Re: Ellipses

To be more accurate, an OMEllipse with axis as lengths would have to do
a couple of things.

The OMCircle in lat/lon space with a length radius creates a lat/lon
polygon in segments around the center, with all points the same ground
distance away from the center. It uses the GreatCircle class for that.

An ellipse would have to do the same thing, except the ground distances
away from the center would have to be calculated for the different
segment nodes. Then in the same way as the circle, you would use the
GreatCircle class to calculate the actual lat/lon points of the polygon
segments.

If you rotate the ellipse, then that has to be taken into account for
the GreatCircle calculations.

That's one brute force approach. I'm sure that there is a more elegant
one out there.2

- Don

On Thursday, September 26, 2002, at 03:20 PM, Jamie Oldham wrote:

> Here's how i calculate the width and height, it is in the layer so it
> is
> called when appropriate..
>
> // Project the lower right lat/lon coordinates to screen coordinates
> Point lowerPoint = proj.forward(
> (float)box.lowerRightCorner.latitude,
> (float)box.lowerRightCorner.longitude);
>
> // Project the upper left lat/lon coordinates to screen coordinates
> Point upperPoint = proj.forward(
> (float)box.upperLeftCorner.latitude,
> (float)box.upperLeftCorner.longitude);
>
> // Calculate the diameter of the fix ellipse
> diameterX = (int)Math.abs(upperPoint.getX() - lowerPoint.getX());
> diameterY = (int)Math.abs(upperPoint.getY() - lowerPoint.getY());
>
>
>
> -----------------------------------------------------------------------
> -----
> ----
>
> The bounds of the ellipse box can be calulated with the following ;
>
> public Box CalculateEllipseBox (Location ellipseCenter,
> double majorAxis,
> double minorAxis,
> double orientation)
> throws MathError,
> LocationTooCloseToPole {
>
> Box box = new Box();
> Location upperMajorAxisEndpoint = new Location();
> Location lowerMajorAxisEndpoint = new Location();
> Location leftBoxPoint = new Location();
> Location rightBoxPoint = new Location();
> Location highestBoxPoint = new Location();
> Location lowestBoxPoint = new Location();
> double majorAxisBearing;
> double minorAxisBearing;
> double majorAxisLength;
> double minorAxisLength;
>
> majorAxisLength = Math.abs (majorAxis);
> minorAxisLength = Math.abs (minorAxis);
>
> if (Math.abs (orientation) <= 90.0)
> majorAxisBearing = orientation;
> else
> majorAxisBearing = orientation + 180.0;
>
> upperMajorAxisEndpoint = CalculateDestination (ellipseCenter,
> (majorAxisLength / 2.0), majorAxisBearing);
>
> lowerMajorAxisEndpoint = CalculateDestination (ellipseCenter,
> (majorAxisLength / 2.0), (majorAxisBearing + 180.0));
>
> if (majorAxisBearing >= 0.0) {
> minorAxisBearing = NormalizeBearing( majorAxisBearing + 270.0);
>
> rightBoxPoint = CalculateDestination (upperMajorAxisEndpoint,
> (minorAxisLength / 2.0), (minorAxisBearing + 180.0));
>
> leftBoxPoint = CalculateDestination (lowerMajorAxisEndpoint,
> (minorAxisLength / 2.0), minorAxisBearing);
> } else {
> minorAxisBearing = majorAxisBearing + 90.0;
>
> rightBoxPoint = CalculateDestination (lowerMajorAxisEndpoint,
> (minorAxisLength / 2.0),
> minorAxisBearing);
>
> leftBoxPoint = CalculateDestination (upperMajorAxisEndpoint,
> (minorAxisLength / 2.0),
> (minorAxisBearing + 180.0));
> }
>
> highestBoxPoint = CalculateDestination (upperMajorAxisEndpoint,
> (minorAxisLength / 2.0),
> minorAxisBearing);
>
> lowestBoxPoint = CalculateDestination (lowerMajorAxisEndpoint,
> (minorAxisLength / 2.0),
> (minorAxisBearing + 180.0));
>
>
> Location northPole = new Location();
> northPole.latitude = NORTH_POLE_LATITUDE;
> northPole.longitude = NORTH_POLE_LONGITUDE;
>
> Location southPole = new Location();
> southPole.latitude = SOUTH_POLE_LATITUDE;
> southPole.longitude = SOUTH_POLE_LONGITUDE;
>
> if (DistanceBetween (ellipseCenter, northPole) <= (majorAxisLength /
> 2.0))
> {
>
> box.upperLeftCorner.latitude = MAX_LATITUDE;
> box.upperLeftCorner.longitude = MIN_LONGITUDE;
> box.lowerRightCorner.longitude = MAX_LONGITUDE;
> box.lowerRightCorner.latitude = lowestBoxPoint.latitude;
>
> } else if (DistanceBetween ( ellipseCenter, southPole) <=
> (majorAxisLength / 2.0)) {
>
> box.upperLeftCorner.latitude = highestBoxPoint.latitude;
> box.upperLeftCorner.longitude = MIN_LONGITUDE;
> box.lowerRightCorner.longitude = MAX_LONGITUDE;
> box.lowerRightCorner.latitude = MIN_LATITUDE;
