Problems with finding angles with different signs

[roldy]

I need to find all angles that are greater than 90. To be more precise I need to find the entries that are to the right of the blue line and to the right of the red line. I tried using the the find command in MATLAB to find certain indices but realized that the angle signs change. The blue and red lines are points on the curve where the angle is zero. The point of zero angle is not known. The reason for this is that I need this to work for a general case, meaning that I want to factor in an attack angle. This means that the green line will not be horizontal. I've included a picture of the shape of the vehicle and a close up of the top and bottom of the curve. I have also included an excel file with the angles as well as the .m file for the slope and angle calculation. Also, the green line is located at x=0.

all files are zipped here:
http://www.mediafire.com/?d5tcj7dceq54fwi

right of blue line: negative
left of blue line to above green line: positive
bottom of green line to left of red line: negative
right of red line: positiveshould I just add 90 degrees to the angles so that the angle the green line makes with the tangent of the curve is 90. This has to be for a general attack angle also. Meaning that the green line is not horizontal.

 

[NateD]

Yes, you can add 90 degrees to all the angles so that the angle the green line makes with the tangent of the curve is 90. This should work for any attack angle. For example, if the angle of the green line is -30 degrees, you should add 120 degrees to all the angles (90 + (-30)). This will ensure that the angles you find are greater than 90.