Why GPS is used as Survey tools?

About GPS

Global Positioning System (GPS) technology is a space-based radio-navigation system that provides users worldwide with valuable information including three-dimensional position, navigation, and velocity and time data. It comprises of 24 satellites, which are in orbit some 12,000 miles above the earth’s surface. GPS operates on the principle of triangulation. The satellites broadcast their position on a continuous basis, and by combining the measurements from different satellites.

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Another user-friendly aspect of GPS is the fact that it is not affected by weather conditions. This technology is easily integrated with geographic information systems and is, therefore, very useful for engineering and surveying applications. GPS technology provides highly accurate information, including digital maps of land and infrastructure, such as highways.

How GPS Can Assist in Surveying

Conventional surveying can be extremely costly and time-consuming. Surveyors often need to make multiple visits to the same site in order to gather data and ensure that it is accurate. They must also be trained in the operation of complex technical equipment. Weather conditions such as snow, rain and extreme temperatures can also delay the collection and checking of data. The surveying industry is increasingly coming to recognize the need to reduce labor costs, while increasing the accuracy of surveys. An effective way of doing this is to use GPS technology.

For Example

In a current GPS surveying project, which found that one surveyor operating GPS surveying equipment is twice as fast as a conventional surveying crew, and a GPS system with two units has the potential to be four times faster than crews using conventional technologies to complete surveys. Another advantage of the GPS surveying technology is the fact that it can be used over long distances with far fewer setups. It can be setup and surveys can be performed over a distance of six miles from the base unit, whereas with conventional equipment the base unit would have to be moved every 600 feet.

Key Advantages

  • GPS surveying can save significantly on labor costs
  • GPS surveying is highly accurate
  • GPS is time saving for civil engineers

training course in GPS Surveying is available at KIG. for more information click here.

Site Positioning – GPS or Total Station?

Today’s Site Positioning Systems tools that allow a variety of grade checking, positioning and measuring jobs to be performed faster throughout the life cycle of the project. The world has never seen the perfect tool that does it all. In the positioning domain, both GNSS and total stations have earned their place. Especially in the construction and machine control industries, these systems have become commonplace. GNSS has strengths over total stations and total stations have strengths over GNSS. Site Positioning Systems today, have evolved from being high precision complex surveying tools, to being much simpler and easier to use.

However, one question I hear a lot is “should I use GPS or Total Stations?” There is no one right answer for this, since it really depends on a number of factors. Depending upon the type of work being performed, there is some combination of price and performance within these scales to best fit a job. But deciding upon the best solution is not always easy or obvious. But, there are some good general guidelines you can follow:

1GPS receiver based systems are ideal for larger jobsites, and accuracy requirements of 8 millimeters. Since they depend on satellite signals they work best on sites with a reasonably unobstructed view of the sky. They can be used on a pole or mounted on a vehicle. As a pole mounted system GPS systems are ideal for moving about on the job site collecting a lot of data—grade checking, measuring volumes, doing asbuilts and more. As a vehicle mounted system, GPS systems provide supervisors with a view of the job site and the job progress comparable to what the operator using machine control sees. Today’s GPS receivers typically track all the major satellite constellations GPS, GLONASS, Galileo and Compass and are referred to as “GNSS receivers”. Because they are tracking more satellite constellations, GNSS receivers can provide better coverage and performance even in tough environments near buildings, under tree canopy or in deep cuttings or mines.

Total Station based systems provide the highest possible degree of accuracy for site positioning, stakeout, grade checking and measurement. A Total Station-based system has a more limited range than a GNSS-based system and is better suited for projects where accuracy is a key factor. They are ideal for sites where the accuracy requirements are very tight: 3 millimeter. There are also Total Station systems that use “reflectorless measurement” technology.  Reflectorless technology provides you with the ability to accurately measure a position at a distance without the need for a prism, making these systems ideal for taking volume and progress measurements in dangerous or inaccessible locations.

With all these variables, how does the potential buyer go about determining the best fit for their particular needs? There is no easy answer. This article has looked at some considerations that should be taken into account. Besides these, many other factors can be considered: Portability, ruggedness, power autonomy, system complexity or ease of use, local support, the ability of the instrument to perform secondary tasks, reliability, governmental regulations, etc.

