Re: Wall Declination Measurement
Dear Alex, Thank you for your rapid reply... > As architect my comment on no.1. is that the north arrow which > we place in drawings (at least the ones I place) are based on > the North direction on large scale survey maps supplied by > planning authorities and on which the drawing would be based. That certainly makes sense. Here in the U.K. we would have to know whether the large scale map used true north or grid north but, subject to that caveat, your arrow ought to be within a degree or two of being right. The main reason for errors of 15 degrees or so seems to be a result of modern surveying practice using instruments which measure distance as well as angle... What seems to happen is that the surveyor takes ONE primary point on a building site and marks this on the ground with a pin and a little circle. This is the origin of an x,y,z coordinate system in which positive z is vertically up and the x-y plane is horizontal. This still lacks an orientation. In theory, positive y is due north and positive x is due east. Surveyors don't actually use the letters x, y, and z but talk about Easting, Northing and Height respectively. I have watched these guys at work. When they start off, they choose a reference origin quite carefully (you don't want a spot which is going to be built over or have huts on it) but they are much less fussy about orientation. They will simply guess which way is north (or east if that is more convenient) and slap a target on a wall and use that as their reference orientation for the whole construction period. If it is 15 degrees out no one seems to mind! Maybe surveying practice is more rigorous in Malta! Frank -
Re: Wall Declination Measurement
Dear Mr King, Interesting post. As architect my comment on no.1. is that the north arrow which we place in drawings (at least the ones I place) are based on the North direction on large scale survey maps supplied by planning authorities and on which the drawing would be based. Errors of 15 degrees are quite serious in this respect, even though one should always take the arrow only as a general indication of north and not for accurate sundial work, for which I would favour four trials (a few days apart) of Waugh's technique from his book. Best regards Alex Malta 1. Architect's Drawings A typical Architect's site plan includes a very convincing ornamented letter N enfolding an arrow. The arrow usually points at some arbitrary angle with respect to the sides of the paper. Alas, the angle is also pretty arbitrary with respect to true north. I have known errors up to 15 degrees. Verdict: Avoid like the plague
Re: Wall Declination Measurement
I have been enjoying the comments on estimating wall declination, especially those which have the ring of experience about them. I am prompted to offer the following Consumer Guide to the methods I have used over the years (and two I haven't). I am sure that many readers will be able to add to my list: 1. Architect's Drawings A typical Architect's site plan includes a very convincing ornamented letter N enfolding an arrow. The arrow usually points at some arbitrary angle with respect to the sides of the paper. Alas, the angle is also pretty arbitrary with respect to true north. I have known errors up to 15 degrees. Verdict: Avoid like the plague 2. Large-Scale Maps Good maps may well stem from very careful surveys but the representations of buildings are often more suggestive than accurate. You can often determine latitude and longitude to high precision but should treat the orientation of a depicted wall with great caution. You also have to worry (in the U.K.) about distinguishing grid north from true north. Verdict: Avoid 3. Magnetic compass Subject to numerous caveats you ought to be able to get good results. You have to be sure that there isn't a hidden iron drain or some such nearby and, of course, you need to know the local magnetic variation. The method is no use if the magnetic dip is too large. Verdict: Avoid 4. Using Solar Azimuth - General Carol Arnold, John Davies, Tony Moss and Bill Gottesman have described variants of the same idea: use the sun! I have used all these and more. I am not keen on plumb lines [they don't keep still and if you use a bucket of water to dampen the swings you just get a bowed string!]. If you make many observations widely spaced in hour-angle you can get a result better than 10 arc-minutes. Verdict: Fair to Good 5. Using Solar Azimuth - Window Ledge Method If you simply place a sheet of paper on a window ledge with one edge firmly against the inside of the bottom of the window frame you can often get the vertical edge of the window frame or a vertical glazing bar to cast a shadow. You draw a line just ahead of the (moving) shadow and note the time that the shadow reaches the line. Typical window ledges are close to horizontal and the sides of windows are approximately vertical so this can be quite accurate. Verdict: Fair 6. Using Solar Azimuth - Letting the client do it What do you do if you have to rely on someone else? The instructions I have given overseas clients (for example) are as follows: Find a flat board, a sheet of squared paper, a spirit level, a wooden pencil and a digital clock (preferably one