[Talk-ca] [Imports] tiff, dwg and nad83

[Paul Norman]

Cc'ing talk-ca@ on this

> From: Frank Cox [mailto:theatre at melvilletheatre.com]
> Subject: [Imports] tiff, dwg and nad83
> 
> I live in a small city that is currently just a dot or blob on the
> OpenStreetMap. I discussed this matter with the guy at City Hall who is
> in charge of engineering, mapping and surveying and he stated that he
> would likely be willing to provide the data for our city so it can be
> added if I can find out exactly what you require and how to get it to
> you.

I'll link to http://wiki.openstreetmap.org/wiki/Import/Guidelines at the
start since it contains the guidelines.

> 
> He told me that his data is currently in Tiff and Autocad DWG files,
> tied to a GPS coordinate system called, I believe, NAD83. I wasn't smart
> enough at the time to write that number down at the time, but I'm pretty
> sure that's what he said.  He also said that he can convert his data
> into certain other formats, but he didn't specify exactly which ones.

NAD 83 is a coordinate system that differs slightly from WGS 84 which is the
standard for latitude and longitude. In North America the difference is
minuscule and you don't really have to worry about it.
 
> My current knowledge of this stuff is pretty much nil. My question is,
> what would it take to convert this data to a format that can be uploaded
> to OpenStreetMap? If it's something that would be quick and easy to do
> then he would probably do it himself. If it's an involved process, I
> told him that I might volunteer to do it myself if he will provide me
> with the data.

It's generally best if a local user converts and uploads the data. 

If they have tiffs and DWG files they likely have aerial photos (GeoTIFFs)
and geodata. The standard format for geodata from GIS departments is in a
shapefile (.shp) but it should be easy to convert between .dwg and .shp.

Both can be useful. City aerial photos tend to be more accurate than Bing
and frequently higher resolution. Geodata can sometimes be useful for
importing, but it takes some work to get it converted to .osm.

There are essentially two parts to the conversion, there's the conversion of
the geometry and the conversion to OSM tags. The first is easy, there's
several programs that will do it. The second requires looking at the
shapefile tags and converting them to OSM tags. Local knowledge helps here.
My preferred tool for converting is ogr2osm
(https://github.com/pnorman/ogr2osm).
http://wiki.openstreetmap.org/wiki/Import/Shapefile has a list of some other
programs.

You have to write a translation file for it. This requires knowing, for
example, that what the city calls a "Collector" road is what OSM calls
highway=tertiary. 

> The first step, and the reason why I'm here, is to find out exactly what
> would be involved in doing this, and then I can see about getting any
> required permissions from the City to use their data, and go from there.

Legally, the easiest would be if they provided the data on their website
under a license like PDDL. This is what some cities locally have done with
their open data initiatives.

If you get permission to upload it to OSM where it will be redistributed as
cc by-sa, ODbL or another open license as chosen in accordance with the OSM
contributor terms I believe that would be sufficient but the open data
advocate in me would prefer to see it under PDDL (or some other public
domain like license). For the photos you'd have to get permission to trace
them and then upload the works.

> I've been playing with computers for over 30 years but have never done
> anything at all with GPS stuff so it's all new to me. Therefore, an
> explanation starting from the basics would be greatly appreciated. If I
> do the conversion myself, all of my computers run Centos Linux.

Running linux is an advantage. Most of the instructions are for Ubuntu, but
you should be able to adapt them to Centos easily enough. The shapefile
conversion tools are easy to install. If you want to serve the geotiffs to
yourself there are a few options but it would be best to see how big they
are first. Geotiffs can range from a few gigabytes for a city to a few
hundred gigabytes. The techniques for hosting vary depending on the size.

Something else you might want to look at is
http://wiki.openstreetmap.org/wiki/CanVec. CanVec is best when it's used by
a local in combination with their area and it can save a lot of otherwise
tedious work.