Help making scaled plan

M

Michelle N

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Joined
Oct 31, 2019
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7
Hi,
I'm really hoping someone can help me. I've been trying to make a plan of an area of my yard so I can use it to make a design for a new garden. I decided that the easiest way to convert for scale is to measure in inches and draw in the equivalent number of millimeters on my software (i.e. 1mm = 1 inch). I have a border on one side that is an existing patio and three existing shrubs plus an electrical outlet. What I did was take one straight edge of the patio and measured it as the base of a triangle (|AB = 70 inches). I then measured (using a laser, so accurate enough for my purposes) from point A to the centre of each shrub and also the outlet, and did the same from point B to each. I thought that all I would have to do would be to use each measurement as a radius of a circle with centre points at A and B and where they intersected would be the position of the shrub/outlet in question. (So for example |AC was 14 feet, 11 inches, |BC 12 feet, 9 inches; my drawn circle centred on A was 358mm in diameter, my circle centred on B had a diameter of 306mm). However, this resulted in a picture where instead of shrubs E and F being next to each other as in real life and in the rough sketch below, they ended up almost on top of each other. I must be doing something wrong but I don't know if it's my measurement, my arithmetic, my scaling, or my geometry.
My measurements were as follows:
|AB = 5' 10"
|AC = 14' 11"
|BC = 12' 9"
|AD = 11' 1"
|BD = 7' 3"
|AE = 16'
|BE = 10' 11"
|AF = 15'
|BF = 9' 11"
window outlook sketch.jpg
 
I'd want to see your result, not just your sketch of what it should be, in order to decide what you might be doing wrong.

But it looks like it might be the measurements. Here is my drawing in GeoGebra (which I made without looking at your sketch, so it's backward).

FMH118850.png
 
Would you want to see the circles included or just the resulting positions of my objects?

I'm looking at your drawing and I just can't see how the measurements I did could result in a picture that is so out of sync with the actual stuff on the ground. I originally did my measurements with a tape measure but when things looked off, I decided to get a laser measuring tool. Since I was on uneven ground etc. I figure I might have a couple of inches of error give or take, but not so much that everything would be completely out of whack. Would the angle of |AB make a difference that would account for it? To my eye it looks about 45 degrees so that's what I used in my drawing.

I just looked through my photos but I don't have one since bushes E & F were planted, so I'm afraid I can't show you what it really looks like.
 
If I were you, I'd go out and try to manually measure the distances to E and F. Do you see that your distances to them, from both A and B, differ by 1 foot? That puts them about 1 foot apart, which clearly is not what you expect. I suspect you accidentally measured the wrong distances, perhaps something other than the center of each object.

My picture is reflected left to right from yours, because I went in the wrong direction. Here is a corrected copy. The orientation of AB is irrelevant apart from making the pictures match up.

FMH118850 a.png
 
Michelle N said:
Hi,
I'm really hoping someone can help me. I've been trying to make a plan of an area of my yard so I can use it to make a design for a new garden. I decided that the easiest way to convert for scale is to measure in inches and draw in the equivalent number of millimeters on my software (i.e. 1mm = 1 inch). I have a border on one side that is an existing patio and three existing shrubs plus an electrical outlet. What I did was take one straight edge of the patio and measured it as the base of a triangle (|AB = 70 inches). I then measured (using a laser, so accurate enough for my purposes) from point A to the centre of each shrub and also the outlet, and did the same from point B to each. I thought that all I would have to do would be to use each measurement as a radius of a circle with centre points at A and B and where they intersected would be the position of the shrub/outlet in question. (So for example |AC was 14 feet, 11 inches, |BC 12 feet, 9 inches; my drawn circle centred on A was 358mm in diameter, my circle centred on B had a diameter of 306mm). However, this resulted in a picture where instead of shrubs E and F being next to each other as in real life and in the rough sketch below, they ended up almost on top of each other. I must be doing something wrong but I don't know if it's my measurement, my arithmetic, my scaling, or my geometry.
My measurements were as follows:
|AB = 5' 10"
|AC = 14' 11"
|BC = 12' 9"
|AD = 11' 1"
|BD = 7' 3"
|AE = 16'
|BE = 10' 11"
|AF = 15'
|BF = 9' 11"
Click to expand...
I think because of the choice of A and B a small error in measurements results in a large difference in location.
For B pick the end point of the patio edge (top left) and try again.
 
