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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.

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Calculate Camera parameters and HandEyeCalibration

I'm trying to port an old Augmented Reality project, which is based on the metaio framework for an other see-through HMD. Cause metaio is bought by apple, it's available documentation and support is very limited and this new HMD is not supported out…
user2479595
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Transforming coordinates of feature in openlayers

I want to transform the coordinates for an entire feature in openlayers. I have had success using ol.proj.transform to transform a single coordinate to a different projection, but is there any function that you can feed an entire feature, and all…
Stephen Fricke
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Adding a projection to an NHibernate criteria stops it from performing default entity selection

I'm writing an NHibernate criteria that selects data supporting paging. I'm using the COUNT(*) OVER() expression from SQL Server 2005(+) to get hold of the total number of available rows, as suggested by Ayende Rahien. I need that number to be able…
Sandor Drieënhuizen
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How to use NHibernate Projections to retrieve a collection

I am lazy loading the collections, and also because there are so many fields within the person table, I am writing a projection function to retrieve only certain properties. It works with properties, just not collections of other entities. I would…
luke
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How to convert NAD 83 coordinates to latitude and longitude with rgdal package?

I have coordinates, all of which should be located in DC, but I cannot figure out how to convert them from NAD 83 to latitude and longitude in R. I'm using the spTransform() function in the rgdal package and get an error about non-conformant…
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Are path-dependent types type projections?

I'm reading Scala in depth now. Here is an excerpt from the book: All path-dependent types are type projections. A path-dependent type foo.Bar is rewritten as foo.type#Bar by the compiler... In Scala, all type references can be written as…
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Datashader integration for polygons in plotly mapbox

I'm using plotly's Scattermapbox to overlay a map with a shaded image of polygons created by datashader's shade function (based on https://plotly.com/python/datashader/), but the projections do not seem to align, see picture below. Any suggestions…
Manuel Diehn
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Projection Problem in Kalman Filter for Navigation

I am currently working on a simple and small Kalman-Filter for GPS-Navigation. I am getting from my GPS-Sensor the current location, course angle and speed. So the Kalman-Filter should fuse the current measurement and the linear movement beginning…
thomas
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Spring Data Projection with OneToMany returns too many results

I have a JPA entity (Person) with onetomany relation (ContactInfo). @Entity public class Person { @Id @GeneratedValue private Integer id; private String name; private String lastname; private String sshKey; …
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nhibernate queryOver projection syntax

I am trying some code out from a NH 3.0 Cookbook, and wondering why I can't get the code below to compile. I think the QueryProjectionBuilder that should make this work is in "NHibernate.Criterion.Lambda" but the using directive for it doesn't…
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Event sourcing: denormalizing relationships in projections

I'm working on a CQRS/ES architecture. We run multiple asynchronous projections into the read stores in parallel because some projections might be much slower than others and we want to stay more in sync with the write side for the faster…
urbanhusky
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Improve performance of event sourcing projections to RDBMS (SQL) via .NET

I'm currently working on a prototype in C# that utilises CQRS and event sourcing and I've hit a performance bottleneck in my projections to an SQL database. My first prototype was built with Entity Framework 6, code first. This choice was made…
urbanhusky
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Projecting a 3D point to 2D screen space using a perspective camera matrix

I am attempting to project a series of 3D points onto the screen using a perspective camera matrix. I do not have world space (or consider it being an identity matrix) and my camera does not have camera space (or consider it an identity matrix), I…
Gary Paluk
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Simplifying D3js' SVG path generated string

I am trying to optimize a little bit the SVG I am generating using the amazing D3js geo module. I am using d3.geo.path as the d attribute generator for SVG paths: path = d3.geo.path().projection(config.projection); // projection is initialized…
Óscar Gómez Alcañiz
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How can I use ffmpeg to change 360 video projection?

I want to convert 360 videos from equirectangular to cubic projection. How can I do this with ffmpeg? What are other efficient open source approaches?
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