I can not help you about Bitmaps, I have only been looking into the alerts in poi.
Its been a wile since I looked into it, and have many unsorted papers .
I have a picture here of Hex, dont know if it helps you.
This is only what i experience, and I my be wrong and my memory could be failing.:
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A blue line divide the picture in 3 parts: Header-poi nr1-poi nr2
Blue :coordinates
Yellow: Text
2 byte,Inside Red line/white:Proximity
2 byte,Inside Green line/white:Speed
1 byte,Inside Blue line/white :Alert on(01), of (00)
1 byte, black line/white: Type of alert (00 360° alert)(01 Along road)(02 TourGuide) This file is manupulated and shows 04.
1 byte ,dark blue line/white: Custom sound nr/ if no custom sound: 00=Beep/01 Tone/02 3 beep/03 silence/04 Plung/05 dobbel plung.
Alert part in poi start with: 03 00 00 00 0c
Blue line/Pink: Offset of the code, and the code.(this is an PoiLoader file, so its not coded, just to show)
Brown: Length of text (how many byte)
ligh blue: language
This is what I can recall at the moment.
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