Needs Pictures Needs Pictures:  0
Picture(s) thanks Picture(s) thanks:  0
Page 1 of 3 123 LastLast
Results 1 to 15 of 31
  1. #1
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    422

    Default Converting Photo to Orthographic Drawing

    I have searched the web for a simple description of the Descriptive Geometry projections to convert a perspective photograph into an engineering drawing (3rd angle orthographic).

    There are lots of discussions on the relationships between views, how to draw in perspective with arbitrary assumptions, deep technical texts on multilayered projections and lots of software matrix conversion theory - but no simple procedure that I could find.

    I think I have developed the simple drawing projections to convert an orthographic drawing into a perspective sketch, and I intend to try and work those projections backwards.

    I do not need any references to software routines or fancy photo manipulation programs, just the projections that one could utilize with pencil and ruler on a drawing board.

    Can anyone point me to a suitable source ?
    Is anyone interested in discussing the problem ?

    The particular immediate application for me is a photo of a very old electric narrow-gauge locomotive that I will like to model in 5 inch gauge.

    John.

  2. # ADS
    Google Adsense Advertisement
    Join Date
    Always
    Location
    Advertising world
    Posts
    Many





     
  3. #2
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    422

    Default

    Well, I thought that this was not a trivial question, and after 128 views without any comments, it may be harder than I thought.

    It seems to me that the solution must involve an iterative approach with rough approximations, a trial development, and then to modify the approximations towards, hopefully, the correct solution.

    I have some ideas that I will report on once I have proved them.
    John

  4. #3
    Mobyturns's Avatar
    Mobyturns is offline In An Instant Your Life Can Change Forever
    Join Date
    Jul 2012
    Location
    "Brownsville" Nth QLD
    Age
    66
    Posts
    4,411

    Default

    Some of your answers will lie in researching aerial photogrammetry. However terrestrial photogrammetry will have more application to your task as it is widely used in applications such as building conservation these days. The solution is much simpler with flat building facades which at least have parallel & orthogonal planes over the types of surfaces found on machinery.

    Photos are a central point perspective where scale varies continuously proportional to "depth" (distance from lens) in the photograph and point of interests offset from the "axis" of the photograph. Those relationships are well understood with aerial & terrestrial mapping and photogrammetry. Originally analytical (mechanical) stereo plotters were used with stereo pairs of image, usually with an offset or overlap of 60% forward & 25% side, to take measurements in the "stereo model." The stereo model is formed by rectifying the photo pairs first, a process of manipulating the plane of the photograph then bring them into orientation to form a stereo model.

    Unfortunately it is not a trivial exercise but it can be done with well taken images and a simple stereo-scope, or a stereo-comparator if you just happen to have one lying about.

    Back to your problem - a simple solution - Scale errors can be controlled in a simple image if the image coverage (area) is limited and the depth of field is not to great, so lots of small area images of components if you have access to the subject.

    http://petriefied.info/Petrie_Britis...n_fulltext.pdf

    As an aside, If you are doing this for historical machinery conservation purposes there are very modern surveying instruments that can easily scan an object producing 3D point clouds that are then modeled into 3D surfaces etc. Accuracy of a few mm or better is achievable. These instruments are used routinely in modern surveying practices but producing working drawings will not be a cheap exercise.
    Mobyturns

    In An Instant Your Life CanChange Forever

  5. #4
    Join Date
    Dec 2010
    Location
    Oberon NSW
    Age
    40
    Posts
    117

    Default

    Couple quick questions about the photos and camera.

    Do you know how far the photographer was standing from the object?
    Have you had the distortions on the camera lens mapped?
    How accurate do the measurements need to be?

    I ask because camera lenses have flaws. There will be minute variations in thickness and density in the lens that will distort how the object is recorded in the image and thereby affect your measurements. How close the person is to the object will cause parallax and you'll have to know the distance between the object and the photographer to compensate for distortion from nadir.

    But if your measurements don't need to be very accurate, than the issues may be glossed over.

  6. #5
    Join Date
    May 2011
    Location
    Murray Bridge SA
    Posts
    3,339

    Default

    I see the question as a bit vague, but that could be me . From memory of art at school, everything meets at a point in the distance, if 2 lines appear parallel, they will meet eventually. The way I do scaling, is to enlarge the photo up to a size that is workable to get the fine details required. As the width or length is known or can be found, scaling can be worked out, ie. if it's 8' wide and you want to go to 5", I divide 96" (8'X12" = 96) X 5 =19.2. I scale the enlargement to correct full size then divide it by 19.2, which then gives me my scaled size.
    Kryn

  7. #6
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    422

    Default

    Thanks for all the comments.

    The photo of the prime subject was taken in the 60's from an unknown height, distance and oblique view.
    These are the factors that determine the projections to get the orthogonal drawing.

