Constructing Satnav Maps

[jad12]

Apologies if this is a repeat post. I thought I had submitted and had gone through last Friday but now I don't see it.

I have made this a new post as the years have clocked on since the articles.
I'm looking for more insight as to how maps are constructed, routing mechanics and the database of attributes. Is there any updated info?

The basics I have: A georeferenced raster layer as the very base to give a map look or, perhaps more likely, a digitised polygon vector layer to more appropriately visually represent different road types, eg one way streets. A road segment line vector on which routing is performed. I have the A star algorithm but expect it to be more involved, as Tom Tom IQ Route suggests. Perhaps the polygon layer is also included in the mechanics eg to allow for one way systems.

I expect organisations have their own ways but in general what makes the map look a map, whether from start or updating? Do they tediously digitise or rely more on satellite or aerial imagery? I guess I'm asking how does Cartopia work.

As with a lot of other mapping the satnav specs do not give much detail on the map. What coordinate system and datum? Like Google Earth are they WGS84 the GPS system, or local as would be if base maps are from mapping agencies? In the UK I assume much of the base mapping was from Ordnance Survey, OSGB coordinate system. Is this used and WGS84 datum shifted to OSGB or is OSGB shifted to WGS84? The difference is about 100m at Greenwhich varying over the country. Along with this are map vertices/nodes in lat and long or grid?

Lastly, for now, what sort of database deals with all the intricate attributes, names, POIs in a small box that I guess has limited software and storage capability.

Grateful for any pointers to info. Sorry it's looong. Much to learn.

[DennisN]

Yes it IS a repeat post. Your previous one was removed because it was sent from a recognised prolific spam IP.

Can you give any explanation for that and an argument for us not to ban you from this site?
_________________
Dennis

If it tastes good - it's fattening.

Two of them are obesiting!!

[jad12]

Hi Dennis

So I am not going mad. It looked there then it went.

Simple answer to both questions is, no, I have no idea.

Not sure about the will in your signature, but I'm a bit tired and confused after the wake. In Vietnam its the 'happy die day' anniversary of a family member.

If you allow, give me chance to be less t&c later, I'm UTC+7 and tired out.

Can I give my reasons in writing tomorrow. I can then make my explanations, as guesses to what and why. For, I really do not know.

End of day it is your decision.

[jad12]

Concerning my last I believe a quick response was appropriate.

Can you give me the spam IP, maybe I can investigate although there is much computer security that is beyond me.

I am in Vietnam running a VPN which mostly connects to Hong Kong, but typical other connects are Singapore, California and Holland. How it bounces around from the indicated connection I do not know. Vietnam is not I believe a prominent spam source but along with extra security I thought VPNs were somehow meant to avoid potential spam sources.

I would have hoped that the content of my post asking for more insight would have shown my sincerity and that also I am proficient enough in GPS, mapping and navigation to contribute to the forum.

This is an explanation of possibilities but I cannot provide any proof. I can only await your decision and hope for the best.

Finally this is an internet concern not Satnav but if there is any advice available to avoid this situation I would be grateful.

Many thanks and cheers.

[MaFt]

Hi Jad,

Thanks for the confirmation of VPN - that explains the IP address issue that DennisN picked up on. Sadly we do get spam posts so we have to be vigilant.


Anyway, onto your question. Exactly how they make the maps would, I assume, be a bit of a trade secret with the map providers.

To be honest I've never seen *anything* about exactly ho they get their base maps etc but I know a few years back Mike (one of the directors) had a day in TeleAtlas's (now TomTom) mapping van here: http://www.pocketgpsworld.com/teleatlas-mapping-van-a1000.php

And wow, that was 10 years ago - a bit more than a few!!

[jad12]

First my apologies, I have been a bit disassociated over the last few weeks. One reason was trying to delve into VPNs - I fear I am none the wiser.

Anyhow, many thanks for this pointer. It was useful as it summarises what I think I know to date.

I still have some curiosities. I bet the answer will be 'no' but I will ask.

It has been some time since I looked at a satnav in detail. Do they nowadays give any map info in the manual specs? This is stuff that is immaterial to the practical use but stuff I think should be there. Things like what is the coordinate system? This includes projection, spheroid and datum (all also lacking in many other maps).

For the UK ok its going to be OSGB based but not necessarily OSGB coord system. GPS works on WGS84 and sums in the box will have to convert to OSGB. Or, OSGB map is shifted to WGS84. The end practical result is it puts us in the right place but the location, grid or lat/long will differ.

Another horror for me. Without local knowledge a map without scale is a broken pencil - pointless. Any chance nowadays?

Many thanks and cheers
Jad

[jad12]

In addition. Just had a thought -- I am slow.

Do modern units give a lat/long readout of position? The ones I have seen, in Vietnam taxis, do not. But maybe this is something in settings that would not be selected here as the concept is beyond most Vietnamese, as well as reading a map.

Plotting this on say an OSGB paper map would give an indication. Does the position put you where you can see you are?

Cheers

[M8TJT]

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