Whether you need the convenience and flexibility of a GNSS-based system, or the tight accuracy of a Total Station-based system, it is equally as important to evaluate the field and office software. Make sure the software has been developed specifically and that it has the flexibility and expandability to handle all the site positioning and measurement tasks you need on your projects. Unless money is no object, there will likely be some type of compromise. Ideally, an end user has access to both the high-end GNSS and total station solutions.

Training on Total Station and GPS is viable at Khagolam Institute of Geoinformatics

Total Station – Essential Skill for Civil Engineering Students

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Total Station is the most widely preferred modern surveying instrument in the civil engineering industry. Civil engineers, knowledge with the use of Total Station are hence preferred in the industry. However, Total Station is absent in the current schemes of engineering education and in some engineering education institute it’s just introduced as theoretically. To become experts, hence propose getting industrially trained in using Total Station surveying equipment. It would positively enhance employability of civil engineering students in India.

Surveying is widely used across various engineering domains, specifically essential for civil engineering projects. It helps in designing a three-dimensional terrestrial plan or map of a particular area. The angles and distances of relevant topographic points are measured with the help of surveying equipment.

Various categories of Surveying are Geodetic Surveying, Cadastral Surveying, and Topographical Surveying, Hydrography surveying and Aerial Surveying using Photogrammetry, LiDAR.

Fundamental techniques used for Surveying are Triangulation, Trilateration, Traverse, Leveling and Radiation.

Total station is basically a theodolite or an instrument to measure angles across horizontal and vertical planes. It is additionally equipped with an EDM to evaluate relative terrestrial distances (slope distance). A Total Station is a real-time system embedded with an on board computer to get live computational coordinate and elevation. Using real-time measurements, the on board computer is capable of resolving or adjusting data and setting construction points. Some Total Stations are also robotic which enables the surveyor to utilize the device remotely with the help of a controller.

Total Stations use computational methods for processing and analysis of surveyed data. Some total stations are also equipped with Global Navigation Satellite System to enable coordinate measurement of surveyed points.

Total Stations are also integrated with Global Positioning System (GPS) technology and Geographic Information System (GIS) which facilitates accurate mapping of survey points. Data collected from Total Stations are also used for Building Information Modeling (BIM), i.e. the representation of construction characteristics graphically. Computer Aided Design (CAD) is extensively used for this purpose. Map data collected from Total Stations can also be projected on Google Earth.

Apart from surveying in civil engineering, Total Stations find applications in archaeology, surveying work required for mining, Hydrography and in many more possible domains. The working knowledge of Total Stations hence would be an added advantage to the skill sets of civil engineering students.

Total Station is training is available at Khagolam Institute of Geoinformatics

What is Contour Survey?

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In olden times, map makers were the revered artisans and scientists of their day. They were the creators of outlines of continents and the illustrators of sections of unexplored oceans. Land surveyors blow past this antiquated mapping model, stacking dimensional aspects on top of information-constricting two dimensional assets thanks to developments in contour mapping.

A contour survey maps crucial elevation data onto parcels of land, outlining a real-world topographical view. The height datum partners with area outlines to show detailed spatial information, translating that data into contours that can be rendered within a flattened perspective. Any engineer, architect, or construction expert can then easily decipher the contours, how they band, the distance between the bands, and other relevant factors. For example, the rise and fall of soil within the parcel of land, the irregularities that define its topography, will assist a civil engineer in planning drainage ditches and flood remediation strategies. Additionally, the contours illustrate how the land falls off around an existing property, thus demonstrating obstructions to a planned home extension.

On Carrying Out the Process

It’s not a particularly challenging task, but readers need to be aware that a single error in a contour survey will affect every stage of the construction process. Floor levels and retaining walls will be ever so slightly off because of poor data collection, and this mistake will have effect continuous, spreading outward to throw off other measurements. It’s therefore essential to hire a reputable land surveyor, someone who can set a solid bench point and gather height datum from a grid of data points as set along the property parcel. Specialist spatial measuring tools are used to accurately aggregate the dimensional information, with new techniques being developed that create a “cloud” of data points. Imagine lasers and radio scanning tools that can make a high-resolution map of all three dimensions within minutes.