    The only known factor is the noted length of the subject.

    By using common sense and inspecting the photo, approximate values can be assessed for the height above the ground that the photo was taken, the distance to the subject, the angle of the oblique view, and that the subject is essentially a plain flat-sided box.

    As the appearance of the two visible sides both taper away from the viewer one can assume, for this exercise, that the perspective view can be regarded has being arranged with a horizon line through the subject with vanishing points to the left and right.

    With the assessed values and assumed arrangement, one can draw projections back that show where the subject orthogonal plan vertices are located and attempt to position an assumed rectangular plan to suit.
    I suspect one must assume a subject width to get a solution, which in this particular case can be closely estimated by reference to other technical documentation.

    As an aide to checking the viewing point, I think it should be possible to check that the the assumed viewing point does produce the correct tapered views to the two vanishing points.

    Once the first orthogonal solution was obtained, the corresponding perspective sketch can be produced and compared to the original photo.
    A visual inspection should then enable refinement of all the assessed and assumed values and the process repeated to move the solution closer to the correct one.

    This has been a fascinating exercise with multiple pencil sketches on scraps of paper.
    I have obtained a drawing board with a large roll of paper and will attempt to apply the approach described above.

    John.

  8. #7
    Join Date
    May 2013
    Location
    Somerset Region, Qld, AU.
    Age
    66
    Posts
    602

    Default

    Quote Originally Posted by electrosteam View Post
    I have searched the web for a simple description of the Descriptive Geometry projections to convert a perspective photograph into an engineering drawing (3rd angle orthographic).

    There are lots of discussions on the relationships between views, how to draw in perspective with arbitrary assumptions, deep technical texts on multilayered projections and lots of software matrix conversion theory - but no simple procedure that I could find.

    I think I have developed the simple drawing projections to convert an orthographic drawing into a perspective sketch, and I intend to try and work those projections backwards.

    I do not need any references to software routines or fancy photo manipulation programs, just the projections that one could utilize with pencil and ruler on a drawing board.

    Can anyone point me to a suitable source ?
    Is anyone interested in discussing the problem ?

    The particular immediate application for me is a photo of a very old electric narrow-gauge locomotive that I will like to model in 5 inch gauge.

    John.
    John,

    I know that you said that you "do not need any references to software routines", but stay with me, as I believe that some of the techniques that are used to create a working drawing from a series of photographs using a computer drafting programme such as Sketchup, are also transferable to using a drawing board instead of a computer.

    The basic process using the computer program (you substitute your drawing board), is to trace a perspective drawing over the photograph, and then convert the perspective drawing to orthographic projections or whatever projections you need. It sounds simple, but it isn't ! You soon find out how much distortion there is in the photograph when you realise that lines in the photograph that should be straight, are in fact curved in the photo.

    I've done this process a few times now to create plans for reproduction antique furniture. The results are a set of outline drawings that are sufficient to start designing the construction of the reproduction item, and to produce the working drawings.

    There are a few limitations that apply to using this process to get an accurate drawing. I know that you're using a very old photograph, so some of the following limitations are out of your control, but if you know about those limitations, it may help when you're doing the drawing. The most important limitations are:


    1. The photographs need to be taken with the film plane (or digital sensor plane) as near to vertical as possible, and normally, you would record the camera height and camera's distance to a specific point on the object, to help when drawing an accurate perspective view. For example, if the photographer tilted the camera up to get the top of the loco in the photograph, then you'll also have converging verticals to deal with. The opposite errors would be present if the photographer was above the loco (i.e. on an over-bridge) tilting the camera downwards to look at the loco.
    2. You'll get the best results if you can get photographs that are as close to orthographic views as possible. For furniture reproduction, if I am taking the photo myself, I aim to get four views (front, back, and both end views), plus close-up views of detail features.
    3. It is easier to do if the camera lens that was used to take the photograph was a "standard" lens, that is, one that is equivalent to a 50mm lens on a full frame 35mm digital or film camera. If a wide angle or a telephoto lens is used to take the photograph, you will encounter much more perspective distortion - distance shortening with a telephoto lens, and distance expansion with a wide angle lens.
    4. Include a measure in the photographs. When photographing furniture that I want to reproduce, I include two rulers in each photograph. The rulers are placed on the face that I'm photographing; one oriented vertically, and one oriented horizontally. They are used to accurately scale the drawing.


    I've tried to use oblique photographs to produce a set of drawings, and it is much harder. It soon becomes apparent that a camera lens does not produce a true perspective drawing. One technique that you could try to gauge how much perspective error there is in your old photograph, is to use a photocopier to enlarge it to A3- black & white will do. Then sit down at the drawing board and start looking for a combination of horizon lines and vanishing points that work on that photograph. If you're lucky, there will be only a small amount of distortion that you may be able to work around.

