eqfilter polygon definition

Victor Preatoni

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Jan 2, 2024, 12:14:58 PMJan 2

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Hi,

I am facing a problem with the polygon definition for eqfilter. Some events that fall inside a polygon get discarded.

My definitions from log file are as follows:

Inst 186 - 5 Inclusion regions
Reg 0 (4): [-38.00, -70.80] [-38.00, -71.30] [-37.70, -71.30] [-37.70, -70.80] [-38.00, -70.80]
Reg 1 (4): [-39.80, -71.20] [-39.80, -71.70] [-39.50, -71.70] [-39.50, -71.20] [-39.80, -71.20]
Reg 2 (4): [-36.30, -70.20] [-36.30, -70.70] [-35.90, -70.70] [-35.90, -70.20] [-36.30, -70.20]
Reg 3 (4): [-36.90, -70.10] [-36.90, -70.80] [-36.50, -70.80] [-36.50, -70.10] [-36.90, -70.10]
Reg 4 (4): [-63.10, -60.30] [-63.10, -60.90] [-62.80, -60.90] [-62.80, -60.30] [-63.10, -60.30]

And here are a couple of events that clearly would fall inside polygon Reg 2, but are ignored:

Inst 186, coords -36.04, -70.68 ==> not in any InclRegion ==> IGNORING.

Inst 186, coords -36.16, -70.55 ==> not in any InclRegion ==> IGNORING.

Anyone has faced same problem before??. Maybe the problem is with southern latitudes only?.

Thanks,

Victor

Mitchell M Withers (mwithers)

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Jan 2, 2024, 3:52:54 PMJan 2

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It works with negative longitudes so should also work with negative latitudes though I'm not sure that's well tested. Does the inst_id for the rejected events match the inst_id of the configured include region? If not, it would be rejected whether in the polygon or not, unless AllowUndefInst is enabled.

Mitch

Center for Earthquake Research and Information (CERI)
University of Memphis
Memphis, TN 38152
901-678-4940

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Victor Preatoni

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Jan 3, 2024, 9:24:49 AMJan 3

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Hi Mitch,

Inst Id matches. In the log I can see that the polygon definitions are for Inst 186 (INST_OAVV), and that the rejected locations arrive with Inst 186 too.

I have faced the same problem before with ewhtmlemail regions, but at that time I thought it was a problem with my configuration. Now that problem arises again, I will do some manual code tests on the geom_area C function defined in geom.c to debug it. Both modules (eqfilter & ewhtmlemail) use the same function.

Will keep group updated on test results.

Thanks!,

Victor

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Victor Preatoni

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Jan 3, 2024, 11:00:49 AMJan 3

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I can confirm there is a bug in geom_area() function used in eqfilter.c and ewhtmlemail.c.

Function is defined in geom.c

Although I have not tested eqfilterII, it uses area.c file, which seems to use the same algorithm as geom.c.

Test I have done so far:

Defined a simple C function which tests two different algorithms (Ron Sheen's one and Randolph Franklin's pnpoly https://wrfranklin.org/Research/Short_Notes/pnpoly.html)

C code example:

int main(void)
{
int retval;
int num_sides = 5;
float lat = -36.10;
float lon = -70.00;

float x[] = {-35.90, -35.90, -36.30, -36.30, -35.90};
float y[] = {-70.20, -70.70, -70.70, -70.20, -70.20};

geom_area(&retval, num_sides, x, y, &lat, &lon);
printf("geom_area() reports:\t");
if (retval)
printf("Point inside\n");
else
printf("Point OUTSIDE!\n");

retval = pnpoly(num_sides, x, y, lat, lon);
printf("pnpoly() reports:\t");
if (retval)
printf("Point inside\n");
else
printf("Point OUTSIDE!\n");

exit(0);
}