Talk:Parallel projection

On the cancelation of my new version
User: SharkD removed my new version. The current (old) version has essential drawbacks:

(1) Parallel projection is nowhere defined.

(2) Essential properties for the descriptive geometry are not mentioned.

(3) The article is on parallel projection and not on pictorials, which take a lot of space !

I concede, my English is not the best and would appreciate a slightly more support than just to remove my edits.--Ag2gaeh (talk) 14:58, 20 April 2017 (UTC)
 * The old (current) version of this page has serious problems as outlined above. 's work should not have been dismissed in the way it was. However, the page is of interest to both mathematicians and computer graphics people and these audiences have different expectations for what should be in this page. I suspect that neither version would be seen as satisfactory by both of these groups, so I would suggest a melding of these versions. --Bill Cherowitzo (talk) 16:58, 20 April 2017 (UTC)
 * He replaced the entire text in one single edit with no prior discussion. How is that any more warranted? He was bold, I reverted. WP:BRD SharkD   Talk  17:53, 21 April 2017 (UTC)
 * I agree that the lead of the previous version was very poor. However with this new version, you have unduly removed relevant material. In fact the article must have two parts: a mathematical part, for which your version is a good starting point, although it needs some improvement to satisfy the standard of MOS:MATH, and a part devoted to applications in drawing, for which the body of the old version is a useful basis. Thus the two versions have to be merged. For this merge, the challenge is to make reading possible for people that are interested in drawing, and do not know anything in mathematics. D.Lazard (talk) 17:04, 20 April 2017 (UTC)
 * , If one or both of you could please translate Ag2gaeh's version into proper English in user space before adding it to article space, it would be very helpful. I found it to be unintelligible. This is English Wikipedia and its content needs to be understandable.  SharkD   Talk  09:01, 21 April 2017 (UTC)
 * @User:SharkD: Please could You give some examples of my "not understandable" English. Meanwhile, I give an example from the present version, which is not understandable (only for me?):  Parallel projections have lines of projection that are parallel both in reality and in the projection plane. (The first sentence of Your favorite version.) What do You mean by "reality", "projection lines in the projection plane" (??). Are our problems perhaps math and not English ?--Ag2gaeh (talk) 10:29, 21 April 2017 (UTC)
 * It means that lines that are parallel in reality remain parallel in the projected image. SharkD   Talk  14:15, 21 April 2017 (UTC)
 * Additional remarks: I am editing here (English Wiki) since 2013. You are the first, who removed an edit because of my "poor" English. You should not treat me like an incapable pupil, who needs some watchdogs. If there are some problems, we should discuss and solve them, together. --Ag2gaeh (talk) 12:09, 21 April 2017 (UTC)
 * Your writing is full of grammar mistakes, and the fact that this is a very technical subject exacerbates the issue. I don't see why you don't understand this and think *I am* the one who is being unreasonable. We have a duty to our readers to be clear and use correct English. Frankly, I find your attitude insulting to people who visit Wikipedia.
 * And, the problem is not just limited to this article, but exists in Axonometric projection as well. (See our previous discussion for reference.) If *I* can't understand what you write, I'm sure our readers won't either. SharkD   Talk  13:51, 21 April 2017 (UTC)
 * Axonometry is another article Ag2gaeh just created that is full of grammatical errors. Is there a MOS policy on proper use of English grammar? SharkD   Talk  14:30, 21 April 2017 (UTC)