    I did one set of drawings of an antique desk. The photographs were a series of oblique views taken from a book published by a Museum in the UK. I wrote to the museum and told them I wanted to build a reproduction, and asked if they had any scaled drawings of any sort for this item. They wrote back that they didn't have any scaled drawings (and asked for a copy of mine when I'd finished them), and instead sent back a series of A3 photographs with lots of accurate measurements marked on the photographs.

    That same approach might work in your case, if there is one of these locos in Museum or Collection somewhere in the world..... If not a loco exactly the same, then maybe a close cousin might provide the key detailed measurements that you'll need to start to produce accurate drawings from your photo. If you're lucky, a museum or collection may even have preserved some original manufacturer's drawings. I remember visiting the Railway Museum in York UK many years ago, and as part of the museum tour was shown their massive collection of manufacturer's drawings for most UK based engine manufacturers, and for many of the overseas subsidiaries of those UK manufacturers.

    Anyway, I hope that info helps. Let us know how you get on, as producing working drawings based on photographs is a near essential process for anyone who wants to build reproductions, wither the reproductions are scale locos or furniture.

    Regards,

    RoyG
    Manufacturer of the Finest Quality Off-Cuts.

  9. #8
    Join Date
    Feb 2003
    Location
    back in Alberta for a while
    Age
    68
    Posts
    12,006

    Default

    Quote Originally Posted by electrosteam View Post
    I do not need any references to software routines or fancy photo manipulation programs, just the projections that one could utilize with pencil and ruler on a drawing board.

    Can anyone point me to a suitable source ?
    Is anyone interested in discussing the problem ?

    The particular immediate application for me is a photo of a very old electric narrow-gauge locomotive that I will like to model in 5 inch gauge.

    John.
    Hi John

    I can't help you much with your first question.
    These days very little drawing is done by hand, lots of sketches, but very few real drawings.
    what I recall from when I learnt to do orthographic drawings, there was no "routines" as such to go from perspective back to orthographic. Students were expected to learn how to go from orthographic to perspective -- reverse engineering perspective into orthographic was reliant on a students "intelligence"


    But your second question ...
    what do you already know about the loco?
    basic dimensions -- length, width, height, gauge ?
    don't assume lines on the original are actually parallel ?

    assuming you want to get your model as close as possible to the original, I'd be approaching the "problem" as an iterative exercise.
    create a set of outline orthographic drawings
    distort that object to match the perspective in the photo -- check for significant differences
    adjust the drawing and try again

    the process is much faster if you work with a solid 3-D computer model, but you don't want to go that route
    regards from Alberta, Canada

    ian

  10. #9
    Join Date
    Jun 1999
    Location
    Westleigh, Sydney
    Age
    77
    Posts
    9,542

    Default

    OK, this may or may not be helpful.
    About 30 years ago, National Geographic carried out an investigation using old photos, to see if Peary had really reached the North Pole. They made some assumptions about height etc., and measured shadow lengths etc. The article gave details of their calculations and methods, which could be helpful.
    If you visit your local doctors surgery, you may find the magazine article and get some help.
    Visit my website
    Website
    Facebook

  11. #10
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    422

    Default

    I have gone silent for the last week doing 'other things' but I have done some projections on paper that soon became a forest of lines, so I thought I would try the CAD as a demonstration of the method.
    The multiple layers and easy erase of the CAD should make the forest controllable.

    But the CAD also has a problem, I immediately ran into the absence of a command to " draw a perpendicular line from a selected point on a line".

    This simple construct is the fundamental basis for the classic ruler, square and pencil on a drawing board.
    I have searched and it appears to be a construct that is not commonly available.

    There are numerous work-arounds, and my current favourite is to construct a rectangle along the line and out to the required distance, then add another line on top of the perpendicular leg, and erase the rectangle.

    Have I missed something ?
    I use DraftSight and LibreCAD.

    Still happily drawing,
    John.

  12. #11
    Join Date
    Oct 2006
    Location
    Tallahassee FL USA
    Age
    82
    Posts
    4,650

    Default

    Quote Originally Posted by electrosteam View Post
    I have gone silent for the last week doing 'other things' but I have done some projections on paper that soon became a forest of lines, so I thought I would try the CAD as a demonstration of the method.
    The multiple layers and easy erase of the CAD should make the forest controllable.

    But the CAD also has a problem, I immediately ran into the absence of a command to " draw a perpendicular line from a selected point on a line".

    This simple construct is the fundamental basis for the classic ruler, square and pencil on a drawing board.
    I have searched and it appears to be a construct that is not commonly available.

    There are numerous work-arounds, and my current favourite is to construct a rectangle along the line and out to the required distance, then add another line on top of the perpendicular leg, and erase the rectangle.