>
> } else {
> box.upperLeftCorner.longitude = leftBoxPoint.longitude;
> box.upperLeftCorner.latitude = highestBoxPoint.latitude;
> box.lowerRightCorner.longitude = rightBoxPoint.longitude;
> box.lowerRightCorner.latitude = lowestBoxPoint.latitude;
>
> }
>
> return box;
>
> }
>
>
>
> jo
> ----- Original Message -----
> From: "Oscarson Erik" <eoscarson@rayva.org>
> To: "Jamie Oldham" <joldham@modusoperandi.com>; <openmap-users@bbn.com>
> Sent: Thursday, September 26, 2002 2:05 PM
> Subject: RE: Ellipses
>
>
>> Hi Jamie,
>>
>> I'm not sure this will help. Does whatever calls this method keep
>> track
>> of the georeferenced points and then call projection.forward(...) to
>> get
>> the appropriate Height & Width?
>>
>> This uses the same constructor that I mentioned. The width & height
>> are
>> X/Y window coordinates, so the ellipse is always the same size
>> regardless of map scale or projection, unless the width & height that
>> are passed in have been 'generated' in some way.
>>
>> If you want to see some real OpenMap 'magic,' create a LatLon OMCircle
>> using straight lines and then use the gestures mode to drag it around
>> the map window that uses CADRG-projection. The circle projects
>> correctly in real-time. If you were able to try the same thing with
>> an
>> ellipse, the size/shape wouldn't change, no matter where it was moved
>> to.
>>
>> Erik
>>
>>
>> -----Original Message-----
>> From: Jamie Oldham [mailto:joldham@modusoperandi.com]
>> Sent: Thursday, September 26, 2002 12:40 PM
>> Subject: Re: Ellipses
>>
>> Hey,
>>
>> I currently use the following code to create ellipses using OpenMap,
>> it
>> works great!
>>
>> /**
>> * Create the ellipse
>> * @return OMCircle
>> * The fix ellipse
>> */
>> public OMCircle createCircle(float centerLat, float centerLon,
>> int width, int height, double angle, Color color) {
>> OMCircle circle = new OMCircle(centerLat, centerLon,
>> width, height);
>> circle.setRotationAngle(angle);
>> circle.setLinePaint(color);
>> return circle;
>> }
>>
>>
>> jamie oldham
>>
>>
>> ----- Original Message -----
>> From: "Pearson John T Jr GG-13 453 EWS/EWR"
>> <John.Pearson@LACKLAND.AF.MIL>
>> To: "'Oscarson Erik'" <eoscarson@rayva.org>; <openmap-users@bbn.com>
>> Sent: Thursday, September 26, 2002 11:42 AM
>> Subject: RE: Ellipses
>>
>>
>> Classification: UNCLASSIFIED
>>
>> On Thursday, September 26, 2002 10:14 AM, Erik Oscarson wrote
>>
>>> There is a good possibility that I've missed something that already
>> exists
>> within the API.
>>
>> Perhaps someone else has developed what you need, and would be willing
>> to
>> share it with all of us OpenMap users/developers.
>>
>> Regards
>>
>> John pearson
>>
>>
>> -----Original Message-----
>> From: Oscarson Erik [mailto:eoscarson@rayva.org]
>> Sent: Thursday, September 26, 2002 10:14 AM
>> To: openmap-users@bbn.com
>> Subject: Ellipses
>>
>>
>> Hi All,
>>
>> I'm trying to use OMCircle to create ellipses that have major and
>> minor
>> axes
>> that use Length, like the
>> OMCircle constructor [OMCircle(float latPoint, float lonPoint, float
>> radius,
>> Length units)] uses for radius.
>>
>> I'm not sure if this is a good approach or not, but I am planning on
>> extending the OMCircle class (OMEllispe maybe?) and setting something
>> up
>> that would simply derive the H/W from the projection during generation
>> and
>> then use that to rebuild itself as necessary. This approach is
>> geographically unsound, but at smaller zoom levels it might work well
>> enough.
>>
>> I do not have knowledge of the math necessary to do this correctly,
>> but
>> I'm
>> still going to play around with it.
>>
>> There is a good possibility that I've missed something that already
>> exists
>> within the API.
>>
>>
>> Erik Oscarson
>> Raytheon
>> eoscarson@rayva.org
>>
>>
>> --
>> [To unsubscribe to this list send an email to "majdart@bbn.com"
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>>
>> Classification: UNCLASSIFIED
>>
>> --
>> [To unsubscribe to this list send an email to "majdart@bbn.com"
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>>
>>
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>
>
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>

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Don Dietrick, BBN Technologies, dietrick@bbn.com
10 Moulton Street, Cambridge, MA 02138
617-873-3031 [fax]-2794
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