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Questions tagged [projection]

A projection is the transformation of a set of data from one form into another.

Mathematically speaking a projection is a function that yields the same result if applied multiple times.

The term is used with this meaning in graphics when 'projecting' a 3D scene on a 2D canvas.

The same is often happening when analyzing data with many dimensions (age, gender, number of transactions, ...) and projecting it on fewer dimensions, in the simple case by just dropping dimensions or by creating new dimensions like (might commit fraud).

When dealing with typed languages the dimensions might be attributes of a class. So if I have one or multiple types with attributes (A, B, C, ...) and create from instances of those types instances of a type which has only the attributes (A, B) this is a projection too.

Another example are databases. A projection is an operation which discards some attributes of a tuple, in other words, which omits some columns of a relational database query result. For an object or document database a projection filters out some fields.

After all a database projection yields the same result if applied multiple times, too.

2017 questions
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Project Scipy Voronoi diagram from 3d to 2d

I am trying to find a way to calculate a 2d Power Diagram in Python. For this I want to make use of the fact that a 2d power diagram can be interpreted as the intersection of a regular 3d voronoi diagram with a plane. With the SciPy Voronoi module I…
yellowcap
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how do I re-project points in a camera - projector system (after calibration)

i have seen many blog entries and videos and source coude on the internet about how to carry out camera + projector calibration using openCV, in order to produce the camera.yml, projector.yml and projectorExtrinsics.yml files. I have yet to see…
nass
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Does type projection have an opposite, or is it still projection (or just mapping)?

This is based on my assumption that taking an object of type: public class Fruit : IBasicFruit, IFruitDetails { // IBasicFruit implementation public string name { get; set; } public string color { get; set; } // IFruitDetails…
Jay
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OpenLayers Google Maps Projection Problem w/ KML

This is my first time on stackoverflow and working with Openlayers & Google Maps. I've been browsing different forums & sites, including OpenLayers.org, to solve my issue. I've done searches on a combination of the following: openlayers, google map…
Tiffany
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Hibernate: Projection of a collection returns ArrayIndexOutOfBoundsException

I'm trying to get a partial object back using projection in hibernate, like this: Movie class: @Table(name = "Movies") public class Movie extends Entity { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Column(name = "id") private Long…
TimDMeyer
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How to modify only one or two field(s) in LINQ projections?

I have this LINQ query: List customers = customerManager.GetCustomers(); return customers.Select(i => new Customer { FullName = i.FullName, Birthday = i.Birthday, Score = i.Score, // Here, I've got more fields to fill …
Mehdi Emrani
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AutoMapper complex nested mappings

I've read this example on AutoMapper's GitHub, but the example assumes there'll only be one way to map InnerSource, ever: Mapper.CreateMap(); Mapper.CreateMap
Carson Myers
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back-projecting a 2D point to 3D Plucker line

I'm trying to build a tracker (hand tracking personal project), and for this reason I need to back-project a 2d point to a 3d line, using Plucker coordinates. (like ray tracing) As an input, I have the 2d coordinates of a point and the projection…
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Get Longitude Laltitude of a point in my Worldmap in Mollweide projection

I searched about a day now, but didnt find any example for my problem in Javacode. I have a worldmap with a size of 2000*1400 Pixels with a 'Mollweide' projection. How can I find out what is the longitude and laltitude of the point (500,300) in my…
mcfly soft
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Given an array of records, how can I get an array representing a field from each one?

I have to translate some Fortran 90 code and found an interesting language feature. As an example, they define the following type and dynamic-array variable: TYPE WallInfo CHARACTER(len=40) :: Name REAL :: Azimuth REAL …
bruce
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Projection on a MongoDb Query using Spring data and QueryDSL

I have a Spring MVC/Spring Data / Mongo DB application. I have setted up my environement according the the spring data documentation and my repositories work fine (I can execute queries with predicates) I was wondering if it was possible to execute…
ufasoli
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Hibernate Projections List

I ned to get only a few column values from the table. So I have used Projections to achieve this. The code works, but I don't think it is effective. My issue was when I used ProjectionsList & then set the criteria.list to an ArrayList - the…
Harry
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Check polygon intersection in R: sf::intersects incorrectly returns TRUE result while rgeos::gIntersects correctly returns FALSE

I'm trying to check whether two polygons intersect in R. When plotting, they clearly do not. When checking the intersection, rgeos::gIntersects() currently returns FALSE, while sf::intersects() returns TRUE. I imagine this is due to the polygons…
Rob Marty
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Using a projection from the elements instead of a comparator for sorting

I searched for c++ analog for this (python): sorted(vector, key=lambda x : my_function(x)) There is of course the construction: std::sort(vector.begin(), vector.end(), [](const auto& lhs, const auto& rhs) { return my_function(lhs) <…
MrNewman
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3D Projection Issue: Z Value doesn't lie in [1,-1] after Perspective Divide

I'm trying to do a simple perspective projection in the process of rasterizing a 3D point. Here are all the matrices and other info. All Matrices are row major. The coordinate system is Right Handed. The Camera is at [0,0,-1] and the point is at…
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