Please read WP:NNS, and particularly the sentence Don't criticise poor English. That's about as helpful and gracious as criticising a pregnant woman for getting in your way when she's slower than you are climbing onto a bus. Instead fix it. If you see a grammar error, fix it. If, because of the error, you cannot understand the sentence, ask in the talk page or use the clarify template. Please stop criticising in such a vague way. Personally I do not see, in 's edits, any grammar error that makes a sentence not understandable or confusing. On the other hand, in the lead that you have restored, there many grammatical errors that are highly confusing. For example: "within parallel projection" (lacking article + what is the interior of a projection?). "Because pictorial projections innately contain" (how a projection can contain something?); "this distorsion" (to what refers "this"); "in the rote, drawing instrument for pictorials" (where is the verb of the part of the sentence?) ... D.Lazard (talk) 15:41, 21 April 2017 (UTC)
 * Parallel projection is a class, category or collection of projection types. Within that class, are sub-types. There's nothing wrong with using the word "within" in this context. Something can be "within" a category (examples). The noun form of projection is synonymous with "image", and an image can contain lots of things (examples). The "distortion" is a leftover from a very old version of the text that I haven't been able to decipher yet.
 * On the other hand, I can't get through the first sentence of Ag2gaeh's version: "A parallel projection is a mapping of the points of the Euclidean space onto a prescribed plane, the projection plane or image plane, using parallel rays (lines)." Why "the" points and "the" Euclidean space? Are the prescribed plane, the projection plane, and the image plane three different things? What is a "prescribed plane"? Since when are rays and lines the same things? THE WHOLE ARTICLE IS JUST LIKE THIS!!
 * And NOBODY is going to come help me clear up all this confusion. And don't suggest I can go to Village Pump and ask for help. NOBODY IS GOING TO RESPOND. Just like last time this happened with Ag2gaeh's garbled writing. Whereas the article as it is currently is, except for the lead maybe, well-written in PLAIN ENGLISH. SharkD   Talk  16:10, 21 April 2017 (UTC)
 * That's an awful lot of shouting considering that this is the first concrete example that you've raised! You have several people engaging with you here, now -- instead of complaining about the difficulty of getting engagement, you should take advantage of the opportunity.  As for the issues that you've raised: "the Euclidean space" is a common awkward use of articles by a non-native English speaker and is easy to fix.  "Prescribed" is a standard English word, used correctly, albeit in a somewhat jargon-y way.  Saying that this is a "grammar problem" is both wrong and unhelpful.  The phrase "verbed onto X, the Y or Z, using ..." is a grammatically correct English construction: it means that X is one of the things called Y or Z.  This long sentence might be hard to understand because it contains a lot of information, and maybe would be clearer if it were broken up, but this has nothing to do with English grammar, it has to do with writing style.  Ag2gaeh's version is mathematician-y, and there is some value in having this article written in an accessible way, but many of his edits are clear improvements (e.g., the first sentence of the previous version is totally mystifying).  If you would stop shouting and instead work collaboratively with Ag2gaeh, I think much good could come of this.  --JBL (talk) 17:28, 21 April 2017 (UTC)
 * "verbed onto X, the Y or Z, using ..." should be "verbed onto X&mdash;the Y or Z&mdash;using ..." no? Also, what is "prescribed" supposed to mean in this case? As for the shouting, this not is first time I've tried to work with Ag2gaeh. The last time I sought assistance in puzzling out what he was trying to say I attracted a drive-by post, too, but nothing lasting. Would you have posted here unprovoked?  SharkD   Talk  17:38, 21 April 2017 (UTC)


 * The lead, although improved, is still far from adequate. I have revised 's edit a bit, making it a bit less edgy. Perhaps this can be used as a starting point of a full merger.--Bill Cherowitzo (talk) 18:52, 21 April 2017 (UTC)
 * A parallel projection of an object in three-dimensional space onto a fixed plane, known as the projection plane or image plane, uses rays (lines of sight or projection lines) that are parallel to each other. It is a basic tool in descriptive geometry. The projection is called orthographic, if the rays are perpendicular (orthogonal) to the image plane, otherwise the projection is called oblique or skew (see axonometric projection). A parallel projection can be seen, technically, as the limit of a central projection (where the rays pass through a fixed point, called the center), as the center is moved towards infinity. Although a central projection of an object may be seen as more realistic compared with a parallel projection, a parallel projection is often a more popular representation, because the parallelism of lines in the object is preserved in the image. Amongst the parallel projections, the orthographic projections are the most realistic ones and they are commonly used by engineers. Certain types of oblique projections (cavalier projection, military projection, isometric projections) are rather simple to implement and are used for quick pictorials of objects.
 * In order to prevent any confusion, one should be aware that the expression parallel projection is used in the literature for both the procedure (a mathematical mapping function) as well as for the resulting image produced by the procedure.
 * I have tweaked it as well, and am pretty happy with it. SharkD   Talk  16:54, 24 April 2017 (UTC)

