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The link http://www.3dsoftware.com/Cartography/USGS/MapProjections/Azimuthal/Gnomonic does not exist. -- Jalanthomas 01:40, 5 March 2007 (UTC)
Geographical 'Gnomonic' projection refers to the use of the
gnomon or central, vertical (not axial) rod of a [
sun dial]. In a geographic Gnomonic projection, the central point (or gnomon) is chosen on the surface of the earth, to be convenient for the user, and all radii from that point represent '[
great circle] routes' thru the central point and its [
antipodal point] represented by the entire outer edge of a full earth projection.
In some forms, this can be
Azimuthal or a subset of special
Conic Projections, with a flat cone, or not, and the apex above or below the central point.
See also
Azmuthal Map generation.
The radii (or diameters) represent the Great Circle or shortest route between any two connected points. However the distances along these lines (sometimes represented by parallel circles) might or might not be
linear. Any non-radial measurements will vary from '1 times scale' at the central point (or contact circle), to 'infinity' at the antipode or perimeter, at which any land mass appears 'smeared out'. Often to minimize this disconcerting effect, the map is constrained to a small
portion of the earth and an altitude needed to connect the points of interest.
As a practical matter, the map is most useful to you only if centered on your own position, because it allows you to aim the trajectory of your airplane, cannon, or antenna more correctly toward any other point on the surface of the earth,without the distortion caused by more conventional mapping projections. Most obviously, east & west directions do not follow the parallels.
Weather,
Coriolis, and
geomagnetic effects, will all require trajectory compensation.
Wikidity (
talk) 20:19, 6 July 2010 (UTC)
If I understand rectilinear projection correctly (as exemplified by a pinhole camera), when some 'concentric rings' are equidistant on the spherical surface (globe) they cannot be equidistant on the plane surface (map) - and vice versa. Is this always true of gnomonic projection, or is rectilinear projection a special case of gnomonic projection ? -- Redbobblehat ( talk) 18:14, 14 February 2011 (UTC)
I will be replacing images on the various map projection pages. Presently many are on a satellite composite image from NASA that, while realistic, poorly demonstrates the projections because of dark color and low contrast. I have created a stylization of the same data with much brighter water areas and a light graticule to contrast. See the thumbnail of the example from another article. Some images on some pages are acceptable but differ stylistically from most articles; I will replace these also.
The images will be high resolution and antialiased, with 15° graticules for world projections, red, translucent equator, red tropics, and blue polar circles.
Please discuss agreement or objections over here (not this page). I intend to start these replacements on 13 August. Thank you. Strebe ( talk) 22:40, 6 August 2011 (UTC)
Note: Moved from my Talk page: Strebe, what is wrong with file I added?( Boss of 105 ( talk) 05:51, 3 April 2014 (UTC))
Hello! This is a note to let the editors of this article know that File:Gnomonic projection SW.jpg will be appearing as picture of the day on September 9, 2015. You can view and edit the POTD blurb at Template:POTD/2015-09-09. If this article needs any attention or maintenance, it would be preferable if that could be done before its appearance on the Main Page. Thanks! — Chris Woodrich ( talk) 00:21, 23 August 2015 (UTC)
Probably "any line segment on a gnomonic map" is geometrically correct, but it might be clarifying for a reader to add that this means a straight line. More so because the map (POTD today) shows circles. Even I, while familiar with this projection, had to check the definition of a line segment. (even worse: when I explain the great circle to people, I use the example of flying from the North pole over any meridian etc., which of course is a circle). - DePiep ( talk) 08:21, 9 September 2015 (UTC)
Hello fellow Wikipedians,
I have just modified one external link on Gnomonic projection. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
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First I saw this article years ago. It had formulas and links, and there were no interactive map that user could scroll or zoom. In later years, I checked this more times and there were no interactive map still. Now, I insert a link for it and it gets retracted like it was spam. So I guess I have to spent 30 minutes of my life to provide justification for a person who reverted it in 5 seconds (like it was spam).
https://www.humus.name/index.php?page=Cubemap&item=Earth
Just because it was on someone's personal site? Well this page is more relevant to article than any other links, which tell same information already existing in the article. Meanwhile the article has Sphaerica link is useless for majority of wikipedia users -- virtually nobody going to install it. I did, and was puzzled - WTF- how is it even relevant to the article?
Do you suggest anyone wishing to take a look at gnomonic Earth map install some proprietary software, or write their own implementation? Don't like the link? Find a better one, then delete it. Google maps isn't going to add option to use gnomonic projection anytime soon. Alliumnsk ( talk)
The article notes that a gnomonic projection is centered on a point on the surface of the Earth. So far, so good. However, some of the illustrations are described as being "centered on" a line, such as the Equator or the 40th parallel. These are not points, and it's been bothering me that the captions are leaving it at that. Ideally, these captions should identify the point at which the projection is tangent to the Earth's surface (e.g., the North Pole). If that level of precision is not possible, the caption should say something like "a point on the Equator" or "a point near 40°N 75°W" to be completely accurate. Piledhigheranddeeper ( talk) 16:26, 30 October 2023 (UTC)
This article is rated Start-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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The link http://www.3dsoftware.com/Cartography/USGS/MapProjections/Azimuthal/Gnomonic does not exist. -- Jalanthomas 01:40, 5 March 2007 (UTC)
Geographical 'Gnomonic' projection refers to the use of the
gnomon or central, vertical (not axial) rod of a [
sun dial]. In a geographic Gnomonic projection, the central point (or gnomon) is chosen on the surface of the earth, to be convenient for the user, and all radii from that point represent '[
great circle] routes' thru the central point and its [
antipodal point] represented by the entire outer edge of a full earth projection.
