Maintenance of Levelling Equipment

Maintenance of  Levelling Equipment A) Levels (i) Store in a dry, secure place (ii) If the instrument gets wet, all surplus water should be removed with a dry cloth, using a clean tissue for the lens. Store the instrument in a warm secure place with the lid removed, to dry. (iii) Do not oil moving parts, clean them with a dry cloth. B) Tripods(i) Clean them at the end of each working day. (ii) Store them in a closed position carefully, and not thrown in the corner of a site hut. Remember that the purpose of a tripod is to provide a stable working base for the level. It will not do this if mishandled. (iii) Ensure that tripods feet do not become loose. (iv) The clamps on tripods legs tend to become less effective after long usage. Do not use nails, paper, etc., in order to tighten the legs, move the clamps further along the leg. (v) Bolts securing the tripod top to the legs work loose regularly – keep them tight. C) Levelling staves i) Clean each day after use and store correctly. ii) Wooden staves swell if wet. Take it apart and wipe off surplus water. Allow to dry naturally before reassembly.

Lesson Npte On Introduction to Drainage and Dewatering

Introduction to Drainage and Dewatering

What is drainage?

As the name itself suggests, drainage is the process in which the free water is removed with the help of gravity in order to maintain stable soil conditions.

Drainage can be classified into two categories:

1. Surface drainage
2. Sub-surface drainage

What is Surface drainage?

The water that runs on the surface of the ground is collected and or diverted into a water body.

Sub-surface drainage

It is the collection and disposal of ground water. It is also called as dewatering.

What is dewatering?

The process in which the water is removed from a foundation pit;

• when it is situated below the ground water table or
• when it is surrounded by a coffer dam.
• 

Why is dewatering done?

Only understanding the definition of dewatering is not enough. It is essential to know the reason as to why it is done.

Some times in some areas, the water table is high. This causes trouble and discomfort during construction. The water is pumped out so as to keep the excavation dry. Excavation has to be kept dry so that concreting can be done.

Sometimes temporary dewatering may suffice. Temporary dewatering is draining out the water at the time of construction and it is then followed by restoration to its original water level as soon as the construction is complete.

What is permanent dewatering and why it is done?

Permanent dewatering is removing the subsurface gravitational water throughout the life of the structure. This is done to protect the structure from moisture and dampness.

Advantages of Subsurface drainage

It helps in improving the properties of the soil

Helps in the stabilization of soils

Let us consider the case of “Fine grained soil”

The water removed from fine grained soil is not much but the improvement in the properties of the soil is significant.

Helps in reducing hydrostatic pressure acting at the base of the structure

Methodology to be adopted for Sub-surface drainage:

The methodology adopted at a site would depend on various factors. They are as follows:

• Characteristics of the soil
• Position of the water table
• Time period.

Lesson Note On Definitions of GIS

Definitions of GIS

Geographic Information System (GIS) has been defined in various ways by different authorities. A typical GIS can be understood by looking at its various definitions. In this section, we present different definitions (or descriptions) of GIS that have been offered by people.
Burrough (1986) defines GIS as a "set of tools for collecting, storing, retrieving at will, transforming and displaying spatial data from the real world for a particular set of purposes".

In his own definition, Arnoff (1989) defines GIS as "a computer based system that provides four sets of capabilities to handle geo-referenced data: data input, data management (data storage and retrieval), manipulation and analysis, and data output."
“A geographic information system (GIS) is a computer-based tool for mapping and analysing things that exist and events that happen on earth. GIS technology integrates common database operations such as query and statistical analysis with the unique visualisation and geographic analysis benefits offered by maps” (ESRI, 1990).

". . . The purpose of a traditional GIS is first and foremost spatial analysis. Therefore, capabilities may have limited data capture and cartographic output. Capabilities of analyses typically support decision making for specific projects and/or limited geographic areas. The map data-base characteristics (accuracy, continuity, completeness, etc.) are typically appropriate for small-scale map output. Vector and raster data interfaces may be available. However, topology is usually the sole underlying data structure for spatial analyses" (Huxhold, 1991 p.27).

"A geographic information system is a facility for preparing, presenting, and interpreting facts that pertain to the surface of the earth. This is a broad definition . . . a considerably narrower definition, however, is more often employed. In common parlance, a geographic information system or GIS is a configuration of computer hardware and software specifically designed for the acquisition, maintenance, and use of cartographic data" (Tomlin, 1990 p xi).

"A geographic information system (GIS) is an information system that is designed to work with data referenced by spatial or geographic coordinates. In other words, a GIS is both a database system with specific capabilities for spatially-reference data, as well as a set of operations for working with data . . . In a sense, a GIS may be thought of as a higher-order map" (Star and Estes, 1990, pp. 2-3).
A GIS is "an organised collection of computer hardware, software, geographic data, and personnel designed to efficiently capture, store, update, manipulate, analyse, and display all forms of geographically referenced information" (ESRI, 1990, pp. 1-2).