Part one
I will post several items here from several articles, since they are all related. SharkD  Talk  18:18, 21 April 2017 (UTC)
 * Firstly, in Axonometric projection, what do you mean by "general defined"? Is "general" a noun, adjective or adverb? SharkD   Talk  18:18, 21 April 2017 (UTC)
 * fixed --Ag2gaeh (talk) 08:22, 22 April 2017 (UTC)
 * Thanks. SharkD   Talk  21:28, 29 April 2017 (UTC)


 * In Axonometry, what does "Only for special parameters (images of the axes, forshortenings)" mean? Are the forshortenings parameters or images? SharkD   Talk  18:18, 21 April 2017 (UTC)
 * In Parallel projection, why are "isometric projections" listed among types of "oblique projections"? The image plane is orthogonal to the viewing axis in isometric projection. SharkD   Talk  18:18, 21 April 2017 (UTC)
 * In axonometry isometric axonometry means only that all forshortenings are equal (see lit.). Computergraphics uses exclusively the standard isometry (see axonometry)--Ag2gaeh (talk) 08:22, 22 April 2017 (UTC)
 * I am talking about "isometric projection" not "isometric axonometry". The reader expects something different than what you have described. SharkD   Talk  00:00, 23 April 2017 (UTC)


 * In Parallel projection I don't think either image is very good without a more explanatory caption. SharkD   Talk  18:18, 21 April 2017 (UTC)
 * in Axonometry, what are "nice" pictures, "suitable" choices and "good" images? This needs to be explained. SharkD   Talk  18:18, 21 April 2017 (UTC)
 * fixed --Ag2gaeh (talk) 08:22, 22 April 2017 (UTC)
 * You still have not explained what is "suitable" and what is not "suitable". It is not fixed. SharkD   Talk  00:08, 23 April 2017 (UTC)


 * In File:Axonometry-var14.svg, what do "distorted" and "convenient" mean? These need to be explained as well. SharkD   Talk  18:18, 21 April 2017 (UTC)
 * fixed --Ag2gaeh (talk) 08:22, 22 April 2017 (UTC)


 * In Axonometry I have no idea what is going on in File:Axonom-def0.svg. The caption does not explain anything. SharkD   Talk  18:18, 21 April 2017 (UTC)
 * The picture is an optical support for the text nearby.--Ag2gaeh (talk) 08:22, 22 April 2017 (UTC)


 * In File:Axo-parameter-spec.svg, in the first image, why does v_x equal 0.5, but the axis is not drawn half as long?  SharkD   Talk  18:18, 21 April 2017 (UTC)
 * It is just a sketch.--Ag2gaeh (talk) 08:22, 22 April 2017 (UTC)
 * Could you recreate the image such that v_x, v_y and v_z are drawn to the dimensions stated in the text? SharkD   Talk  02:18, 23 April 2017 (UTC)


 * In File:Axo-parameter-spec.svg, since this is English Wikipedia, the symbol for a right angle should be a square not an arc. SharkD   Talk  18:18, 21 April 2017 (UTC)
 * Is this a problem ?--Ag2gaeh (talk) 08:22, 22 April 2017 (UTC)
 * I would not have mentioned it if it wasn't a problem. SharkD   Talk  00:33, 23 April 2017 (UTC)