@ Dr. Peterson E and F are probably about 45-50 inches apart (on centre), but E is to the right of F, nearly as far as D when looking at it from the patio. I could understand some error creeping in despite my use of a laser (uneven ground, target perhaps not corresponding exactly to the centre of the plant etc.), but I'm surprised that it would make my results so off.
@ lev888 I'll give it a try remeasuring from the corner of the patio (it might not work out very well because that's also at the corner of the house so there's not a lot of room for me to set up the rig for the laser....I'll have to give it some thought). The other corner is not really good either because there's a post to an upper deck there.

Given that you're both pinpointing the measurements as the likely reason for the discrepancy, am I right in assuming that my math and procedure are correct?
 
Thinking about the issue some more, I'm concerned about using the far end of the patio as a reference point for another reason. As you can see, it's a curve, but it's not a true arc. The person who originally laid it down must have done it by eye so it's very irregular. The result is that my drawing of the curve is only a rough approximation--good enough for my eventual purpose of designing my garden bed, but I'm afraid it might introduce even more error into my plan if I try to use it as a point to measure from. The AB line is a straight edge (when I did my original measurement by hand & tape measure, I got 5' 9", only an inch difference from the laser measurement).

This is proving to be a much more difficult problem than I expected.

Just FYI, I've attached two photos of the ground, one from the upper deck shortly after D was planted (you can see the electrical outlet C half-circled on the right edge), one from the opposite angle looking back towards the patio not long after E & F were planted. I'd have taken a current photo today but I didn't get a chance.
20190824_134954.jpg IMG_20190903_150322_cropped.jpg
 
Michelle N said:
@ Dr. Peterson E and F are probably about 45-50 inches apart (on centre), but E is to the right of F, nearly as far as D when looking at it from the patio. I could understand some error creeping in despite my use of a laser (uneven ground, target perhaps not corresponding exactly to the centre of the plant etc.), but I'm surprised that it would make my results so off.
@ lev888 I'll give it a try remeasuring from the corner of the patio (it might not work out very well because that's also at the corner of the house so there's not a lot of room for me to set up the rig for the laser....I'll have to give it some thought). The other corner is not really good either because there's a post to an upper deck there.

Given that you're both pinpointing the measurements as the likely reason for the discrepancy, am I right in assuming that my math and procedure are correct?
Click to expand...
Find a rope or a long extension cord. Attach it to A. Extend it so it makes a right angle with AB. Mark the alternative point B on it at a known distance from A. Use it instead of B.
 
The important thing here is that trilateration (locating an object by its distances from two points) is most accurate when the lines being measured are close to perpendicular, and least when they are nearly collinear. So any baseline you can use such that all your points are off to the side will work better.

All that matters about the baseline is that it be measured accurately (and the other points can be seen from both ends). Not being straight doesn't matter (apart from your ability to draw it well enough for your purposes).

Another possibility, of course, is that you could use triangulation (measuring angles rather than, or in addition to, distances).
 
Thanks both of you for your help. I'll try your suggestion about creating a new point to measure from at a right angle to AB when the weather next cooperates. Presumably that should work better. I'll let you know how it turns out.
 
Yay! Thanks so much for your help!! I made a new point at a right angle to AB to measure from (let's call that G), about 24 feet into the yard and tried again. This time my result looks much closer to my sketch of real life, so I think that worked pretty well (though I'm sure with better tools I could have been more accurate). Visual perspective is a very funny thing. Looking at my objects from any given angle gives a much different impression of where things are situated in relation to each other than this overhead diagram. For example, the picture I posted above of the hydrangeas (E & F) makes it seem as though the rose (D) is right in the middle from left to right, but in reality they are shifted pretty far toward the house by comparison. I must have taken that photo at a similar angle to my original AB line.

In case you're curious, my new measurements from G:
|AG = 23' 11"
|CG = 13' 11"
|DG = 20' 9"
|EG = 20' 11"
|FG = 24' 5"

window outlook screencap 2.PNG
 
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