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# NAV1 CDI and GS Needle Offsets

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The FSUIPC5.15 Offsets Status documentation shows:

0C48 1 NAV1 Localiser Needle: –127 left to +127 right

0C49 1 NAV1 Glideslope Needle: –119 up to +119 down

2AAC 4 NAV1 course deviation needle (CDI), 32-bit float value, –127.0 left to +127.0 right

2AB0 4 NAV1 glideslope needle (GSI), 32-bit float value, –127.0 up to +127.0 down

Two questions regarding the above:

1. Are offsets 0C48 and 2AAC essentially the same except for the number format/precision?

and likewise

2. Are offsets 0C49 and 2AB0 essentially the same except for the number format/precision and the range specified in 2AB0 should be + - 119 as in 0C49 (i.e., the + - 127 in 2AB0 is a typo)?

I do realize full scale CDI deviation for a VOR signal is 4 times that for a localiser in terms of degrees, but I'm assuming the sim accounts for this and both full scale deviations will be represented by the + - 127 values.

Thanks,

Al

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Hi,

0x0C48 and 0x0C49 are each 1 Byte and so they are rounded values.  x02AAC and 0x2AB0 are float values (decimal precision).

But the max values are for 0x0C48/0x0C49  -118 to +119 and for 0x2AAC/0x2AB0  -119.0 to 119.0.

Quote

the same except for the number format/precision and the range specified in 2AB0 should be + - 119 as in 0C49 (i.e., the + - 127 in 2AB0 is a typo)?

If it is a typo then it is on MS / LM side, as both in their SDK describe those values with max values of -/+ 127 but both, MS and LM, give max values of -118/+ 119.

Thomas

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6 hours ago, Thomas Richter said:

But the max values are for 0x0C48/0x0C49  -118 to +119 and for 0x2AAC/0x2AB0  -119.0 to 119.0.

Hi Thomas,

Thanks for the reply. I do understand the numerical precision differences in the offsets, but I don't think the above quote is correct.

The P3D SDK shows the max values for both NAV CDI:index  and HSI CDI NEEDLE as  + - 127,

and for  both  NAV GSI:index  and  HSI GSI NEEDLE as + - 119.

So given numerical precision aside, I think there is a typo in the FSUIPC5 documentation for offset 2AB0 which is currently listed as

2AB0 4 NAV1 glideslope needle (GSI), 32-bit float value, –127.0 up to +127.0 down. According to the SDK the values should be + - 119.0.

In summary, the lateral needle range is + - 127, and the vertical needle range is + - 119.

Or else I'm really not understanding something.

Thx,

Al

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On 1/4/2020 at 3:49 PM, ark1320 said:

The P3D SDK shows the max values for both NAV CDI:index  and HSI CDI NEEDLE as  + - 127,

and for  both  NAV GSI:index  and  HSI GSI NEEDLE as + - 119.

Well, assuming the P3D SDK is correct, that is indeed the case. The pairs of offsets you refer to are obtained directly from the relevant SimConnect variables. Only the format is changed, nothing else.

The lower offsets (0C48 and 0C49) were originally derived in FS98 by hacking, and the range discovered by experiment. Nothing like the P3D SDK was available until SimConnect was invented in FSX. Documnetation inconsistencies may indeed therefore occur.  These are corrected as discovered, but this can't occur retrospectively -- it will be in the next full release.

So, thank you for pointing it out.

Pete

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