 * In File:Axo-parameter-spec.svg, in the fourth image, how can v_x, v_y, v_z, and v all be equal? v_x, v_y, v_z are numbers, v is a vector. They can't be equal. SharkD   Talk  18:18, 21 April 2017 (UTC)
 * By its definition v is the common value of the forshortenings, hence a number.--Ag2gaeh (talk) 08:22, 22 April 2017 (UTC)
 * Since v does not appear anywhere else in the article and serves no real purpose, could you remove it? SharkD   Talk  02:18, 23 April 2017 (UTC)


 * In File:Axo-parameter-spec.svg, in the second image, how can alpha be free? I've never seen the vertical axis anything other than vertical in military perspective. Where did you get this idea from? SharkD   Talk  18:18, 21 April 2017 (UTC)
 * fixed in def. of the prcedure.--Ag2gaeh (talk) 08:22, 22 April 2017 (UTC)


 * In File:Axo-parameter-spec.svg, in the fourth image, I have never seen isometric perspective with anything other than 120 degree angles. Why did you mark them as "free"? SharkD   Talk  18:18, 21 April 2017 (UTC)
 * In axonometry isometric axonometry means only that all forshortenings are equal (see lit.). Computergraphics uses exclusively the standard isometry (see axonometry) and calls it isometry.--Ag2gaeh (talk) 08:22, 22 April 2017 (UTC)


 * In File:Cube-parallel-proj-s.svg, I think the image plane in both of the top images should be horizontal. Placing one of them at an angle is going to confuse readers. (It confused me.) SharkD   Talk  18:18, 21 April 2017 (UTC)
 * The image plane can be any plane. If You like horizontal planes more, You may restrict Yourself to such planes.--Ag2gaeh (talk) 08:22, 22 April 2017 (UTC)
 * By changing the angle of the plane in the image, you are introducing an additional variable that is not explained to the reader. You should limit the number of variables as much as possible in order to avoid confusing him or her. Please give both planes the same orientation. SharkD   Talk  00:53, 23 April 2017 (UTC)


 * In Parallel projection, by "central projection" do you mean "perspective projection"? What do you mean by "pass a fixed point"? Do they pass next to, around, or through the point? SharkD   Talk  18:18, 21 April 2017 (UTC)
 * In geometry central projection is more common.--Ag2gaeh (talk) 08:22, 22 April 2017 (UTC)
 * This article is not just for geometers, however. You need to make the article clear for everyone who uses this article. I think people are more familiar with "perspective projection" than "central projection". SharkD   Talk  00:31, 23 April 2017 (UTC)

I'll try and come up with some more soon. SharkD  Talk  18:18, 21 April 2017 (UTC)


 * Thanks for Your remarks. See my comments above.--Ag2gaeh (talk) 08:22, 22 April 2017 (UTC)

Part two

 * In File:Axo-parameter-gen.svg you are missing gamma. SharkD   Talk  00:10, 23 April 2017 (UTC)
 * gamma is determined by alpha and beta, which are freely selected. Perhaps I should add it.--Ag2gaeh (talk) 09:05, 23 April 2017 (UTC)
 * Considering that you describe the parameter in the text next to the image, yes you should. SharkD   Talk  09:18, 24 April 2017 (UTC)


 * In Axonometry it says, "Choose suitable images of the coordinate axes, not contained in a line." What is "suitable" and how can an image be contained in a line? SharkD   Talk  00:14, 23 April 2017 (UTC)
 * In order to get images, which look "spatial", two images of coordinate axes should not be incident. If the three images of the coordinate axes would be contained in a line, the procedure whould not work. The best thing is: make your own experiments.--Ag2gaeh (talk) 09:05, 23 April 2017 (UTC)
 * The first problem is that "image" is the wrong word to use. You should use a different word, such as "projection". You should also explain why the procedure will not work instead of relying on the reader to "make his own experiments". If the reader is supposed to make his own experiments, then we don't need an article at all. SharkD   Talk  09:14, 24 April 2017 (UTC)


