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31k views

What's the difference between a projection and a datum?

What's the difference between a projection and a datum?
20k views

What are Definition, Algorithms and Practical Solutions for Concave Hull?

Convex Hull A convex hull of a shape is defined as: In mathematics, the convex hull or convex envelope for a set of points X in a real vector space V is the minimal convex set containing X ...
3k views

Algorithms for matching segments

What are the best algorithms to match segments? I'm trying to match corresponding segments from two map sources, one less accurate but with segment names, and one more accurate without segment names. ...
330 views

Does Earth's magnetic field affect any datum definition?

I had an interview last week. One very interesting question was "does earth's magnetic field affect any datum definition?" I was sure it does not for geocentric datums. But I thought maybe the ...
355 views

How can Flocking Algorithms be used in GIS?

The first flocking algorithm was written by Craig Reynolds in 1986. A recent browser implementation can be found here. ...
128 views

Selected Literature on coordinate transformations?

I am looking to hone my skills in the theory and the mathematicas involving the projections systems, projection transformations ( from xy to uv, φλ and vice versa). Can you share the ...
167 views

Location storage and query algorithms. How do they work?

One of the most important aspects of a GIS-equipped database is that it provides the user with the capability to quickly query for all points within some arbitrary geographic area that match some ...
112 views

How can I generate a range of pantones for a map?

When I am given a map (or make one...) I often like to get an idea of the range of colours present. One thing this does is it allows me to quickly visualize contrast (helps build maps for colour blind ...
321 views

Terminology problem - Raster vs Grid vs Lattice

I have a question about GIS terminology - what is the difference between grid and raster and grid and lattice - in theory?? I thought, that raster is regular network and value is in the cell and the ...
177 views

How to store route names of a stop belonging to multiple routes

I've been reading the ArcGIS help files on route analysis to gather more information on what attributes are stored with Stops. Maybe I've stared at the screen too long, but I cannot seem to understand ...
1k views

Is the Fourth Dimension used in GIS?

Whilst working with OGR, I came across the following field used define a geographic dataset: COORD_DIMENSION The spatial dimension (2, 3 or 4 dimensional) of the column. Whilst I've used 2D and 3D ...
244 views

Topology - To be, or not to be, that is the question [closed]

Topology, I mean "real" topology, is not a new concept and it's available since a long time in GRASS gis. I won't speculate the reasons myself but, after a long period of spaghetti model ...
233 views

Linear Referencing Methods: Station Equation origins

DEAR PEOPLE FROM THE FUTURE: Here's what we've figured out so far… I am working in the pipelines field, and I get in touch with the concept of the linear referencing methods, specifically with ...