Lec 8: Basic Navigation Concepts

Nighttime Aerial Photography (cf. Assignment 2)

Does it exist?

Announcements

Question re Readings included in Final Exam...

Ombudsmeeting

The Readings for Today’s Lecture were:

Ch. 14: Compass and Maps

Comments or Questions?

(General, Lab, Assignment, Readings)

Today’s Lecture:

Distance

Raster GIS Operations Clinic

Basic Navigation Concepts (“Part I”)

The Basic Navigation Concepts unit is

based on Chapter 14 “Compass and Maps”

(Appendix D Navigation Instruments will be covered a bit later)

Distance (“debt”)

Raster GIS Operations Clinic

Non-linear Spread (recap)?

Discussion of:

Clump

Count

(SubScene)

Basic Navigation Concepts

The “Uh, where are we?” problem (cartoon)

The structure of Chapter 14

Orienting the Map

What does this mean?...

Inspection method

based on co-visible (or co-sensed) features

Celestial features

using sun and stars — especially the North Star

Terrestrial features

One linear feature

Two linear features

Prominent objects

Fig. 14.1

Problem with potential reversal of orientation (by 180 degrees)

Compass method

Two necessary conditions:

must have a compass

must know the local magnetic declination

ie. the direction of magnetic north

Fig. 14.2

Establishing Your Position

Three methods

by inspection

by instruments

by local reference

Inspection method

two main inspection techniques:

distance estimation

resection

Distance estimation

select a co-visible feature

estimate ground range

convert to map distance (using the map scale)

mark on map along the proper distance line

you can double check by using more than one feature

range finders

stadia and graduated rod

prismatic rangefinder

laser rangefinder (aka Electronic Rulers or EDMs - Electronic Distance Measurers)

Fig. 14.3

Resection method

this is a less casual and more robust method

based on plotting two or three crossing lines

Done by identifying co-visible features

and “raying them in”

these sight lines are drawn using a ruler

and really represent a backsight or back bearing

ideally at least 2 of the lines should cross at about 90 degrees

note that 3 lines will produce a useful triangle of error

with only two lines thre’s the possibility of a hidden error

Fig 14.4

Break

Instrumental methods

Celestial observation

sextant

Q: what doe this thing do and how?...

Fig. 14.5

Electronic positioning

Self-contained systems

require no external information source

a kind of modern-day automated dead-reckoning system

forms the basis for modern inertial navigation system (INS)

Signal-dependent systems

ground-based radionavigation aids

include passive and active systems

passive reception from one or more radiobeacons (Rbns)

the receiving unit is called a radio direction finder (RDF), or radio compass

Fig. 14.6

active systems

radar (radio detection and ranging)

sonar (sound navigation ranging)

modern systems

GPS (Global Positioning System) to which the whole next chapter in the text (No. 15) is devoted

GLONASS (GLObal NAvigation Satellite System)

Compass method

advantages of compass over inspection method:

a compass can provide a more accurate direction

no need to orient the map to the north

as with the inspection method, there are two ways to work with a compass to establish position:

Distance estimation

Resection

Distance estimation

use the compass to get a bearing to a feature

estimate the distance (using the previously described methods)

convert to map distance (using the map’s scale)

plot it on the map

Fig. 14.7

Resection

same as resection method under the inspection technique, but this time with the aid of a compass,

no need for a sight-rule (alidade) or a straight-edge (for ‘aiming’ and plotting)

use a protractor to plot the bearing

Fig. 14.8

use two or three points (as before)

if you only have two points, or if you have three but want high accuracy),

then repeat the measurements (eg. twice)

and get a ‘point-cluster error’ instead of an error triangle

*********************

Altimeter method

These guys (altimeters) become particularly useful in mountain environments

where the position is defined by [X,Y,Z], it helps having Z info in order to figure out the position [X,Y]

Equiped with topo map (has contour lines) and pocket altimeter, only one ground feature is sufficient to get a position fix

linear features are particulary useful (know as ‘handrails’ in the science/art/sport of orienteering)

Barometric altimeters need to be calibrated

Q: how and when is this done?

Q: What other kind of altimeters are there?

Linear feature altimeter procedure

Fig. 14.9

Sight line altimeter procedure

first establish sight line to a distant object and plot it

read altimeter elevation

follow sight line until it ‘hits’ the correct elevation

Fig. 14.9 also shows this method

Local reference method

when there are no aids (including) map

and high precision isn’t required

the fisher’s solution

locate two pairs of features on opposite sides of the lake

wide angle, eg. 45 degrees

or better still, line up two pairs of features along one shoreline

in effect this amounts to crossed backsights (and thus is a type of resection)

Fig. 14.10

‘til next week!