# Re: [OpenMap Users] Determining the lat / long coordinates of a point that is a known distance from a known other point?

From: David Ward <synriga_at_yahoo.com>
Date: Fri, 11 Aug 2006 13:18:09 -0700 (PDT)

Chris,

Based on what I think you want to do from your description, I would use an OMArc.

Assuming you sensor has a fixed range, you can create an OMArc with the radius set to sensor:range. You can define the arc angle as 30 degrees center on 0 degrees to represent the sensor's field of view. And then use setRotationAngle() to change the orientation for the field of view is pointed in the desired direction. This is a brute force way of handling it. A more eligant was is to create your own OMGraphic that keeps itself updated based on the sensor and target attributes.

Cheers,
David

----
David Ward
ROLANDS & ASSOCIATES Corporation
500 Sloat Avenue
Monterey, CA 93940
USA
Tel: 1.831.373.2025
Fax: 1.831.373.2841

----- Original Message ----
From: "Esposito, Christopher" <christopher.esposito_at_boeing.com>
To: openmap-users_at_bbn.com
Sent: Friday, August 11, 2006 11:31:07 AM
Subject: [OpenMap Users] Determining the lat / long coordinates of a point that is a known distance from a known other point?

Hello, All-
I have the coordinates of 2 points Lat1, Long1 (which represent
a sensor) and Lat2, Long2 (which represent a target. The sensor has a
field of view of 30 degrees, and we currently assume that the target is
centered in the sensors' field. What I would like to do is construct and
draw a triangle (an OMPoly) with the sensor location at the apex of the
triangle and the target location at the center of the base, so that a
line from sensor to target bisects the triangle.

1) If this triangle was in Euclidean geometry, then the distance between
the two points and the known angle (15 degrees) between the hypotenuse
and the bisection line from sensor to target, plus a bit of
trigonometry, would allow me to calculate the distance between the
target location at the midpoint of the base and the other 2 corners of
the triangle at either end of the base.

2) The spherical_distance method in the GreatCircle class seems to me to
be the right method for calculating the distance between the two points
on a sphere (right?). This method says it returns a float - what units
(miles, meters, etc.) is this number in?

3) if I use the method from (1) and the distance from (2) to calculate
the distance from the target to the other 2 corners that define the base
of the triangle, what OpenMap method call will give me the coordinates
of these points given their distance from a known point? I've looked
through a few projection-related classes, but my knowledge of
projections and spherical geometry is limited enough I'm not sure I
would recognize the answer if I saw it.

Thanks,
Chris

Chris Esposito, Ph.D.
Associate Technical Fellow
Boeing
(425) 373-2788

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Received on Fri Aug 11 2006 - 16:25:50 EDT

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