 * In Axonometry, you link to de:orthogonale Axonometrie in the article text. I don't think this is appropriate. Please explain what you're trying to say in English instead. SharkD   Talk  00:22, 23 April 2017 (UTC)
 * I added a ref. Only in German. Perhaps you find an English ref. Perhaps I translate the German article, sometimes.--Ag2gaeh (talk) 09:05, 23 April 2017 (UTC)


 * In Axonometry, it says "The parameters of the first diagram (on graph paper)..." Which diagram? It is not clear. Is "graph paper" important? Otherwise I would remove it. SharkD   Talk  00:25, 23 April 2017 (UTC)
 * The first diagram of the article. Yes "graph paper" is important, because most people   get in contact (at school) with axonometry using graph paper. Is "graph paper" the right translation of the German "Karopapier" ?--Ag2gaeh (talk) 09:05, 23 April 2017 (UTC)
 * I didn't understand which image you were referring to. "First" could mean first in the chapter, or first somewhere else. You can't rely on an image always remaining located in the same place in the article over time. Things change. So you should avoid such descriptions. SharkD   Talk  09:18, 24 April 2017 (UTC)


 * In File:Axonom-def0.svg could you mark v_x, v_y and v_z as well? SharkD   Talk  02:38, 23 April 2017 (UTC)
 * The forshortenings are represented by the images of the three edges of the unitcube, which contain the origin.--Ag2gaeh (talk) 09:05, 23 April 2017 (UTC)
 * I don't see any cube in that image, or an explanation in the text. Neither will our readers. SharkD   Talk  09:19, 24 April 2017 (UTC)
 * I inserted my replies above.--Ag2gaeh (talk) 09:05, 23 April 2017 (UTC)

Part three

 * Note that I still have unanswered questions in Parts one and two. SharkD   Talk  10:12, 24 April 2017 (UTC)
 * You need to capitalize the words in your images. For instance, "general axonometry" in File:Axo-parameter-gen.svg needs to be capitalized. Is this not also true in the German language? SharkD   Talk  09:52, 24 April 2017 (UTC)
 * In Axonometry, it says, "the image is a scaled orthographic projection with scale factor {\displaystyle {\sqrt {1.5}}=1.225} {\displaystyle {\sqrt {1.5}}=1.225}. Hence the image has a good impression and the contour of a sphere is a circle." What effect does the scaling have on whether the contour of a sphere is a circle? To me it seems the scaling has zero effect as long as it is uniform. SharkD   Talk  10:11, 24 April 2017 (UTC)
 * In Axonometry, it says, "Axonometry is a graphical procedure of descriptive geometry that generates a planar image of a 3-dimensional object. Its name indicates that coordinate axes and the coordinates of essential points play a crucial role." This is rather awkward and needs to be rephrased. I'm sure that coordinate axes and essential points play a crucial role in just about every plot or graph. I'm not sure what you're trying to say. SharkD   Talk  17:19, 24 April 2017 (UTC)

,,, Would any of you care to participate in this discussion? SharkD  Talk  04:45, 26 April 2017 (UTC)


 * I am confused, the comments in this section are about a different article, right? Why are they on this talk-page?
 * Separately, I have just done a bunch of polishing on this article. I like it, although I think that it doesn't navigate entirely smoothly the issue of speaking to two different audiences (draftspeople and mathematicians).  The previous sections, with multiple in-line threads intertwined, are difficult to parse; if there are things you are still unhappy about in the present form of the article, perhaps you could re-collect them in a new section on this talk page?  --JBL (talk) 17:29, 29 April 2017 (UTC)
 * The above questions are about a series of closely related articles and images recently created by Ag2gaeh, who seems to have abandoned us. I have no more questions about Parallel projection however. SharkD   Talk  20:53, 29 April 2017 (UTC)
 * I take that back. I do have another question about this article, which I have placed in "Part four". SharkD   Talk  21:27, 29 April 2017 (UTC)

Part four

 * In Parallel projection I am not sure I understand this statement: "The length of a line segment parallel to the projection plane remains unchanged. The length of any line segment is shortened if the projection is an orthographic one." I think the second sentence only applies if the line segment is *not* parallel to the projection plane. Not 100% sure. SharkD   Talk  21:24, 29 April 2017 (UTC)