Compiling Contour Survey Data

It typically depends on the level of expertise of the survey professional, but the gathered data is going to be useless, unless it’s translated into the standard contour map format. One answer to this question is to use specialist computer software, a digital terrain model (DTM). Here’s a few rules and directives that govern the deciphering of a contour survey.

  • The closer the bands are, the greater the gradient of the land. The reverse also holds true
  • Contours do not cross
  • When the spacing in equal, this indicates a uniform section of land

There are, of course, many other cues to become familiar with, and only a surveyor can properly provide these contoured survey outlines. Ensure your contour survey is professionally commissioned if you want to build on a complex section of topography. This way, you’ll always be able to calculate the volume of soil to remove or add, and know the precise depth of services.

WHAT IS SURVEYING & SURVEYOR?

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DEFINITION OF SURVEYING

The art, science, and technology of determine the relative position of points at, above, or below the surface of the earth or establishing such points.

DEFINITION (according to its true nature and scope)

The art, science, and technology of gathering and analysing measurement data related to the land and other land-related surfaces and spaces, to include designing and determine the measurement specifications and standards to accomplish these measurements with the desired precision and accuracy. The error control and adjustment, including the use of all instrumentation applicable to such measurements, said measurements typically being, but not limited to distances, heights, angles, directions, positions, areas, volumes, and other measurements associated with these quantities.

PROFESSIONAL SURVEYING 

  • Field surveying for Topographic and other Maps
  • Geodetic and other Precise Control Surveys
  • Layout and Staking to Guide Construction
  • Retracement of Property Boundaries
  • Photograrnmetry Surveys for Topographic and other Maps
  • Making Surveys and Maps for Land Information Systems
  • Measuring and Plotting the Position of Constructed Works
  • Surveys for Mining and other Subsurface Operations
  • Hydrographic and Underwater Surveys
  • Construction of Maps and other Graphics for Design and Planning 

THE VALUE OF BEING A SURVEYOR:

The surveyor is primarily an analyst. As an analyst of both measurement data and boundary location evidence (including geometric and other mathematical relationships) the surveyor is in a position to develop a keen sensitivity to the importance of finding and applying the truth. A surveyor, when practicing according to the true nature of surveying, is ever seeking the truth, whether in measurement or in boundary location. Consequently, learning and applying the measurement science and the legal and other principles of boundary retracement develops character.

The art and science of surveying is a mirror of life itself called “Geomatics” in Canada and much of Europe, land surveying is known as the world’s second-oldest profession. It dates back to ancient Egypt and Babylonia. Surveying is essentially the art and science of measuring and mapping land. While the entire scope of our profession is vast, it all eventually boils down to determining where people land boundaries are located. Without this service, railroads could not be built, skyscrapers could not be erected, and individuals could not put up fences around their yards, for fear of trespassing on someone else’s land. Would you like an interstate highway to be built in your backyard, one you’ve paid for, maintained, and paid taxes on for years, without your permission? Of course, how would you know it was in your backyard without a surveyor to tell you where your property even was? We also stake out boundaries of roads to be built, monitor skyscrapers to make sure they are being erected vertically, and measure airports so that the runways are perfectly aligned and smooth. So, if you see a guy in the road looking through an instrument on a tripod that is a surveyor, now you know that he is doing more than taking pictures.

What is a surveyor?
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A surveyor is more than one of those guys you see out in the road. Surveying is a vital part of the design and construction process. We perform boundary surveys to tell people where their property is, map the topography of land for engineering design, establish elevations of home sites for flood insurance, perform title surveys for real estate transactions, certify that structures are built according to design, layout buildings, subdivisions and other construction projects so the construction companies can relate the engineering plans to the real world, and build control networks that all land parcels can relate to in a given area. We also map slopes and areas for pay volumes or quantities, map river bottoms for dredging, lay out photo control for aerial photography and photogrammetry, write legal descriptions that are used to describe pieces of property, map and layout corridors for tunnels, roads, airports, pipelines, cellular networks and railroads, and split up properties into new lots, such as subdivisions.

Total Station and GPS surveying training is available.