    Have I missed something ?
    I use DraftSight and LibreCAD.

    Still happily drawing,
    John.
    Yes, you have.

    I know of no direct command to draw a line perpendicular from a point. In AutoCAD, I draw a line from anywhere perpendicular to the line (which may end well away from the line, but doesn't matter). Then move the new line to its target location, using its end point as object snap, and the target location as the other.

    Cheers,
    Joe
    Of course truth is stranger than fiction.
    Fiction has to make sense. - Mark Twain

  13. #12
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    422

    Default

    Joe, and then you have to put in an offset from the original line the correct distance out, trim the perpendicular line to length and erase the offset line --- arghhhh !

    I don't think a simple adjustment of properties will work because the start/end of the perpendicular line are the wrong way round.

    It astounds me that this simple construct is not part of the standard CAD armory of tools.

    The subject is of some interest because to draw the perspective from the orthogonal:
    - draw Ray1 from the vanishing point through a selected point to the picture plane,
    - draw Perpendicular1 to Ray1 at the point with a length the height of that point above/below the horizontal line,
    - draw Perpendicular2 where the Ray1 meets the PP
    - draw Ray2 from the VP through the end of Perpendicular1 intersecting Perpendicular2,
    - trim Perpendicular2 at the intersection with Ray2,
    - rotate Perpendular2 until it is perpendicular to the PP, above or below as appropriate for the selected point,
    - the end of the rotated Perpendicular2 now represents the perspective view of the selected point,
    - erase all the constructed lines.

    Note the rotation requirement gets back to constructing a perpendicular.

    The above construction simply scales the size of the viewed perspective, the size is varied by moving the picture plane closer or further away from the vanishing point.

    I have swapped a forest of lines on the paper for multiple keystrokes on the CAD, not sure which is more time consuming and subject to error.

    John.

  14. #13
    Join Date
    Feb 2003
    Location
    back in Alberta for a while
    Age
    68
    Posts
    12,006

    Default

    in the drawing software I normally use -- a true vertical or horizontal line is drawn by selecting the line tool, clicking on the originating edge and holding the CTRL key while you drag your vertical or horizontal line.

    Also, I can put the "forest of lines" into a separate layer


    This case was drawn that way

    Lesley's carry case 2.jpg
    regards from Alberta, Canada

    ian

  15. #14
    Mobyturns's Avatar
    Mobyturns is offline In An Instant Your Life Can Change Forever
    Join Date
    Jul 2012
    Location
    "Brownsville" Nth QLD
    Age
    66
    Posts
    4,411

    Default

    Quote Originally Posted by joe greiner View Post
    Yes, you have.

    I know of no direct command to draw a line perpendicular from a point. In AutoCAD, I draw a line from anywhere perpendicular to the line (which may end well away from the line, but doesn't matter). Then move the new line to its target location, using its end point as object snap, and the target location as the other.

    Cheers,
    Joe
    Copy the line you want to draw perpendicular too.

    Rotate the copy 90 degrees.

    Make further copies of the rotated line and paste them using object snaps (osnaps) to snap "near" or onto a "node" etc.

    Commands & features will vary across CAD packages. In AutoCAD you can use the temporary tracking snaps to create virtual construction lines.

    http://www.cadtutor.net/forum/showth...ndicular-lines

    http://www.cadtutor.net/tutorials/au...bject-snap.php
    Mobyturns

    In An Instant Your Life CanChange Forever

  16. #15
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    422

    Default

    Guys,
    First off I apologize for dragging the topic into CAD, but, I will persevere with my initial interest in understanding the projections necessary to accomplish the task.

    Ian,
    I don't quite understand your method, what CAD package are you using ?

    Mobyturns,
    That's a brilliant suggestion, I will be trying it this morning.
    I am thinking it may be possible to nominate the length as the line is drawn, so a minimum of keystrokes.

    John.

Page 1 of 3 123 LastLast

Similar Threads

  1. Ink drawing
    By Andy Mac in forum ART
    Replies: 5
    Last Post: 20th October 2017, 05:18 PM
  2. Tech drawing without a drawing board
    By DaveTTC in forum WOODWORK - GENERAL
    Replies: 10
    Last Post: 26th June 2015, 06:19 PM
  3. Drawing Aid
    By Chris Parks in forum DESIGN & DESIGNING / GOOGLE SKETCHUP
    Replies: 7
    Last Post: 12th May 2013, 09:29 PM
  4. 3D drawing
    By stevo81 in forum CNC Machines
    Replies: 14
    Last Post: 5th April 2012, 10:08 AM
  5. drawing curves
    By Redback in forum WOODWORK - GENERAL
    Replies: 8
    Last Post: 27th May 2005, 10:51 AM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •