Dale Posted April 21, 2015 Share Posted April 21, 2015 Hi folks, Can any one refresh my memory with some maths help? I want to work out the scale of a drawing or photo from a given measurement within it. Lets say its a terrace house and I am taking the door height as 6'6". I print the picture off and measure the actual distance on the printed picture of the door as 22mm. What I want to do now is from this information, be able to establish the scale of my picture to measure the other dimensions. How on earth do I do this? I am sure there is a straight forward 'divide x from y' but I really cat remember it. I know you can count brick courses but that's only applicable when looking at a building where standard bricks have been used so I need to be able to amply the scale question to other photo's. Many thanks folks. D. Link to post Share on other sites More sharing options...
buffalo Posted April 21, 2015 Share Posted April 21, 2015 In your example, divide the measured door height in mm by full size height in feet, i.e.22/6.5. This gives 3.3846... or, roughly 3.4. This then gives 3.4mm to one foot. Nick Link to post Share on other sites More sharing options...
david.hill64 Posted April 21, 2015 Share Posted April 21, 2015 In your example, divide the measured door height in mm by full size height in feet, i.e.22/6.5. This gives 3.3846... or, roughly 3.4. This then gives 3.4mm to one foot. Nick Agreed. If you want to keep it all in one set of units then 6'6" is 1981.2mm. So if the photo shows the door to be 22mm, then the scale is 22/1981.2= 90 to 1 (1mm on the photo is 90mm in reality.) But: be careful about parallax effects on tall buildings. If the camera is looking up then the top of the building will appear to be narrower than the base. Not a problem for side on shots of normal buildings. Link to post Share on other sites More sharing options...
Poor Old Bruce Posted April 21, 2015 Share Posted April 21, 2015 Once you have established the nominal size of the door, can you not then move on to counting bricks? It would only apply to one building at a time as, as you say, brick sizes vary over time. Most bricklaying would be plus or minus a bit anyway so whether you end up at 3.8 or 4.2 mm to the foot wouldn't make that much difference. You could always err on the smaller size. Link to post Share on other sites More sharing options...
BG John Posted April 21, 2015 Share Posted April 21, 2015 Don't forget that door sizes vary. Depending on the age, and possibly location, of the houses, they may be less than 6ft 6in. I know these things, as being 6ft 2in and a bit, I learned to duck when going through doorways when house hunting!!! Link to post Share on other sites More sharing options...
Broadway Clive Posted April 21, 2015 Share Posted April 21, 2015 I feel your pain after scribbling sums on scraps of paper on too many occasions myself! So here is a spreadsheet with three tools I designed that may be of use. I've entered some sample figures for your door as examples. The coloured areas should not be written over as they contain the formulae. Model scaling tool.xls Link to post Share on other sites More sharing options...
Dale Posted April 22, 2015 Author Share Posted April 22, 2015 Thanks a lot for the replies folks, much appreciated. D. Link to post Share on other sites More sharing options...
Dale Posted April 22, 2015 Author Share Posted April 22, 2015 Agreed. If you want to keep it all in one set of units then 6'6" is 1981.2mm. So if the photo shows the door to be 22mm, then the scale is 22/1981.2= 90 to 1 (1mm on the photo is 90mm in reality.) But: be careful about parallax effects on tall buildings. If the camera is looking up then the top of the building will appear to be narrower than the base. Not a problem for side on shots of normal buildings. Hi David. Keeping things in mm seems to make sense to me but when i tried 22/1981.2 i ended up with 0.0111055 and so on so how did you get the 90:1 ratio? Dale. Link to post Share on other sites More sharing options...
RMweb Gold stovepipe Posted April 22, 2015 RMweb Gold Share Posted April 22, 2015 1 divided by 0.0111055 is 90, more or less, as is 1981.2 divided by 22. 90 of real dimension for 1 of scale dimension. Link to post Share on other sites More sharing options...
david.hill64 Posted April 23, 2015 Share Posted April 23, 2015 Hi David. Keeping things in mm seems to make sense to me but when i tried 22/1981.2 i ended up with 0.0111055 and so on so how did you get the 90:1 ratio? Dale. As Stovepipe says it is actually 1981.2/22 = 90. Sorry for the confusion: I was just following the mental set 6'6" real life = 22mm photo, therefore 1981.2 real life = 22 mm photo. Therefore 1mm photo = 1981.2/22 real life or about 1:90. The inverse of this is 0.0111055 Link to post Share on other sites More sharing options...
Dale Posted April 23, 2015 Author Share Posted April 23, 2015 Thanks again folks, massive help. I can start to make some scale drawings from all the pictures I have collected. D. Link to post Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.