[GIS] How to calculate distances between addresses and cities and coast line

distancefile-geodatabaseopen-source-gisvector

I am totally new to GIS, and so I apologize if my question is not clear enough. My basic problem is the following:

I have about 160,000 Danish addresses with longitude and latitude for each address.
I would like to calculate the distance to the nearest big city (preferably by road and not straight line), and the distance to the coast.
I have access to a topographical map of the roads and cities in Denmark in the scale of 1:1000000.
The data structure is vector.
The format is GDB (ArcGIS).
The coordinate system is UTM32-ETRS89.
I use windows 7 64 bit.

I have the following question:

Is there a free GIS to work with the GDB format (and preferably a reference to a tutorial or similar for absolute beginners)?

Any comments are welcome, and I gladly provide more info if needed.

Thanks a lot!!

Best Answer

A good place to start with FOSS4G is QGIS. I reccomend that you use the OSGEO4W installer because, with that, you can ensure you have the file-based GDB capability installed, which you appear to need.

QGIS has a RoadGraph plugin which,you can install by opening QGIS and going Plugins->Manage and Install Plugins and then locate it in the Get More section. Here is a how to on using the RoadGraph plugin for calculating shortest distance.

However, there are other solutions which may be more powerful. One is PgRouting. It would require you to upload your file-based GDBs to a PostGIS database.

Anyway, this should give you something to get started and all the software listed here is free.

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[GIS] How to calculate orientation of line segments using open source GIS

To get an angle from a line you just need to find the angle of the normalized direction. The Atan2 function is available on every computing platform I have used, even calculators. The basic idea is to get a normalized vector for the direction of that line then get the angle.

var normal = line.Direction.GetNormalized();

For your case since you need it to be north (+y hopefully) relative and possibly clockwise you could reverse the inputs to Atan2 like so:

var radians = Atan2(normal.x,normal.y);

And if you need counter-clockwise negate the result of Atan2. For degrees just multiply by 180 then divide by PI. Also note that when the result is negative you can add 2*PI.

if(radians < 0) { radians += 6.28... }

Edited: to correct an error for counter-clockwise.

Note: only works if North is always up.

[GIS] Calculate distances between series of points in postgis

Hallo

If assume that you have an id field called gid and that the first point has gid 1 then you can do something like:

ALTER table my_table ADD COLUMN dist DOUBLE PRECISION;

UPDATE my_table SET dist=ST_Distance(my_table.geom, b.geom) 
FROM (SELECT geom FROM my_table WHERE gid = 1) b;

That will add a column called dist and fill that column with the distance to the point with gid=1

HTH Nicklas

Best Answer

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