In some forms, this can be
Azimuthal or a subset of special
Conic Projections, with a flat cone, or not, and the apex above or below the central point.
See also
Azmuthal Map generation.
The radii (or diameters) represent the Great Circle or shortest route between any two connected points. However the distances along these lines (sometimes represented by parallel circles) might or might not be
linear. Any non-radial measurements will vary from '1 times scale' at the central point (or contact circle), to 'infinity' at the antipode or perimeter, at which any land mass appears 'smeared out'. Often to minimize this disconcerting effect, the map is constrained to a small
portion of the earth and an altitude needed to connect the points of interest.
As a practical matter, the map is most useful to you only if centered on your own position, because it allows you to aim the trajectory of your airplane, cannon, or antenna more correctly toward any other point on the surface of the earth,without the distortion caused by more conventional mapping projections. Most obviously, east & west directions do not follow the parallels.
Weather,
Coriolis, and
geomagnetic effects, will all require trajectory compensation.
Wikidity (
talk) 20:19, 6 July 2010 (UTC)
If I understand rectilinear projection correctly (as exemplified by a pinhole camera), when some 'concentric rings' are equidistant on the spherical surface (globe) they cannot be equidistant on the plane surface (map) - and vice versa. Is this always true of gnomonic projection, or is rectilinear projection a special case of gnomonic projection ? -- Redbobblehat ( talk) 18:14, 14 February 2011 (UTC)
I will be replacing images on the various map projection pages. Presently many are on a satellite composite image from NASA that, while realistic, poorly demonstrates the projections because of dark color and low contrast. I have created a stylization of the same data with much brighter water areas and a light graticule to contrast. See the thumbnail of the example from another article. Some images on some pages are acceptable but differ stylistically from most articles; I will replace these also.
The images will be high resolution and antialiased, with 15° graticules for world projections, red, translucent equator, red tropics, and blue polar circles.
Please discuss agreement or objections over here (not this page). I intend to start these replacements on 13 August. Thank you. Strebe ( talk) 22:40, 6 August 2011 (UTC)
Note: Moved from my Talk page: Strebe, what is wrong with file I added?( Boss of 105 ( talk) 05:51, 3 April 2014 (UTC))
Hello! This is a note to let the editors of this article know that File:Gnomonic projection SW.jpg will be appearing as picture of the day on September 9, 2015. You can view and edit the POTD blurb at Template:POTD/2015-09-09. If this article needs any attention or maintenance, it would be preferable if that could be done before its appearance on the Main Page. Thanks! — Chris Woodrich ( talk) 00:21, 23 August 2015 (UTC)
Probably "any line segment on a gnomonic map" is geometrically correct, but it might be clarifying for a reader to add that this means a straight line. More so because the map (POTD today) shows circles. Even I, while familiar with this projection, had to check the definition of a line segment. (even worse: when I explain the great circle to people, I use the example of flying from the North pole over any meridian etc., which of course is a circle). - DePiep ( talk) 08:21, 9 September 2015 (UTC)
Hello fellow Wikipedians,
I have just modified one external link on Gnomonic projection. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.
An editor has reviewed this edit and fixed any errors that were found.
Cheers.— InternetArchiveBot ( Report bug) 07:04, 20 October 2017 (UTC)
First I saw this article years ago. It had formulas and links, and there were no interactive map that user could scroll or zoom. In later years, I checked this more times and there were no interactive map still. Now, I insert a link for it and it gets retracted like it was spam. So I guess I have to spent 30 minutes of my life to provide justification for a person who reverted it in 5 seconds (like it was spam).
https://www.humus.name/index.php?page=Cubemap&item=Earth
Just because it was on someone's personal site? Well this page is more relevant to article than any other links, which tell same information already existing in the article. Meanwhile the article has Sphaerica link is useless for majority of wikipedia users -- virtually nobody going to install it. I did, and was puzzled - WTF- how is it even relevant to the article?
Do you suggest anyone wishing to take a look at gnomonic Earth map install some proprietary software, or write their own implementation? Don't like the link? Find a better one, then delete it. Google maps isn't going to add option to use gnomonic projection anytime soon. Alliumnsk ( talk)
The article notes that a gnomonic projection is centered on a point on the surface of the Earth. So far, so good. However, some of the illustrations are described as being "centered on" a line, such as the Equator or the 40th parallel. These are not points, and it's been bothering me that the captions are leaving it at that. Ideally, these captions should identify the point at which the projection is tangent to the Earth's surface (e.g., the North Pole). If that level of precision is not possible, the caption should say something like "a point on the Equator" or "a point near 40°N 75°W" to be completely accurate. Piledhigheranddeeper ( talk) 16:26, 30 October 2023 (UTC)