 

Adding number of vertices in the attribute table:

QGIS does not have the Vertices Counter tool to process, therefore you have to download the plugins called Vertices Counter.

Follow the procedure:

  • Go to the Plugins → Manage and Install Plugins
  • Type Vertices Counter on the search box and then install plugin.

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Plugin

  • Then add your vector data to count vertices.
  • Then Go to Vector  Vertices Counter Vertices Counter

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By default it will take the active layer as an input, you can select the desired layer from the select layer. It will activate when you check box the select from the loaded layers. Under option check the box of Create New Column if you want to add vertices value in the attribute table, if not check Count without adding column. Results will display on the window or you can export the results in CSV format.

Vertices window

  • Now open the attribute table of Active layer by right clicking the layer → Open Attribute Table. You will notice vertices values are added in an attribute table.

Final

for details QGIS Training visit Khagolam.com

Searching and Downloading OpenStreetMap Data

Getting high quality data is essential for any GIS task. One great resource for free and openly licensed data is OpenStreetMap (OSM). The OSM database consits of streets, local data as well as building polygons. Getting access to OSM data in a GIS format is integrated in QGIS. This tutorial explains the process for searching, downloading and using OSM data in QGIS.

Search for OSM database, browse and select a part of the Area of intereset, and extract data as a shapefile.

Procedure

Make sure you have installed OpenLayers plugins.

The OpenLayers plugin is installed under the Web menu. This plugin allows you to access basemaps from various providers in QGIS.

  • Let’s load the OpenStreetMap basemap in QGIS by going to Web Menu ‣ OpenLayers plugin ‣ OpenStreetMap ‣ OpenStreetMap layer.

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You will see a world map loaded in QGIS.

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  • Now, let’s search for your Interested area, I will search kalian West area.

You will see the base layer move and center around the Area of Interested. You can use the Zoom tool to zoom and select the exact area of your interest. For this tutorial, you can zoom in the center of the city as shown.

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  • Now we can download the data displayed on the map canvas. Go to Vector ‣ OpenStreetMap ‣ Downlod data.

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  • In the Download OpenStreetMap data dialog, choose From map canvas as the Extent. Choose the path and name the output file as Kalyan.osm and Click OK.

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  • The downloaded file with the .osm extension is an text file in the OSM XML format. We first need to convert it into a suitable format that is easy to consume in QGIS. Go to Vector ‣ OpenStreetMap ‣ Import topology from XML.

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  • Choose the downloaded Kalyan.osm as the Input XML file. Name the Output SpatiaLite DB file as Kalyan.osm.db. Make sure the Create connection (SpatiaLite) after import button is checked. Click OK.

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  • We need to create SpatialLite geometry layers that can be viewed and analyzed in QGIS. This is done using Vector ‣ OpenStreetMap ‣ Export topology to SpatialLite.

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  • The Kalyan.osm.db file contains all feature types in the OSM database – Points, Lines and Polygons. GIS layers typically contain only one type of feature, so you need to choose one. Since we are interested in building, here you need to choose Polygon (nodes) as the Export type. You would choose Polylines (open ways) if you wanted to get the road network. Name the Output layer name as Kalyan_building. GIS data has 2 parts to it – location and attributes. We are also interested in the name of the buildings – not just its location, so we need to export that information as well. Click on Load from DB under Exported tags section. This will fetch all attributes from the Kalyan.osm.db file. Check name and building tags. See OSM Tags to learn more about what each attribute means. Make sure the Load into canvas when finished is checked, and click OK.

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  • You will see a new Polygon layer named Kalyan_buildings loaded in QGIS. Note that this contains ALL polygon in the OSM database for the viewport.

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  • To view attribute Right click on Kalyan_buildings layer and select Open Attribute Table.

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  • To save as vector layer. Right-click the Kalyan_buildings layer and choose     Save As….
  • In the Save vector layer as… dialog, enter the name of the output file as Kalyan_buildings.shp. Leave all other options as they are and make sure the Add saved file to map option is checked. Click OK.

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  • You will see a new layer named Kalyan_buildings.shp in the QGIS canvas. Uncheck the Kalyan_buildings layer as we don’t need that anymore.

