Robert West's plat (CE 585)

[Drew Phipps]

West's Plat:

The Dallas County Surveyor, Robert West, is a very interesting figure in the JFK assassination. First of all, he was actually present in Dealy Plaza during the assassination (southeast corner of Main and Houston). He testified as a State's witness in the trial of Clay Shaw. He heard four loud reports. He believed they came from the northwest quadrant of Dealy Plaza (which would be the grassy knoll area). He observed the motorcycle officers run up the grassy knoll. His most significant contribution however, is the famous plat he drew up at the request of the FBI, (WC Exhibit 585, Shaw exhibit 35).

(the following is from Herbert Blenner's site:

.)

The numerical data at the bottom is a little hard to read but it has been reproduced here on other threads. Here is a more legible image:



Here are the numbers on the shots:
Shot 1: 184 feet sight line, 171 feet horizontal.
Shot 2: 242 feet sight line, 232 feet horizontal.
Shot 3: 294 feet sight line, 285 feet horizontal.

You are all familiar with the Pythagorean equation, from which we ought to be able to determine the height of the shooter, given the above data. Since it is said that Oswald made all three shots from the same place, the height should be the same, allowing for elevation differences to the target, which Robert West has clearly marked for us. Being the official surveyor for Dallas County, I assume we can take those elevation figures as correct.

Height 1 = Shooter Height
Height 2 = Shooter Height + (423.07 - 419.07 = 4.0 feet)
Height 3 = Shooter Height + (423.07 - 416.83 = 6.2 feet)

However, the ever reliable Pythagoras gives us a different answer:

Height 1 = SQRT ( (184)^2 - (171)^2 ) = 68 feet
Height 2 = SQRT ( (242)^2 - (232)^2 ) = 68.8 feet (should be 68+4=72)
Height 3 = SQRT ( (294)^2 - (285)^2 ) = 72.2 feet (should be 68+6.2=74.2)

The math proves that the numbers on Robert West's survey are not only not accurate, they are not even internally consistent. Either the elevation figures are wrong, or the distances measured in the plat are wrong (or maybe both). Therefore, it is probably a mistake to base any conclusions (like whether SS Agent Jack Ready might have been in a position to block "Oswald's" view of JFK) on West's numbers.

[Chris Davidson]

Drew,

The shot labeled as#3:

I believe this is the direct correlation between CE875 and the SS/FBI plat of Feb64, dealing with the Altgens shot.

It appears the measurement was to the street, not JFK'S head on this plat. And, a 3degree slope was used in the calculation.

It would look like this:

Elevation 429.7 = TSBD at street
Plat élévation for last shot at 416.83
Difference = 12.87ft
TSBD window sill= 60.7ft
60.7ft + 12.87ft = 73.57ft
73.57squared x 285squared =294.34hypotenuse = plat entries for shot #3(Altgens)

The 3 degree slope = 5.238% grade = 1ft vertical/19.09ft horizontal ratio
Elevation change at shot#3 = 12.87ft
12.87 x 19.09 = 245.7ft

TSBD = Station# 2+50
2+50 + 245.7ft =Station# 4+95.7 = CE875

Attached is the "angle to horizon" from ground to rifle.

chris

[Drew Phipps]

If the numbers for shot three are correct, the other numbers are wrong. And it means that the FBI decided how far they wanted the shots to be and worked backwards from there to make it fit, ignoring West's actual measurements for shots 1 and 2.

[Chris Davidson]

Once again, measurement to the street, using a 3degree slope

Elevation 429.7 = TSBD at street
Plat élévation for shot at 418.35
Difference = 11.35ft
TSBD window sill= 60.7ft
60.7ft + 11.35ft = 72.05ft
72.05squared x 257.18squared =267.08hypotenuse = plat entries for elevation 418.35

The 3 degree slope = 5.238% grade = 1ft vertical/19.09ft horizontal ratio
Elevation change = 11.35ft
11.35 x 19.09 = 216.67ft

TSBD = Station# 2+50
2+50 + 216.67ft =Station# 4+66.67 = Tom Purvis' info obtained via Robert West.

chris

[Drew Phipps]

After time to think about your math, it seems to me that you are basing your figures on an assumption that Elm Street is a continuous 3 degrees slope from TSBD to point x. In fact Elm Street is level at the intersection of Elm and Houston and begins to slope down beginning at some point after you leave the intersection.


I think its far better to use the actual elevation changes measured by West, or by Robardeau in his map, than to imagine a perfect 3 degree slope from the base of the building to the street at point x.


Using those figures, I get an elevation change of (491.0 - 423.4) = 67.6 feet from nest to head (using the 53" measurement of JFK's head off the ground mentioned elsewhere in this forum). Measuring by Robardeau's plat map with pixel counting software (his scale is 4.14" per pixel) from nest to z313 (which incidentally matches a straight line between Nix and Zapruder, from the Nix photo at the headshot) you get a horizontal figure of 269.8 feet. The shot angle is (inv tan (67.6 / 269.8) ) or 14.1 degrees. The shot distance is SQRT((67.6)^2 + (269.8)^2) = 278.1 feet.

[Bob Prudhomme]

After time to think about your math, it seems to me that you are basing your figures on an assumption that Elm Street is a continuous 3 degrees slope from TSBD to point x. In fact Elm Street is level at the intersection of Elm and Houston and begins to slope down beginning at some point after you leave the intersection.


I think its far better to use the actual elevation changes measured by West, or by Robardeau in his map, than to imagine a perfect 3 degree slope from the base of the building to the street at point x.


Using those figures, I get an elevation change of (491.0 - 423.4) = 67.6 feet from nest to head (using the 53" measurement of JFK's head off the ground mentioned elsewhere in this forum). Measuring by Robardeau's plat map with pixel counting software (his scale is 4.14" per pixel) from nest to z313 (which incidentally matches a straight line between Nix and Zapruder, from the Nix photo at the headshot) you get a horizontal figure of 269.8 feet. The shot angle is (inv tan (67.6 / 269.8) ) or 14.1 degrees. The shot distance is SQRT((67.6)^2 + (269.8)^2) = 278.1 feet.

Hi Drew

I believe the actual average slope of the entirety of Elm St., to the Triple Underpass, is 3.13°, and you are correct, in that Elm St. is somewhat level in front of the entrance to the TSBD. However, this only makes the remainder of Elm St. that much steeper.

You are correct in surmising that the only thing that can be trusted are the elevation changes as determined by Robert West.

I have been a bit busy, as of late, and have only had a little time to work on my wooden "model" of Dealey Plaza. I had planned to simply have my Elm St. descend at a steady 3.13°, but this discussion has prompted me to go the extra distance, and use West's elevations to make it more accurate.

It is more difficult to precisely locate the shots, so I will simply have an area marked out from the Stemmons sign to the concrete steps, and use the entire section between the two sites to determine if JFK was at any time visible from the Sniper's Nest.

[Chris Davidson]

Drew

WC Street Elevation at extant Z313=418.48

SS/FBI Street Elevation at extant Z313=418.35

The 3 degree slope works with the existing entries on the SS/FBI plat starting at Station# 2+50 / Elevation 429.7

I would suggest you calculate what the Elm St slope is with your shot distance of SQRT((67.6)^2 + (269.8)^2) = 278.1 feet.

chris