MongoDB projection means to select only the necessary data instead of selecting the entire data for a file. If a document has 5 fields, you need to display only 3, and then select only 3 fields.Find () methodMongoDB's Find () method, which is interpreted in the MongoDB query document, accepts the second optional parameter that is the list of fields to retrieve. I
Tags: http io os ar sp file data on CTIMongoDB projection means to select only the necessary data instead of selecting the entire data for a file. If a document has 5 fields, you need to display only 3, and then select only 3 fields.Find () methodMongoDB's Find () method, which is interpreted in the MongoDB query document, accepts the second optional parameter that is the list of fields to retrieve. In
Tags: operator haha emma _id Comm MONGO add reason DirectA simple projectionA little use of mongodb know that the projection is very simple, directlydb.student.find({_id:ObjectId(‘5a5085aed8f10c1a6cc0395b‘)},{comments: 1})Add a $slice projectionHowever, when I want to give comments ( $slice ) How to do it?The wrong approachThe following are the wrong practicesdb.student.find({_id:ObjectId(‘5a5085aed8f10c1a6
Map Projection ( Map Projection )Http://baike.baidu.com/view/94066.htmConcept:Map projection is the theory and method of converting any point on the Earth's surface to a map plane using certain mathematical laws.Since the earth is an irregular pear-shaped sphere that is slightly flattened at the equator, its surface is a non-flattened surface, so the use of any m
1. Gauss-gram Gauss–krüger projectionGauss-gram Gauss–krüger projection This projection is by the German mathematician, physicist, astronomer Gauss in the 1820s, after the German geodesy home Crugge in 1912 to complement the projection formula, it is called Gauss-gram Gauss–krüger projection. Also known as transverse M
This article is the derivation of the http://www.codeguru.com/cpp/misc/misc/math/article.php/c10123__1/ Deriving-projection-matrices.htm, due to my limited ability, there is no understanding of the translation of the place you can refer to the original, thank you ^-^!A star on a meteorIf you want to reprint, please indicate the source, thank you!In the basic matrix transformation of 3D graphics program, the projec
4. Map projection4.1 Projection EssenceA method of mapping points on the Earth's ellipsoid to a plane, called a map projection .Why do you want to project?– Geographical coordinates are spherical coordinates, which are not convenient for acreage of parameters such as distance, azimuth and area.– The Earth ellipsoid is a non-developable surface.– The map is planar, meets visual psychology, and is easy to dis
(2) Parallel projection"The projection of the sun's rays is a parallel projection."If you move the center of the perspective projection to Infinity, each projection line becomes a straight line that is parallel to each other , and this p
Gaussian-kruger projection and UTM projection are both variants of the horizontal mocator projection, at present, some foreign software or the supporting software of imported foreign instruments often do not support Gaussian-gram projection, but support UTM projection. There
ellipsoid model (XI ' an 80) is most accurate in the Chinese region, its geometric center is certainly not the centroid of the Earth, but elsewhere. So this geometric center is called the Reference Center, referred to as the heart.On the earth a point latitude and longitude, is based on the reference ellipsoid to calculate, so, the same place, with Beijing 54, Xi ' an 80,wgs84 calculated longitude and latitude is three different values. Since GPS is WGS84, we see the latitude and longitude of t
ext.: http://www.cnblogs.com/graphics/archive/2012/07/25/2582119.html
Overview
The projection transformation is to show how to display the three-dimensional model to the two-dimensional viewport, which is a three-dimensional to two-dimensional process. You can consider a projection transformation as the focal length of the camera, which simulates the process of selecting a lens for a camera. A
The previous modelview transformation is equivalent to placing the camera and adjusting the position and angle of the object to be photographed. The projection transformation corresponds to adjusting the camera lens distance to obtain the scene.
BelowCodeSet the current matrix mode to projection matrix:
Gl. glmatrixmode (gl_projection);
Subsequent coordinate transformations are for the
In the introduction to world projection, we mentioned mocato projection, which isBy HollandCartographyG. Mercator was created in 1569. Currently, most popular map websites such as Google map and Baidu map all use this projection (Web mocato projection). Today we will briefly introduce this
§ 6 projection of vectors on the axis (projection)
IAngle between two vectors of space:
There are two vectors that are handed over to the point (if they are not intersecting, one of the vectors can be translated to make them cross), and one of the vectors is rotated inside the plane determined by the two vectors, so that the square direction of it overlaps with the square direction of another constant, so
The projection operation of the Hiberante object mode and the projection of the SQL statement (the hibernate usage of the aggregation function)Recently used hibernate projection, write a diary to record.(⊙o⊙) ... Prerequisites: Paired with Hibernate environment. MyClass refers to an entity class that has been mapped wellThe following 3 functions are the methods I
In fact, this article should be called (1). After all, this article mainly focuses on theoretical knowledge and the previous article focuses on implementation formulas.
Map projection used by network maps such as Google Maps and Bing (it seems that Baidu map is also a mocato projection), which is often called Web Mercator, the main difference between it and conventional mocato
Because GIS describes the spatial information on the Earth's surface, it must be embedded in a spatial reference system, which is a coordinate frame, which is based on parameters such as ellipsoidal bodies. The three main coordinate systems currently used in China are: Beijing 1954, Xi ' an 1980 and WGS84.With the coordinate system, the ellipsoid, the data layer has geographic coordinates, which are the locations of the spherical surface with latitude and longitude. In order to be able to conver
Projection and reflection any part of the backlight of an object will produce a projection. if it is on a brighter surface, it will also reflect the reflection of the object, such as the water surface, glass desktop, marble floor, etc. So how to implement the projection effect? The following small series will introduce you to pss' realistic
Iphone/Ipad wireless projection to PC, Iphone Ipad projection pc
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Some projection technologies will inevitably be used for Demo presentation of applications. At this time, it seems a little bad to give a speech with a data line.
At this time, wireless
Confused for some time, today began to tidy up their own, but also to organize new knowledge.CSS3:Start from scratch: Now the most used in the page is the picture/container projection, text projection;Next, we summarize a projection problem:Box-shadow: Shadow type X-axis displacement y-axis displacement shadow size shadow extended shadow colorGenerally this write
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