[mkgmap-dev] open issues in the housenumber2 branch

Sun Mar 1 10:44:53 GMT 2015

Gerd, 

Thanks for the explanation, and sorry if I missed it before. 

So we have two extremes: on the one hand accuracy which would best be
served by having individual addresses in the output; on the other hand
we have efficiency (storage and lookup performance?) which would call
for "interpolation ways" as long as possible. I guess Garmin assumes the
intermediate numbers in such a way are equally spaced. Combining a set
of individual address nodes for e.g. 1,3,5,7,9 into a single segment
will lose the exact placement of {3,5,7}. In practice I guess the
inaccuracy will only be a matter of a few metres, so acceptable for most
purposes. 

Maybe we could have two modes: accuracy mode, where individual addresses
are mapped to individual Garmin address nodes (but interpolation ways
could stay as they are, but split at any explicit intermediate nodes
with an address) and small mode, where an attempt is made to match the
individual addresses into ranges, corresponding to the routable way
segments which stay as they are? In the first case the road segments get
chopped up by the address information, in the second case the address
information is made to fit the road segments. 

If we are to decide between these two approaches on a per segment basis,
could we look at the results given by the second approach (consolidating
individual addresses into a range) and examine the positional error with
any intermediate explicit address nodes? If the error is less than, say,
10m, then we can accept the consolidated range, and otherwise consider
splitting at the address with the largest positional error and
re-assessing? 

Take a road segment and find the numbers in OSM closest to the end
points on each side of the road. Interpolate between the end points. For
each intermediate address, if OSM has an explicit location AND this is
more than 10m from the interpolated location: complete the scan to find
the biggest such error, split the segment there and recurse. 

Colin 

On 2015-03-01 11:02, Gerd Petermann wrote: 

> Hi Colin,
> 
> I think I tried it already, but here is my current knowledge:
> The Garmin format stores addresses like interpolation ways along roads (=routable ways)
> The corresponding information in mkgmap is stored in class Numbers,
> which has the fields start, end, and style, once for the left, once for the right side of the road.
> The style tells you what numbers are between start and end, one of "odd,even,both,none".
> The log shows this as e.g. (n4),B,183,194,B,174,182
> which means something like
> "road segment number 4 has B="both" numbers from 183 to 194 on the left and B="both" numbers from 174 to 182 on the right"
> 
> Another example: (n3),O,1587,1587,E,764,894 
> means
> "road segment number 3 has O="odd" number 1587 on the left and E="even" numbers from 764 to 894 on the right"
> The special case (n4),N,0,0,N,0,0 means "no numbers in road segment 4"
> 
> As you can see we can describe single numbers as well as intervals. 
> The numbers for the whole road is stored as a list of the above intervals, starting with the first segment.
> This looks like
> 0,N,0,0,B,782,219 + (n1),B,240,1119,B,300,1161 + (n2),...
> 
> The tricky part:
> Where does a segment start and end?
> Each (number) segment starts and ends with a so called number node.
> Each crossing or road junction is always a number node, any other point on the way can be flagged as a number node.
> 
> When you search for an addresss using a street name and house number,
> the Garmin software seems to check each possible road starting with the first segment.
> If the number falls into one of the segments (and matches the odd/even criteria)
> the corresponding position in that road segment is interpolated and shown as a result,
> else the closest matches are shown.
> 
> My goal is to produce a reasonable list of segments so that the interpolated 
> positions are close to the point on the road which you would like to use to 
> "park your car" without blowing up the img size too much and without
> adding number nodes that cause visible angles (zig-zagging).
> 
> Gerd
> 
> -------------------------
> Date: Sun, 1 Mar 2015 10:31:03 +0100
> From: colin.smale at xs4all.nl
> To: mkgmap-dev at lists.mkgmap.org.uk
> Subject: Re: [mkgmap-dev] open issues in the housenumber2 branch
> 
> Gerd, can you explain how addresses are stored in the Garmin maps? Are they millions of individual nodes, or "interpolation ways" with a start and an end? Are they just coordinates, or are they internally linked to a road in some way? Can it handle non-numeric house numbers? Understanding the "target data model" might help to assess all the possibilities we have in interpreting the data from OSM.
> Colin
> 
> On 2015-03-01 09:42, Gerd Petermann wrote:
> 
>> Hi all,
>> 
>> during the last days I've analysed the reasons for the error messages reported
>> by some of you. I came to the conclusion that I have to 
>> - change the handling of addr:interpolation ways completely
>> - add code to detect the "random number" case earlier and - if detected - 
>> use different methods to split the number intervals
>> 
>> Both are rather complex changes, so I'll need a few days to code this.
>> 
>> One open question for you:
>> How should we handle "missing" information?
>> If mkgmap finds the numbers 1,3,9,11,17 in that order on the left side
>> of a road called ABC, it can create different housenumber informations.
>> One could be like "odd numbers from 1 to 17 on the left",
>> another could be a more complex sequence 
>> 1) "odd numbers from 1 to 3 on the left",
>> 2)"odd numbers from 9 to 11 on the left",
>> 3) "odd number 17 on the left"
>> A search for ABC 5 would either show a point between 3 and 9
>> or two entries with the numbers 3 and 9.
>> The latter tells you that OSM probably doesn't contain the 
>> exact information and let's you decide where to search for ABC 5.
>> 
>> The trunk version tends to the simple info, while r3486 
>> is more likely to produce the complex one.
>> I think trunk is better here, the complex case should only
>> occur if the "random number" case was detected.
>> 
>> Do you agree?
>> 
>> Gerd
>> 
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>> mkgmap-dev at lists.mkgmap.org.uk
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