Definition

1. An indicator or a sighting apparatus on a plane table, used in angular measurement.
2. A topographic surveying and mapping instrument used for determining directions, consisting of a telescope and attached parts.

There are a number of common usage's, the main subject of this web page is the map making surveying instrument used on a table that has been leveled.  On ships an Alidade is used to measure the angle from the ship's longitudinal axis to some target or targets, typically to help determine the ships position relative to the target(s).  Large telescopes have an alidade system that's used to point in azimuth.

These were used on a wooden table that had a drawing attached.  The idea was to make a map while in the field using stadia for distance to the rod.

Development

• The very early Alidades were just a ruler with sighting wires held in a frame at each end.  That was what wasused on the Sketch Boards.  See the 1800s Brass and Army units below.
• A compass can be used as an Alidade when a scale is aligned with the North position.  The Dietzgen Compass with square scale is in this catagory and you can get a scale base for some models of the Brunton Com-Pro pocket transits.
• The K&E Early 1800s Alidade appears to be a transit instrument with a verticle angle measuring vernier capability and probably with stadia hairs in the scope so that distance can be manually computed for inclined shots.  No compass as part of the Alidade.

The Berger T-778, Gurley, K&E 5187A, K&E 53491, Lutz, Ottway Ealing No 92, San appear to be this type.
• The Dietzgen 6220 & 6230 added a stadia computation scale "Beaman Stadia Arc" to the vernier making it much easier to compute the distance to the target.

The early Dietzgen seems to also have this capability.  TM 5-6675-211-15P for the Dietzgen 6220 & 6230 has change 2 dated 23 May 1973.
• A number of the newer K&E Alidades use an optical scale like in a theodolite.  Optical scales inserase the accuracy of measured angles as compared to reading a vernier.  The Watts and Wild Alidades may use optical scales.
• The K&E 76 0000 adds what they call "self indexing".  This is an auto level function where the optical path is leveled by a pendulum when the bubble is within the outer ring of the level vial.  The reason for this is to save a huge amount of time when compared to older systems that need to have the table leveled for each shot.  This means that the table does not need to be accurately leveled.  This can be a problem if the Alidade is moved after the sight and before a reading.
• Alidades were probably replaced by total stations since they can determine azimuth, elevation and distance all automatically, the latest versions work without retro reflection prisims on most targets.

In this close up photo of the K&E 5093A Scale you can see that when the alidade is level the Lower center vernier will read 30 degrees, not zero.  This is to avoid blunders which probably were common if level was 0 and there were + and -  numbers on both sides of 0 where a sign error would be a blunder.  Vertical angles from -30 deg to +30 deg can be read as 0 to 60 deg.  That is the limit of vertical angle measurements, since the rest of the scale is used for the horizontal and vertical distance factors.

On the left is the "HOR" vernier and on the right the "VERT" vernier.  These are used to convert the slant distance measured using the stadia method into horizontal and vertical distances.  When the alidade is level the HOR correction reads 100% and the vertical correction reads 50% (note you need to subtract 50 from the VERT reading to get the correction factor that's multiplied times the slant distance.

Notice that when the alidade is level all three readings are very much different.  Again, I'm sure this is to aviod blunders.

Links

plane table surveying - is a good search phrase

Article in Point Of Beginning "Plane Table Mapping" -
Penmap Digital Plane Table -
Instruments of Science and Technology - The Plane Table -
Doug's Amateur Surveying Page - links to some plane table references
Elements of surveying and surveying equipment - Ch 11 -   Plane Table -
Comparison of surveying techniques -
Surveyor's Plane Table - offered new for sale in the UK, and a very simple alidade.
F.W. Breithaupt & Sohn - Topographical Instruments -
Surveying Historical people & dates -

Ebay

This is a collection of Alidade surveying  instruments from eBay.

