UNIVERSITY OF SOUTH ALABAMA
GY 301: Geomorphology
Lecture 5:
Alidade & Plane
Table Methods
Last Time
Another Simple day;
Topographic profiles
Drawing topographic profiles
Vertical exaggeration
Topographic Profiles
Topographic Profiles
Vertical Exaggeration
Today’s Agenda
Most profiles and cross sections have different vertical and
horizontal scales
This is intentional; it focuses attention on vertical relief….
…. However, you must calculate and report this vertical
exaggeration on all profiles/cross sections
The Alidade and Plane Table Surveying
Alidade procedures
Reading elevations
Surveying tricks
Vertical Exaggeration = Horizontal distance/Unit
Vertical distance/Unit
1
Alidade & Plane Table
Alidade & Plane Table
• Used to make large scale maps (i.e. maps that
show great detail over very small area, 1 inch
= 10 feet is typical)
Alidade & Plane Table
• Used to make large scale maps (i.e. maps that
show great detail over very small area, 1 inch
= 10 feet is typical)
• Used to construct topographic maps where
none exist
Alidade & Plane Table
Alidade & Plane Table
• Used to make large scale maps (i.e. maps that
show great detail over very small area, 1 inch
= 10 feet is typical)
• Used to construct topographic maps where
none exist
• Are ideal for contouring complex topography
because the plane table allows for drawing the
contours on-site
Alidade & Plane Table
http://www.harborfreight.com/cpi/photos/96600-96699/96669.gif
Basic Plane table surveying
An early model alidade
http://www.hugha.co.uk/Tanzania/TanReporter52_files/LR006.jpg
http://www.hugha.co.uk/Tanzania/TanReporter52_files/LR006.jpg
2
Parts of an Alidade
1: Telescope
3: Blade
4: Pedestal
6: Axis clamp screw
7: Tangent screw
8: Striding level
10: Fiducial edge
11: Bulls eye level
12: Azimuth adjustment
13: Compass box
14: Compass needle
lever
15: Eyepiece
16: Stadia hairs
17: Eyepiece focus
19: Sun shade
20: lens cover
21: retaining ring
• Stadia Rod: usually a 10 foot rod with feet
and 0.1 foot divisions painted on the rod
22: vertical angle level
25: Vernier scale
23: vertical angle frame
26: Vernier calibration mark
24: vertical angle adjustment
Measurements with the Alidade and
Stadia Rod
•
Setup of the instrument includes:
1.
2.
3.
4.
5.
Measurements with the Alidade and
Stadia Rod
Leveling the plane table
Drawing magnetic north reference line
Measuring the instrument height
Recording of scale (ensure all features to be mapped will fit on map)
Recording of ground elevation directly below the center of the plane table
Geometry of Alidade Measurements
• Stadia intercept: distance on rod from lower to upper
horizontal stadia line; distance ratio is 1:100
ALIDADE STADIA CROSS HAIR
vertical cross hair
full stadia
intercept
10
half stadia
intercept
horizontal cross hair
9
8
quarter stadia
intercept
quarter interval
cross hair
stadia rod
stadia intercept = 9.9 - 7.5 = 2.4 feet
distance = 2.4 x 100 = 240 feet
http://nationalatlas.gov/articles/government/IMAGES/usgs_topographer.gif
http://www.pssac.org/SoilMappingHistory/Plane%20Table%20and%20Alidade.gif
Geometry of Alidade Measurements
• Vertical angle measurement with Vernier scale
clinometer
E
Ray Measurement Geometry
• Measurements from the alidade station to a data point are
termed rays
E
E
3
Ray Measurement Geometry
Ray Measurement Geometry
• Measurements from the alidade station to a data point are
termed rays
• The ray is drawn on the plane table to track distance and
direction, and the elevation of the ray endpoint is calculated in
field notes
• Measurements from the alidade station to a data point are
termed rays
