Redesign first byte in twkb

[nicklasaven]

Now in spec the first byte in twkb is used like this:
bit 1: Is ID included in twkb?
bit 2-4: serialization method
bit 5-8: precision, number of decimals in coordinates

I don't think the possibility to use different serialization methods will ever be used. I think the varInt method will be the one and only. So, for that reason I think those bits instead should be used for optional features, the same way as the ID? bit.
The other 2 optional features I can think of is:

1. size of geometry as discussed in Add size of twkb #7
2. bounding box of geometry

If totally leaving the idea of different serialization methods we still have one bit left for future optional features.

Then comes the order of those 3 bits with optional features.

Now the ID? bit is the first bit.
I think it wold make sense to have the order

1. size?
2. bbox?
3. id?
4. unused bit
   5-8) precision, number of decimals.
   because that is the order they would apear later on in the geometry for practical resons.

But I don't know if there is any implementation out there that will break if moving the ID-bit.
I don't think any implementation of twkb is released yet so I guess this is still the right time to changing the design of the initial byte.

[nicklasaven]

Ok, it's in spec, implemented in PostGIS trunk and in twkb.js