GARS

[coudano]

So where is the discussion at these days on ditching CAP grids and just going to GARS?

[RogueLeader]

None that I've heard of. We still use them for our training and active missions.

[coudano]

I was just getting ready to teach a refresher on CAP Grid, and asking myself just...  why.

[Gunsotsu]

Because we should be using neither and switch to UTM.

[Eclipse]

Because we should be using neither and switch to UTM.

Absolutely, as well as compass' only in MRAD.

[RogueLeader]

Because we should be using neither and switch to UTM.

The Sherriff departments around here would be lost using utm.  Here in Wyoming, they control all Sar.

[sardak]

The CAP grid system and GARS are area reference systems. GARS by definition is not to be used for an area smaller than 5 min x 5 min. The CAP quarter grid, 123A, is even larger, 7.5 min x 7.5 min. Page 4-48 of the Land SAR Addendum to the National Search and Rescue Supplement states: GARS is a replacement for the sectional gridding so as to provide a current system that covers the United States with no overlapping names or coordinates. I've seen no effort on CAP's part to actually switch systems.

Lat/lon, UTM, MGRS and USNG are point reference systems.

Attached is the Geo-referencing Matrix from the Land SAR Addendum (with a non-existent footnote 10).

Mike

[coudano]

GARS by definition is not to be used for an area smaller than 5 min x 5 min.
The CAP quarter grid, 123A, is even larger, 7.5 min x 7.5 min.

Ok so maybe there is a little room for an argument there that I haven't considered before...

CAP quadrants are 7.5 minutes whereas a GARS quadrant is 15.

In terms of track spacing and track length, 7.5 seems like it may turn out to be more useful.  Certainly it is what we are more acclimated to.
Where I live that's
7.32ew x 8.7ns statute miles
approximately 63 square miles

So yeah the GARS quadrant is the size of the entire CAP grid, which would be double that in both length and width.
A keypad here is 4.87ew x 5.83ns miles
about 56 square miles for 2x keypads



So I mean, if you were going to assign an aircrew to 2x GARS keypads vice one CAP quadrant,
supposing that they were flying north/south, they would fly an extra 2.96 miles on each leg,

But their area would be 2.45 miles narrower from east to west, at half mile track spacing, that would be 5 fewer north/south legs.

You cover a bit less square mileage this way, but it seems like it actually gives you some more flexibility to really look where you want to look.

I don't imagine that we would reasonably assign a CAP airplane to search within a single keypad.  Although if you had a specific area you wanted a crew to look, they could get a keypad done REALLY fast.  I've been on searches where they're like "do the east half of this cap grid quadrant, and then leave"  Seems like that's pretty much same same?

meh

[RogueLeader]

That's why we have sub grids. We think that it's in the southern half, you give then the bottom subsections. You think it's in the southwestern corner of one grid or the southeastern corner of the next one, assign those subsections. It is a very flexible standard to use to effectively define the designated search area.

[coudano]

Sure, I mean GARS has subgrids too...

I did up this thing to show the difference between the two

Here (in red) is GARS 193LF
It gets divided into 4x 15' quadrants.  That's 193LF4 there in the bottom right (orange).
It is further divided into 9x 5' "keypads".  The center one (City of Warner Robins)would be called 193LF4kp5


Here is CAP conventional grid ATL382.  It's 15x15 and gets divided into 4 that are 7.5x7.5 as per usual
That quadrant (in blue) is kind of our typical air search area


Here are the two overlaying each-other