awk scripting to select a rectangle frame


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# 8  
sorry, I don't think I can help - not sure of the algorithm and you're not providing any hints.
Maybe other did better in their trigonometry in school.
Would be interesting to see the attempts/solutions.

Also...
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Last edited by vgersh99; 02-16-2020 at 01:57 PM..
# 9  
Hi jeo_fb...

Assuming you are using Longitude and Latitude WRT Earth as a __sphere__ then it is not possible to create a rectangle as Euclidean geometry does not apply.

IF, however you just want the Longitude to change but have matching Latitudes and vice versa and those listing out then please confirm...

Bazza...

Last edited by wisecracker; 02-17-2020 at 07:01 AM.. Reason: Add the words "and vice versa"
# 10  
I pretty sure it is possible to take latitudes and longitudes and construct a 2D geometric shape (like a rectangle) if we know the distance from the center of the coordinate system (commonly called "the elevation" above mean sea level of the earth). Otherwise, land surveying would not be possible since surveying is based on longitude and latitude (coordinates) with the elevation (on the Earth this is the distance above MSL).

Latitude and longitude, along with distance from the center of the earth, form polar coordinates, as I fondly remember from "the good ole days" when I worked as a land surveyor (actually I had my own land surveying business for many years),

The problem I have with this question is that the OP is not providing his algorithm as vbe mentioned in post #8.

So, let's ask the OP to post his formulas (algorithms) he is using to do the calculations.

The short answer is "to select a rectangle frame from longitude and latitude" is that you need to know the distance from the center of the coordinate system for each coordinate. This is simply a problem in converting polar to rectangular coordinates, and back.

Of course, you know me, I have done this kind of calculation countless times (in my youth) and never did it with awk. I used to do these calculations (almost daily) on the Tandy TRS 80 which I programmed in Basic and also the Atari / Amiga, back in the "day".

Last edited by hicksd8; 02-17-2020 at 10:38 AM..
# 11  
- an area solution ex.:
Code:
awk '
function triangle_area(x1, y1, x2, y2, x3, y3) {
#
# determine area of triangle with the 3 points given
#
area=((x1 * (y2 - y3) + x2 * (y3 - y1) + x3 * (y1 - y2)) / 2.0);
#
# return absolute value of area. area value should be positive. unless you are on drugs.
#
return area < 0 ? -area : area;
}
FILENAME ~ /rectangle/ {
if (! repeat_line[$0]++) {
#
# load points of rectangle in x, y arrays.
#
x[NR]=$1;
y[NR]=$2;
} else {
#
# repeat line found so rectangle is closed. that is nice.
# calculate area of rectangle by adding area of two triangles that make up rectangle
#
Rectangle_area=triangle_area(x[1], y[1], x[2], y[2], x[3], y[3]) + triangle_area(x[1], y[1], x[3], y[3], x[4], y[4]);
}
}
FILENAME ~ /positions/ {
#
# determine area of 4 triangles made up of latitude, longitude point and each side of rectangle
#
triangle1=triangle_area(x[1], y[1], $1, $2, x[2], y[2]);
triangle2=triangle_area(x[2], y[2], $1, $2, x[3], y[3]);
triangle3=triangle_area(x[3], y[3], $1, $2, x[4], y[4]);
triangle4=triangle_area(x[1], y[1], $1, $2, x[4], y[4]);
#
# if rectangle area equals to total area of 4 triangles then point is inside rectangle. it is obvious if you think about it.
#
if (Rectangle_area==triangle1+triangle2+triangle3+triangle4) print $0;
}
' rectangle positions

note, example posted uses format of input/output files shown (not csv, as stated).

Last edited by Neo; 02-28-2020 at 01:17 AM..
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