART WITHIN AUSTRIAN TERRITORY. NIGHT VFR TRAINING FLIGHTS (NVG OPS) BURGENLAND AREA OBERWART:
473120N 0161150E (KRUMBACH)
472750N 0163820E (LUTZMANNSBURG)
470050N 0162850E
470250N 0160720E (FUERSTENFELD)
START HELIPORT OEAMTC OBERWART LODO
PARTICIPATING HELICOPTER: OEXEK OR OEXEQ (EC 135) MONITORING 134,675MHZ
STRAIGHT LINE DEFINED BY:
473120N 0161150E
472750N 0163820E
470050N 0162850E
470250N 0160720E
F) GND G)2500FT AGL

They've made it worse, it would seem. They are now attempting to describe two geographical objects (an area and a route) in one NOTAM which is fraught with the potential for error. Graphical depiction of NOTAM is never perfect because the NOTAM system wasn't designed in that way, but SkyDemon will normally get it right as long as the source data is good. A polygon is generally fine; a line is generally fine; mixing the two is unlikely to work.