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[mkgmap-dev] Improved street search in index branch

From Johann Gail johann.gail at gmx.de on Wed Jan 19 20:24:02 GMT 2011

Steve Ratcliffe schrieb:
> Hi
>> I had some looks at the code, especially on MDRSection7, which is
>> important for street search. And, yes, there are some more fields
>> decoded. But most of the comments are in polish, so it's very hard (at
>> least for me) to unterstand what those fields are used for and where to
>> get the required data.
> There are other possible fields but they are not necessarily essential
> as mapsource adds some of these fields when it downloads to a device,
> so they do not need to be present in the index to begin with.
Correct, I think we should get basic search working first. But my final 
destination would be a working search on the devices without downloading 
from mapsource. I would be very happy, if we get so far.
> As far as I understand it, one of these fields is a flag to say that
> there is more than one word in the name of the street (or perhaps a
> count).
The xflag seems to be a count of some sort. The count could become 
greater then 256 and then it will be splitted to two bytes. Or are this 
the accented characters with an ascii code > 256? I don't think so. Also 
I think this is optional and not needed for basic working.
> Another field is used for an alternative kind of index where every
> word in the street name is indexed separately.  So if you had a name:
> 	Yellow Grass Lane
> it would be sorted under 'Y' as normal, but also under 'G'.  The entry
> that was under 'G' would have this field set to the position of the
> character 'G' in the name - so 8 in this case (or 7 if it starts at 0
> - whatever).
> While this would be useful, we need to get the basic index working first.
> It would be good to know exactly what is required to get things
> working on the device, since the index has very many possible
> sections and we don't have enough people working on it to implement
> everything.
> My next guess would be mdr 20, 21, 22 as these are referred to in the
> reverse index which is used by mapsource to determine what is
> downloaded to the device.  They are lists of pointers into the street
> names ordered in particular ways (city, region etc) and so very
> relevant to the problem areas.
> ..Steve
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