• The ray is drawn on the plane table to track distance and
direction, and the elevation of the ray endpoint is calculated in
field notes
• A correction must be made for the difference between the
alidade cross hair (CH) intercept and the instrument height
(IH) of the alidade
Ray Measurement Geometry
Ray Measurement Geometry
•
•
•
Measurements from the alidade station to a data point are termed rays
The ray is drawn on the plane table to track distance and direction, and the
elevation of the ray endpoint is calculated in field notes
A correction must be made for the difference between the alidade cross hair (CH)
intercept and the instrument height (IH) of the alidade (see below):
Plane Table + Alidade
Stadia rod
•
•
•
Measurements from the alidade station to a data point are termed rays
The ray is drawn on the plane table to track distance and direction, and the
elevation of the ray endpoint is calculated in field notes
A correction must be made for the difference between the alidade cross hair (CH)
intercept and the instrument height (IH) of the alidade (see below):
IH=3.5ft
Elevation=161ft
Ray Measurement Geometry
•
•
•
Measurements from the alidade station to a data point are termed rays
The ray is drawn on the plane table to track distance and direction, and the
elevation of the ray endpoint is calculated in field notes
A correction must be made for the difference between the alidade cross hair (CH)
intercept and the instrument height (IH) of the alidade (see below):
IH=3.5ft
•
•
•
Measurements from the alidade station to a data point are termed rays
The ray is drawn on the plane table to track distance and direction, and the
elevation of the ray endpoint is calculated in field notes
A correction must be made for the difference between the alidade cross hair (CH)
intercept and the instrument height (IH) of the alidade (see below):
IH=3.5ft
Cross hair (CH)
= 5.7ft
Elevation=161ft
Ray Measurement Geometry
5.7ft
Cross hair (CH)
= 5.7ft
5.7ft
Elevation=161ft
Elevation @ Rod = 161ft + (IH-CH)
= 161ft + (3.5ft-5.7ft)
= 161ft – 2.2ft
= 158.8ft
4
Ray Measurement Geometry
Ray Measurement Geometry
• When slope angles and distances become large the alidade
telescope must be inclined to view the stadia rod
• When slope angles and distances become large the alidade
telescope must be inclined to view the stadia rod
• A trigonometric formula must be used to take the inclination
of the telescope into account
Ray Measurement Geometry
Worksheet for Alidade Data
•
When slope angles and distances become large the alidade telescope must be
inclined to view the stadia rod
• A trigonometric formula must be used to take the inclination of the telescope into
account (see below):
Upper stadia
Stadia rod
Net horz. offset = SD * (cos (VA-30))2
Lower stadia
You must make the following measurements for each ray:
1.
Stadia intercept: difference between upper and lower stadia hairs on the
stadia rod
2.
Cross hair intercept: where the central horizontal cross hair intersects the
stadia rod
3.
Vertical angle: vertical angle read from clinometer (including the Vernier
scale)
Net vert. offset = SD * (tan (VA-30))
Elevation change
Worksheet for Alidade Data
Plane table site location description:
Party and date:
Vert. angle
(VA)
Plane table site elevation (SE):
161.10
Instrument height (IH):
3.50
Stadia intercept
Horizontal map distance
Alidade Mapping Strategy
Rod point
R-1
R-2
R-3
SI
1.20
3.50
8.13
Stadia distance
Cross hair
Vertical angle
Net horz. dist.
SD (1:100)
CH
VA
SD*(Cos(VA-30))^2
120.00
350.00
813.00
6.50
5.50
3.30
33.50
34.50
27.80
Net elev. change (EC)
Rod elev.