Axonometric projection
I recommend to reduce the section on axonometric projection and insert a link via mainarticle to axonometric projection.--Ag2gaeh (talk) 14:10, 22 April 2017 (UTC)
 * I have been looking over the articles again, and have come to a reconsideration. Having two definitions for axonometry/axonometric projection may be too confusing for readers. Currently, according to your research, there is no practical difference between parallel projection and axonometric projection as far as I can tell. They seem to be the same thing. Maybe we should just keep axonometry and redirect axonometric projection to it instead of having both? SharkD   Talk  02:11, 23 April 2017 (UTC)
 * Of course, then we should move the "History" and "Limitations" sections to here. SharkD   Talk  02:43, 23 April 2017 (UTC)
 * Parallel projection is not the same thing as axonometric projection ! Parallel projection includes oblique projections and has at first nothing to do with any axonometry ! The result of our discussion on this subject was: English literature considers axonometric projection as an orthogonal axonometry and is not the same as axonometry (which includes oblique axonometry). A redirect from axonometric projection to axonometry would not be appropiate, because orthogonal axonometry needs an extra article and is not discussed in detail in the article  axonometry (see the German article on orthogonale Axonometrie).
 * There should be the articles parallel projection (includes oblique projection), axonometry (includes oblique axonometry) and orthogonal axonometry = axonometric projection (an important special axonometry).--Ag2gaeh (talk) 08:41, 23 April 2017 (UTC)
 * I think the actual result of our last discussion was that the (English) sources are totally inconsistent. See Survey of sources. Axonometric projection could mean orthogonal axonometry, or it could mean something else. Maybe since the sources are so inconsistent, we should go with the idea that axonometric projection is synonymous with axonometry, instead of the current definitions? SharkD   Talk  09:08, 24 April 2017 (UTC)
 * I examined the same sources again in more detail, and withdraw my proposal. SharkD   Talk  23:11, 25 April 2017 (UTC)
 * I moved some of the content around, and think it would be okay to now remove the "Pictorials" section. SharkD   Talk  23:28, 25 April 2017 (UTC)

Merger proposal
I propose to merge Axonometric projection into this article. As explained in a lengthy discussion on that article's Talk page, in German literature "axonometric projection" is synonymous with "parallel projection", and in English literature the terms are used wildly inconsistently. I suggest we go by the German usage, and explain any differences where necessary. Thanks. By the way, I was formerly known as SharkD, and participated in the discussions with Ag2gaeh. &#x27A7; datumizer   &#9742;  00:09, 10 May 2021 (UTC)
 * I kind of already went ahead with a lot of this without considering it. The original confusion about this article was totally my fault. Ag2gaeh was right. Sorry. &#x27A7; datumizer   &#9742;  00:53, 10 May 2021 (UTC)
 * I do not want to enter a new discussion. In German literature: a) A parallel projection is a special kind of mapping. b) Axonometry is a special techniques to perform a parallel projection (orthographic and oblique). It uses axes and coordinates. Both terms are not equivalent.
 * What "axonometric projection" in English literature means should be described by persons, who are familiar with it.--Ag2gaeh (talk) 07:18, 10 May 2021 (UTC)
 * Yes! If you could summon them to this discussion, it would be ideal. &#x27A7; datumizer   &#9742;  01:06, 12 May 2021 (UTC)
 * Again, a past survey of sources I did can be found here. &#x27A7; datumizer   &#9742;  01:02, 12 May 2021 (UTC)
 * &#x27A7; datumizer   &#9742;  01:06, 12 May 2021 (UTC)
 * Thanks for the ping, but I do not understand the broader context here well enough to have an opinion. --JBL (talk) 14:41, 23 May 2021 (UTC)
 * Closing, given that the discussion is stale for more than a year, and without consensus. Klbrain (talk) 09:53, 5 September 2022 (UTC)