SF TAC location

[kona...@bbkona.com]

When I have the Sectional centered over San Francisco and select the TAC a message appears to download the TAC. However if I move the the north edge of the SF Sectional I find the SF TAC available there.  It appears the location of the SF TAC is located incorrectly.

[Peter Gustafson]

Attached is a screenshot from my tile generation. It shows the TAC (with 50% opacity) overlaying the openstreetmap dataset.  Hence, the TAC is in the correct place.

The TAC goes to a base layer level of 11 (i.e., zoom level) whereas sectional goes to layer level 10.  The overall scaling changes between the two chart types. (a 2x change in pixels per linear mile)  If you are centered on current GPS position, it will line up appropriately when you switch.  If your not centered on the current GPS, it won't line up.  For example, you are 10 miles north of SFO (real position) and showing sectional centered on SFO, then switching to TAC it will show 2x = 20 miles from your current position (ie 10 miles south of SFO). Hence, it is appropriate to recenter to the current GPS after switching (to orient to the layers coordinate system) then move.  I'm not sure this is the optimal logic for the app from a users perspective, but it is the current logic.

On 4/30/19 10:36 PM, kona...@bbkona.com wrote:

When I have the Sectional centered over San Francisco and select the TAC a message appears to download the TAC. However if I move the the north edge of the SF Sectional I find the SF TAC available there.  It appears the location of the SF TAC is located incorrectly.

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[kona...@bbkona.com]

Thank you Peter for the excellent explanation.  I am in fact 100 mi south of SFO and doing flight planning so looking for/at the TAC for vfr routes etc.  Great that it works if I am, in fact, at SFO but confusing when using it from home for planning.

[Peter Gustafson]

Yes, I agree it can be a bit disconcerting.  I've found it is best to put the system in simulation mode and the place the aircraft at SFO (or whatever).  Start a plan at SFO and it will place the aircraft there (ie simulate the GPS position).  Subsequently switching back and forth among the charts is effortless.

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