1800s Brass

eBay -

Army

eBay

Berger

T-778
eBay reserve not met, relisted  eBay

1951.C.T.I MFG CO.LTD.

eBay

Dietzgen

Might have stadia computation on vernier?
eBay

Compass with square scale
eBay
eBay

6220 (12 to 24 Power) & 6230 (10 to 18 Power)

no photo yet

Gurley

Cat. No. 508  has "H" scale
.  18x24" w/Johnson tripod head  eBay

eBay

eBay

Teledyne Gurley No. 582
.  The has "H" & "V" Scales, eBay -

Teledyne Gurley No. 582
eBay
 

K&E

Alidades

Models with the suffix "SA" have a stadia arc.

Tripods

Three versions:
5096A - 11 3/4# rigid
5096B - 14 # rigid
5096C - 9# extension legs

Drawing Boards

5096-1 is 15" x 15"
5096-2 is 18" x 18"
5096-3 is 18" x 24"
5096-4 is ?
5096-5 is 24" x 31"

Mk II non optical Alidade

1800 or early 1900s
eBay
5187A
eBay

No. 5093A called the Geological Survey Alidade weight 7#
eBay

No 5095A called the Expedition Alidade (more compact design), weight 5 #
eBay

63886  1935
eBay - photob, photoc, photod, photoe  -

199892
eBayeBay
119029 might be a model 76 0030
eBay

Military model
eBay -

eBay, eBay
Model: 5093A eBay
 

   Model 53491 eBay

K&E 76-0000
eBay

76 0000

eBay
1984
eBay, another similar by ponejail, eBay

Leitz

eBay

Lutz EX-3

Photoa, Photoc, eBay

1917 Ottway Ealing No 92

eBay

SAN (Chinese)

E-3 eBay looks like a copy of the C.T.I (above)

MA-5 MOM of Budapest Hungary

Similar to the Watts, but not an exact copy or even a completely different design.
Uses optical scales rather than a mechanical scale and vernier.



 

Watts

eBay

Wild

eBay Item 729809183 -

Plumbing Arm on Plane Table Case

eBay -

Brunton

Brass Reproduction

Fraud Aleart

eBay - tedamar

Repro at Yahoo Shops

Canyon Gold  -

Short Repro
 

Marine

Surveyors Plane Table -

Links

National Geodetic Survey - no instrument data

Antique Surveying Equipment - many instruments for sale:

Hilger & Watts 6200
 

1944 Gurley

Gurley 580

Dietzgen 6250

Mapping with a Plane Table and Alidade - instructions for use

Photos of field use -

NOAA Photo Library - drawing of an 1820 instrument - photo over water - 1894 instrument -

Stadia problem set as pdf document and another worked example -

Humboldt State University - Instrument Collection - Alidade-

Plane table - diagram of tripod to plane table connection, to accomadate leveling the table

Traditional alidade instruments combined with a Sokkia SET500 TS -

Plane table, alidade, and wye level - as a set.  Mentiones: A metal hinged plumbing arm to position the pointer and plum bob at any location on the plane table.

Instruments of Science and Technology - Plane Table Alidade. circa 1725 - Plane Table Alidade circa 1820 -

Photo of under side of 1840 table and French manuscript -

Finding the Way and Fixing the Boundary -

Manuals

U.S. Army TM 5-6675-211-15P - Dietzgen 6230 (10 to 18 power) & 6220 (12 to 24 power)

AG8 North Finding System

This is a gyroscope based instrument that finds true North.  Used by the military for artillery and for surveying in caves where much more accuracy is needed than can be had with a magnetic compass (or the compass does not work because of the location).

Some of the later PLGR GPS receivers and all of the DAGR GPS receivers have a "Gun Laying System" (aka North Finding) that is as accurate as the AG8, cost much less and can be held easily in one hand.  But will not work inside a tunnel, so there's still some need for the AG8.  The method depends on carrier phase tracking which is much more accurate than differential correction.

Kern DKM1
eBay not working
Note that it's possible to use two GPS fixes to determine North with high accuracy.  This can be done using two interconnected GPS receivers, like the PLGR or by using a single receiver like the DAGR.
The method may be similar to Differential Corrections, i.e. if the master GPS location is known (or determined by averaging) then range and range rate errors for each satellite can be determined and used to correct the slave GPS receiver.  Another method involves using carrier phase measurements and resolving the interger errors leading to cm accuracy.

Links

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