projection

问题 I want to create a oblique (cavalier) projection in OpenGL. I know this operation is not default supported and instead I need a Shear Matrix and then make an Orthogonal Projection. Can you tell me what are the OpenGl steps / functions that I have to make? 回答1: I've not used a oblique/cavalier projection before, but the following should give you an idea of how to proceed: Create a 4x4 shear matrix, H(θ, Φ) = | 1, 0, -cot(θ), 0 | | 0, 1, -cot(Φ), 0 | | 0, 0, 1, 0 | | 0, 0, 0, 1 | θ being the

问题 I want to create a oblique (cavalier) projection in OpenGL. I know this operation is not default supported and instead I need a Shear Matrix and then make an Orthogonal Projection. Can you tell me what are the OpenGl steps / functions that I have to make? 回答1: I've not used a oblique/cavalier projection before, but the following should give you an idea of how to proceed: Create a 4x4 shear matrix, H(θ, Φ) = | 1, 0, -cot(θ), 0 | | 0, 1, -cot(Φ), 0 | | 0, 0, 1, 0 | | 0, 0, 0, 1 | θ being the

问题 I am confused about perspective projection. Here is the scenario that is confusing me. My frustrum's front plane is basically positioned at at positive z-axis and the back plane at a negative axis and rotated about some deg along the posive z-axis. Now, whenever I go through examples I see that the near and the far plane are all present in the negative z axis. My approach in this case was basically something like: glMatrixMode(GL_PROJECTION); glLoadIdentity(); glFrustrum(-xval,+xval,-yval,

问题 I am confused about perspective projection. Here is the scenario that is confusing me. My frustrum's front plane is basically positioned at at positive z-axis and the back plane at a negative axis and rotated about some deg along the posive z-axis. Now, whenever I go through examples I see that the near and the far plane are all present in the negative z axis. My approach in this case was basically something like: glMatrixMode(GL_PROJECTION); glLoadIdentity(); glFrustrum(-xval,+xval,-yval,

问题 How can I filter fields with the mongo-go-driver. Tried it with findopt.Projection but no success. type fields struct { _id int16 } s := bson.NewDocument() filter := bson.NewDocument(bson.EC.ObjectID("_id", starterId)) var opts []findopt.One opts = append(opts, findopt.Projection(fields{ _id: 0, })) staCon.collection.FindOne(nil, filter, opts...).Decode(s) In the end, I want to suppress the field "_id". But the documents didn't change. 回答1: The reason why it doesn't work for you is because

问题 I'd like to get homography matrix to Bird's eye view and I know the projection Matrix of the camera. Is there any relation between them? Thanks. 回答1: A projection matrix is defined as a product of camera's intrinsic (e.g. focal length, principal points, etc.) and extrinsic (rotation and translation) matrices. The question is w.r.t what your rotation and translation are? For example, I can imagine another camera or an object in 3D with respect to which you have these rotations and translations

问题 I'd like to get homography matrix to Bird's eye view and I know the projection Matrix of the camera. Is there any relation between them? Thanks. 回答1: A projection matrix is defined as a product of camera's intrinsic (e.g. focal length, principal points, etc.) and extrinsic (rotation and translation) matrices. The question is w.r.t what your rotation and translation are? For example, I can imagine another camera or an object in 3D with respect to which you have these rotations and translations

问题 Is it possible to return an entity using a projection query? I've successfully done it with a SQL query (see below), but can't find how to do it with a projection query. Dim sql As String = "SELECT {a.*}, {b.*} FROM a LEFT OUTER JOIN b ON a.pk = b.fk") ' Convert SQL results into entities {a} and {b} Dim query As IQuery = session.CreateSQLQuery(sql) _ .AddEntity("a", GetType(a)) _ .AddEntity("b", GetType(b)) Return query.List() 回答1: Yes, you can return entities from projection queries. If you

问题 I'm trying to project a set of points ([long, lat] tuples) on top of an SVG map of my home country Austria: https://commons.wikimedia.org/wiki/File:Austria-geographic_map-blank.svg The description of the SVG file on Wikimedia gives a projection name and the bounds of the map: Lambert Conformal Conic, WGS84 datum Geographic limits of the map: West: 17.2° W East: 9.3° W North: 49.2° N South: 46.0° N Naive as I am, I thought this information would be enough to create the right kind of projection

问题 Reading the documentation on Cloud Datastore, it's pretty clear that a Get retrieves the entire entity, and that a query is always done against the index. Here's where it gets confusing, because according to the documentation: Projection queries allow you to query Cloud Datastore for just those specific properties of an entity that you actually need, at lower latency and cost than retrieving the entire entity But if all queries are done against an index, a query would never retrieve the