that is radio-controlled and shows the date as well as the time). Place the board against the wall and place the squared paper on the board with one edge against the wall. Place the clock on the piece of paper. Check that the board is level and stand a pencil so that it balances on its blunt end (this is an added check that the board is level). Arrange that the pencil casts a shadow that falls across the squared paper. Take several digital photographs (preferably over several hours) which show the paper, the pencil, the shadow and the clock. E-mail me the results the same day. By counting squares I can get a reasonable estimate of the angle the shadow makes to the wall. The rest is as for 4 and 5. Make sure that you know how the time on the clock relates to UTC. Verdict: Fine if there is no other way 6. Using GPS An up-market approach using GPS kit exploits two GPS receivers each slaved to the other so that the relative phase-angles of the signals received from each satellite can be compared. You let the system run for 6 hours or so and via a good deal of software you can determine the position or one receiver relative to the other to about 5mm. Their absolute positions will not be known to such precision but that doesn't matter. Using a 50m baseline, a 5mm error means you can determine the azimuth of the baseline to about 20 arc-seconds. You then use standard surveying techniques to find the declination of your wall. You have to take care not to get stray reflections so you should be high up on something solid. Scaffolding will not do! This works splendidly even if it is cloudy. The snag is the cost. The kit costs about $80,000 and is obviously expensive to hire. It is suitable for high-budget sundials only! Verdict: Wonderful if you have a rich client 7. Cassini Method When setting out camera obscura noon marks a technique, which I think is due to Cassini, is first to note the point on the floor perpendicularly below the hole in the roof (immensely difficult to determine accurately) and then draw concentric circles round that point. Next you plot the hyperbolic path followed by the
Re: Wall Declination Measurement
I've got that drawing of your somewhere but I can't locate it. Could you please send me a copy? thanks John - Original Message - From: "tony moss" <[EMAIL PROTECTED]> Cc: "Sundial List" Sent: Monday, November 29, 2004 9:46 AM Subject: Re: Wall Declination Measurement John Carmichael wrote: Subject: Wall Declination Measurement Hopefully, somebody from the sundial list will help us. This is my own preferred method of determining wall declination but, before originally adopting it, I needed to be sure that a) the 'nail' was truly pependicular to the measuring board and b) the plumbline/pencil line ran exactly through the axis of the nail. Without this certainty the results might be questionable so to that end I developed my 'precision declinometer' which I know has been adopted in various forms by other diallists. It uses a tapered 'gnomon' spike sliding in a machined vee groove*. The novel idea was to include a needle point in the butt end of the spike which punctures the recording paper exactly on its axis. For anyone who missed the previous offer via this list some years ago I can supply a gif and jpeg showing how it is made and used. Like John Davis I also prefer to take a number of readings over an extended period then take an average. * An accurately drill hole is almost as good but 'drilling is the least precise process in engineering' and unless a good sliding fit is obtained then the tip and needle point can wobble off centre whereas a vee groove constrains the spike precisely in two perpendicular planes. Tony Moss - -
Re: Wall Declination Measurement
I wrote a program that determines declination of a vertical wall using just a watch and a carpenter's square. It gives very accurate results if performed when the square's shadow is long. Be certain to follow directions closely, and measure the edge of the shadow as described in the method. Take a few measurements for consistency. Download it free at www.precisionsundials.com/walldeclination.exe Bill G. -
Re: Wall Declination Measurement
John Carmichael wrote: >Subject: Wall Declination Measurement >Hopefully, somebody from the sundial list will help us. This is my own preferred method of determining wall declination but, before originally adopting it, I needed to be sure that a) the 'nail' was truly pependicular to the measuring board and b) the plumbline/pencil line ran exactly through the axis of the nail. Without this certainty the results might be questionable so to that end I developed my 'precision declinometer' which I know has been adopted in various forms by other diallists. It uses a tapered 'gnomon' spike sliding in a machined vee groove*. The novel idea was to include a needle point in the butt end of the spike which punctures the recording paper exactly on its axis. For anyone who missed the previous offer via this list some years ago I can supply a gif and jpeg showing how it is made and used. Like John Davis I also prefer to take a number of readings over an extended period then take an average. * An accurately drill hole is almost as good but 'drilling is the least precise process in engineering' and unless a good sliding fit is obtained then the tip and needle point can wobble off centre whereas a vee groove constrains the spike precisely in two perpendicular planes. Tony Moss -