SD*(Tan(VA-30))+(IH-CH)
119.55
347.85
811.80
SE+EC
4.34
25.55
-31.03
NOTES
165.44 ray from 1st alidade station to tree #1
186.65 ray from 1st alidade station to tree #2
130.07 ray from 1st alidade station to elevation control point
Alidade Mapping Strategy
• You should not try to shoot a ray > 250ft
with the alidade unless you have no choice
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Alidade Mapping Strategy
Alidade Mapping Strategy
• You should not try to shoot a ray > 250ft
with the alidade unless you have no choice
• Moving the alidade from one station to
another station is “traversing” the instrument
• You should not try to shoot a ray > 250ft
with the alidade unless you have no choice
• Moving the alidade from one station to
another station is “traversing” the instrument
• You should shoot rays to all needed control
points around the 1st station, then shoot the
last ray to the new 2nd station position
ST1
ST2
Alidade Mapping Strategy
• You should not try to shoot a ray > 250ft
with the alidade unless you have no choice
• Moving the alidade from one station to
another station is “traversing” the instrument
• You should shoot rays to all needed control
points around the 1st station, then shoot the
last ray to the new 2nd station position
Alidade Mapping Strategy
• You should not try to shoot a ray > 250ft
with the alidade unless you have no choice
• Moving the alidade from one station to
another station is “traversing” the instrument
• You should shoot rays to all needed control
points around the 1st station, then shoot the
last ray to the new 2nd station position
R1
ST1
R2
R1
ST2
ST2
Alidade Mapping Strategy
• You should not try to shoot a ray > 250ft
with the alidade unless you have no choice
• Moving the alidade from one station to
another station is “traversing” the instrument
• You should shoot rays to all needed control
points around the 1st station, then shoot the
last ray to the new 2nd station position
Alidade Mapping Strategy
R2
R1
ST1
ST1
R3
• You should not try to shoot a ray > 250ft
with the alidade unless you have no choice
• Moving the alidade from one station to
another station is “traversing” the instrument
• You should shoot rays to all needed control
points around the 1st station, then shoot the
last ray to the new 2nd station position
R2
R1
R3
ST1
R4
ST2
ST2
6
Alidade Mapping Strategy
• You should not try to shoot a ray > 250ft
with the alidade unless you have no choice
• Moving the alidade from one station to
another station is “traversing” the instrument
• You should shoot rays to all needed control
points around the 1st station, then shoot the
last ray to the new 2nd station position
Alidade Mapping Strategy
R2
R1
R3
ST1
• You should not try to shoot a ray > 250ft
with the alidade unless you have no choice
• Moving the alidade from one station to
another station is “traversing” the instrument
• You should shoot rays to all needed control
points around the 1st station, then shoot the
last ray to the new 2nd station position
• You will need to calculate the elevation at
the new 2nd site, and start a new data sheet
with a new instrument height recording
R2
R1
R3
ST1
R4
R4
ST2
R7
ST2
R5
R6
Alidade Mapping Strategy
• You should not try to shoot a ray > 250ft
with the alidade unless you have no choice
• Moving the alidade from one station to
another station is “traversing” the instrument
• You should shoot rays to all needed control
points around the 1st station, then shoot the
last ray to the new 2nd station position
• You will need to calculate the elevation at
the new 2nd site, and start a new data sheet
with a new instrument height recording
• Since you are to produce a topographic map
you may need supplemental elevation
control points in addition to the feature that
you are mapping (geological contact,
building plan, etc.)
Baseline Triangulation
• By establishing a measured baseline objects can be
accurately surveyed in terms of map position without
stadia rods
R2
R1
R3
ST1
Target2
Target1
R4
R7
ST2
R5
Station1
Measured baseline
Station2
R6
Baseline Triangulation
Baseline Triangulation
• By establishing a measured baseline objects can be
accurately surveyed in terms of map position without
stadia rods
• By establishing a measured baseline objects can be
accurately surveyed in terms of map position without
stadia rods
Target2
Target2
Target1
Station1
Target1
Measured baseline
Station2
Station1
Measured baseline
Station2
7
Baseline Triangulation
Baseline Triangulation
• By establishing a measured baseline objects can be
accurately surveyed in terms of map position without
stadia rods
• By establishing a measured baseline objects can be
accurately surveyed in terms of map position without
stadia rods
Target2
Target2
Target1
Station1
Target1
Measured baseline
Station2
Station1
Measured baseline
Station2
Upcoming Stuff
Homework
Finish lab 2 (due Friday)
Next Lecture:
Geomorphology and Surface Processes 1: The
coastline
Friday’s Lab:
Inside: Coastline geomorphology map interpretations
(Independent Assignment)
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