“A Geographic Information System (GIS) is a collection of computer hardware, software and geographic data used to analyse and display geographically referenced information” (URL1).
“A GIS is a computer system capable of capturing, storing, analysing, and displaying geographically referenced information; that is, data identified according to location. (Some GIS) practitioners also define a GIS as including the procedures, operating personnel, and spatial data that go into the system” (URL2).

“In the strictest sense, a GIS is a computer system capable of assembling, storing, manipulating, and displaying geographically referenced information, i.e. data identified according to their locations. GIS practitioners also regard the total GIS as including operating personnel and the data that go into the system” (URL2).
“GIS is an integrated system of computer hardware, software, and trained personnel linking topographic, demographic, utility, facility, image and other resource data that is geographically referenced” (URL3).

A list of additional definitions of GIS can be found in Longley et al (2001). By way of summary, GIS can be considered to be a computer-based system comprising hardware, software, geographically-referenced data, personnel and procedures put together for the input, storage, retrieval, analysis, manipulation, query, update and output of geographical data.

V60 RTK

https://youtu.be/H500ThKquYs

Survey Professionals in Nigeria- SURCON

In the Council there are four Registers, one for each category of survey practitioners registered.

The Surveyors Council of Nigeria (SURCON) was established following the promulgation on 14th December 1989, of Decree 44 known as the Surveyors Registration Council of Nigeria Decree otherwise known as the Surveyors Council of Nigeria (SURCON). After codification, the Enabling Decree is now known as CAP 425 Laws of the Federation of Nigeria 1990.

Surveyors

There is a total of 2088 Surveyors in Nigeria. This number is made up of Principals and Non-Principals. Non-Principals are all Surveyors in paid employment and for the year 2012, 306 of these are up to date. The principal surveyors are the executive and chief executive in private and public companies and organizations. 1085 of them are enlisted to practice while 844 are not up to date for the year 2012.

Pupil Surveyors

These are graduates from Universities and post HND polytechnic graduates that have registered with the Council. As at February 2012, there are 1212 in this category. They would be eligible to do the professional exams after 2 years pupilage.

Technologists

These are Polytechnic HND graduates that have registered with the Council. As at February 2012, there are 356 in this category.

Technicians

These are polytechnic ND graduates who have registered with the Council. As at February 2012, there are 104 of them.

Map Projections

Even though they are easy to fold up and carry around,
neither greatly distorted maps nor disassembled globe
gores have much practical use. For this reason,
cartographers have developed a number of map projections,
or methods for translating a sphere into a flat surface. No
projection is perfect - they all stretch, tear or compress the
features of the Earth to some degree. However, different
projections distort different qualities of the map. "All maps
have some degree of inaccuracy," Turner explains. "We're
taking a round Earth and projecting it onto a two-
dimensional surface -- onto a piece of paper or a computer
screen -- so there's going to be some distortion."
Fortunately, the variety of available projections makes it
possible for a cartographer to choose one that preserves
the accuracy of certain features while distorting less
important ones.
Creating a map projection is often a highly mathematical
process in which a computer uses algorithms to translate
points on a sphere to points on a plane. But you can think
of it as copying the features of a globe onto a curved
shape that you can cut open and lay flat -- a cylinder or a
cone. These shapes are tangent to, or touching, the Earth
at one point or along one line, or they are secant to the
Earth, cutting through it along one or more lines. You can
also project portions of the Earth directly onto a tangent or
secant plane.

Projections tend to be the most accurate along the point or
line at which they touch the planet. Each shape can touch
or cut through the Earth at any point and from any angle,
dramatically changing the area that is most accurate and
the shape of the finished map.
A planar projection
IMAGE COURTESY NATIONAL ATLAS
Some projections also use tears, or interruptions, to
minimize specific distortions. Unlike with a globe's gores,
these interruptions are strategically placed to group related
parts of the map together. For example, a Goode
homolosine projection uses four distinct interruptions that
cut through the oceans but leave major land masses
untouched.
A Goode projection of the Earth
IMAGE USED UNDER THE GNU FREE DOCUMENTATION
LICENSE
Different projections have different strengths and
weaknesses. In general, each projection can preserve
some, but not all, of the original qualities of the map,
including:
Area: Maps that show land masses or bodies
of water with the correct area relative to one
another are equal-area maps. Preserving the
correct area can significantly distort the shapes
of the land masses, especially for views of the
entire world.
Shapes: In the pseudoconical Robinson
projection, the continents are shaped correctly
and appear to be the correct size -- they look
"right." However, distances and directions are
incorrect on a Robinson projection. It's a good
tool for studying what the world looks like but
not for navigating or measuring distances.
Distances: Maps that maintain correct
distances between specific points or along
specific lines are equidistant maps.
Directions: Many navigational maps have
straight rhumb lines, or lines that intersect all of
the parallels or meridians from the same angle.
This means that, at any point on the map,
compass bearings are correct.
You can learn more about the specific map projections and
their strengths and weaknesses from NASA , the National
Atlas of the United States and the U.S. Geological Survey .
Choosing the right projection is just one part of creating a
successful map. Another is finding the right data. We'll
look at where map information comes from in the next
section.