Re: Wall Declination Measurement
Gianna got in before me with the answer to your question. I use a version of the "nail in a board" method myself. I like to take several measurements, preferably over a couple of hours, to improve the accuracy of the measurement. As well as the horizontal position, I also record the vertical position of the shadow tip below the base ot the "nail". This can be compared with the sun's altitude and proves a useful double-check, allowing doubtful readings to be discarded. Regards, John --John Carmichael <[EMAIL PROTECTED]> wrote: Hello Carol: (c.c Sundial List) I'm back home and this morning I'm looking at your wall declination measurements. Unfortunately, I am not accustomed to using the nail method you used and I hesitate to comment because I don't want to make a mistake. I have heard of this method however. I am going to forward your letter to our Sundial List discussion group and hopefully somebody there will be able to check your measurements. But I was able to check your solar azimuth data that you got from your astronomy program. According to the program I use (The Dialist Companion), the solar azimuth at that latitude, longitude and time was about 20.45 degrees west of south, not 209 degrees. Just think about it. If the solar declination were 180 degrees west of south, the sun would be due north and that's not possible. 209 degrees would be towards the North East which is also impossible. Hopefully, somebody from the sundial list will help us. John - Original Message - From: carol arnold To: John Carmichael Sent: Monday, November 22, 2004 1:09 PM Subject: declination John, I was just having a go at measuring the declination of a window in my house - I am not convinced of the accuracy of my measurement of sun angle to wall,but I wondered if you could double check the calcualtions? The window was approx south facing. 22 nov 2004 at14.01 gmt I used a nail 92mm long on a vertical board and its shadow was 50mm to the right of the nail. So the sun angle to the wall is 28 deg 31min 23sec west of south. My astronomy program gave me azimuth of sun to be 209 deg 44min 31sec ie 29deg 44min 31sec west of south, for lat 51deg 25min 20sec North and long 2 deg 42 min 30 sec west. So I reckon the the wall faces 1 deg 13 min 8 sec west of south?? Regards and hope you dont mind my asking you about this, Carol Carol Arnold Stained glass artist, commissions welcome, please take a look at my stained glass website http://www.carolarnold.co.uk Moving house? Beach bar in Thailand? New Wardrobe? Win £10k with Yahoo! Mail to make your dream a reality.Dr J R DavisFlowton DialsN52d 08m: E1d 05m
Re: Wall Declination Measurement
I think the measurement of the wall declination with the nail method done by Caroil is correct. The azimuth of the sun is 29deg 44min 31sec west of south on the mentioned place and time. And thus the wall declination is: 29deg 44min 31sec - 28 deg 31min 23sec = 1 deg 13 min 8 sec west of south Willy Leenders Hasselt, Flanders in Belgium John Carmichael wrote: Hello Carol: (c.c Sundial List) I'm back home and this morning I'm looking at your wall declination measurements. Unfortunately, I am not accustomed to using the nail method you used and I hesitate to comment because I don't want to make a mistake. I have heard of this method however. I am going to forward your letter to our Sundial List discussion group and hopefully somebody there will be able to check your measurements. But I was able to check your solar azimuth data that you got from your astronomy program. According to the program I use (The Dialist Companion), the solar azimuth at that latitude, longitude and time was about 20.45 degrees west of south, not 209 degrees. Just think about it. If the solar declination were 180 degrees west of south, the sun would be due north and that's not possible. 209 degrees would be towards the North East which is also impossible. Hopefully, somebody from the sundial list will help us. John - Original Message - From: carol arnold To: John Carmichael Sent: Monday, November 22, 2004 1:09 PM Subject: declination John, I was just having a go at measuring the declination of a window in my house - I am not convinced of the accuracy of my measurement of sun angle to wall,but I wondered if you could double check the calcualtions? The window was approx south facing. 22 nov 2004 at14.01 gmtI used a nail 92mm long on a vertical board and its shadow was 50mm to the right of the nail. So the sun angle to the wall is 28 deg 31min 23sec west of south.My astronomy program gave me azimuth of sun to be 209 deg 44min 31sec ie 29deg 44min 31sec west of south, for lat 51deg 25min 20sec North and long 2 deg 42 min 30 sec west.So I reckon the the wall faces 1 deg 13 min 8 sec west of south?? Regards and hope you dont mind my asking you about this,Carol Carol ArnoldStained glass artist, commissions welcome,please take a look at my stained glass website http://www.carolarnold.co.uk Moving house? Beach bar in Thailand? New Wardrobe? Win £10k with Yahoo! Mail to make your dream a reality.
