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89
votes
8answers
17k views
What's the difference between a projection and a datum?
What's the difference between a projection and a datum?
1
vote
1answer
32 views
Do transfer edges add to the distance cost of a route?
Transfer edges are commonly used in a network dataset to carry a time cost in one direction only (either to-from or from-to). This is fine if the impedance used is time, i.e. find the route that will ...
50
votes
12answers
12k views
Concave Hull: Definition, Algorithms and Practical Solutions
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 ...
5
votes
1answer
73 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 ...
2
votes
0answers
68 views
Linear Referencing Methods: Station Equation origins
I am working in the pipelines field, and I get in touch with the concept of the linear referencing methods, specifically with station equation method.
I had to do research about this method, I'm ...
8
votes
4answers
94 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 ...
11
votes
3answers
267 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 ...
6
votes
1answer
95 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 ...
3
votes
0answers
182 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 ...
8
votes
3answers
147 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 ...
9
votes
3answers
313 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.
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3
votes
2answers
544 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 ...
12
votes
5answers
1k 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. ...