Re: Wall Declination Measurement
Hello John , the values written by Carol are all correct and very accurate and her wall faces exactly 1 deg 13 8 west of south In astronomy the azimuth values start from north and therefore a value of 209 deg corresponds, for the dialist, to 29 degs from South toward West. Regards Gianni Ferrari 44° 39' N 10° 55' EMailto : [EMAIL PROTECTED] - Original Message - From: John Carmichael To: carol arnold Cc: Sundial List Sent: Monday, November 29, 2004 2:55 PM Subject: Wall Declination Measurement Hello Carol: (c.c Sundial List) I'm back home and this morning I'm looking at your wall declination measurements. Unfortunately, I am not accustomed to using the nail method you used and I hesitate to comment because I don't want to make a mistake. I have heard of this method however. I am going to forward your letter to our Sundial List discussion group and hopefully somebody there will be able to check your measurements. But I was able to check your solar azimuth data that you got from your astronomy program. According to the program I use (The Dialist Companion), the solar azimuth at that latitude, longitude and time was about 20.45 degrees west of south, not 209 degrees. Just think about it. If the solar declination were 180 degrees west of south, the sun would be due north and that's not possible. 209 degrees would be towards the North East which is also impossible. Hopefully, somebody from the sundial list will help us. John - Original Message - From: carol arnold To: John Carmichael Sent: Monday, November 22, 2004 1:09 PM Subject: declination John, I was just having a go at measuring the declination of a window in my house - I am not convinced of the accuracy of my measurement of sun angle to wall,but I wondered if you could double check the calcualtions? The window was approx south facing. 22 nov 2004 at14.01 gmt I used a nail 92mm long on a vertical board and its shadow was 50mm to the right of the nail. So the sun angle to the wall is 28 deg 31min 23sec west of south. My astronomy program gave me azimuth of sun to be 209 deg 44min 31sec ie 29deg 44min 31sec west of south, for lat 51deg 25min 20sec North and long 2 deg 42 min 30 sec west. So I reckon the the wall faces 1 deg 13 min 8 sec west of south?? Regards and hope you dont mind my asking you about this, Carol Carol Arnold Stained glass artist, commissions welcome, please take a look at my stained glass website http://www.carolarnold.co.uk Moving house? Beach bar in Thailand? New Wardrobe? Win £10k with Yahoo! Mail to make your dream a reality.
Wall Declination Measurement
Hello Carol: (c.c Sundial List) I'm back home and this morning I'm looking at your wall declination measurements. Unfortunately, I am not accustomed to using the nail method you used and I hesitate to comment because I don't want to make a mistake. I have heard of this method however. I am going to forward your letter to our Sundial List discussion group and hopefully somebody there will be able to check your measurements. But I was able to check your solar azimuth data that you got from your astronomy program. According to the program I use (The Dialist Companion), the solar azimuth at that latitude, longitude and time was about 20.45 degrees west of south, not 209 degrees. Just think about it. If the solar declination were 180 degrees west of south, the sun would be due north and that's not possible. 209 degrees would be towards the North East which is also impossible. Hopefully, somebody from the sundial list will help us. John - Original Message - From: carol arnold To: John Carmichael Sent: Monday, November 22, 2004 1:09 PM Subject: declination John, I was just having a go at measuring the declination of a window in my house - I am not convinced of the accuracy of my measurement of sun angle to wall,but I wondered if you could double check the calcualtions? The window was approx south facing. 22 nov 2004 at14.01 gmt I used a nail 92mm long on a vertical board and its shadow was 50mm to the right of the nail. So the sun angle to the wall is 28 deg 31min 23sec west of south. My astronomy program gave me azimuth of sun to be 209 deg 44min 31sec ie 29deg 44min 31sec west of south, for lat 51deg 25min 20sec North and long 2 deg 42 min 30 sec west. So I reckon the the wall faces 1 deg 13 min 8 sec west of south?? Regards and hope you dont mind my asking you about this, Carol Carol Arnold Stained glass artist, commissions welcome, please take a look at my stained glass website http://www.carolarnold.co.uk Moving house? Beach bar in Thailand? New Wardrobe? Win £10k with Yahoo! Mail to make your dream a reality.