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The extraction of the Kalyan_buildings shapefile layer is now complete.

 

Download DEM FREE for offline use Earth Explorer

The DEM (Digital Elevation Model) data which represent the ground elevation, can be used for various applications. Here, we will see the procedure to, how to download the DEM data free and which can use for various application.

  • The DEM data can download freely from Earth Explorer website for your AoI

PROCEDURE:

  • To download the DEM data, Open the Internet Explorer
  • Select the URL and type www.earthexplore.usgs.gov/ and click Enter on keyboard

The Earth Explorer website will open. Here, we can search the AOI and download the DEM data

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  • Under the Search Criteria, we search the AOI and give the remaining searching criteria. the window should look as shown below.

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  • It shows the Address of AOI select it and Click on Data Set tab
  • Under Data Set Search, expand Digital Elevation and select GMTED2010

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  • Click on Results tab, to view the available data

You will see the list of available data

  • Click on Download Option

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  • To download, need to Login and click on Download on Download Options window

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The Zip file will download and need to extract the zip file. The DEM.tif file which you can open in any GIS software to view the DEM file.

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This how the DEM data is downloaded and can use for offline analysis for various application.

How to create Anaglyph in ERDAS Imagine

Data Requirement

To create the Anaglyph in ERDAS Imagine, we need:

  • DEM data and
  • Satellite imagery of same area

You may refer ‘Download DEM Data for offline use‘ and ‘Download and geo-refercne imagery for offline use‘ if you are not sure how to get the data.

In this tutorial, satellite image is downloaded from the Google Earth and geo-referenced in QGIS. Geo-referenced image is re-sampled in ERDAS imagine .img format. Here is how it looks:

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Major Step Involved are as below:

  1. Step 1: Import DEM data into img format.
  2. Step 2: Create Painted Relief from elevation grid data
  3. Step 3: Crate Anaglyph and Obverse

Step 1: Import DEM data into img format

Import DEM data into .img using ERDAS IMAGINE file format.

  • Open ERDAS IMAGINE
  • Click on Manage Data tab and click Import Data tool

Import window open set the Import window as shown below:

  • Select the Format as DEM
  • Navigate the Input File to your folder and select .dem file
  • Navigate the Output File to your folder

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  • Click OK

Your DEM file will be save in .img file in your folder.

Step 2: Create Painted Relief from elevation grid data

This step guide you on how to crate Shaded relief using the DEM data or elevation data.

  • Click on the Terrain tab and select the Painted Relief tool

The Painted Relief window open and you will input all required criteria

  • In Input DEM, navigate to your folder and select the GESurface.img (this DEM data)
  • In Output File, navigate to your folder name it PaintedRelief.img
  • Click the radio button of Ignore Zero in Output Stats.

The Painted Relief window should look as shown below:

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  • Click OK

The PainterRelief.img file is saved in your folder and look as shown below6

The Data for anaglyph is prepared. you will create the anaglyph in the ERDAS Imagine.

Step 3: Create Anaglyph and Observe

  • Open the ERDAS IMAGINE if not open
  • Click on the Terrain tab and select the Anaglyph tool

The Anaglyph Generation window open

  • Input DEM, navigate to your folder and select the PaintedRelif.img
  • Input Image column, navigate to your folder and select GEImage.img
  • Output Image column, navigate to your folder Anaglyph.img
  • Change the Exaggeration to 2 (this is to magnify vertical effect)
  • Change the scale Output Scale to 10000

Now the Anaglyph Generation window look as shown below

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  • Accept all other default setting as it is and Click OK

The Anaglyph image is generated and open it on 2D View window of ERDAS IMAGINE and anaglyph image look like as shown below:

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Use your 3D glasses to view the imagery. you should be able to visualize 3D effect of terrain.

Download Open Street Map data in shape file format

There are few ways to download Open Street Map data for offline use in GIS. One among them is to:

  1. Download OSM file of AoI in QGIS
  2. Save as OSM file to XML format
  3. and finally Export xml data in Spatial Lite database as layer.

this is complex way and you need to setup database first. however if you need to download data very frequently you can go for above option. else there is simple way to download data from third party portals. you can download Open Street data directly in ESRI Shape file format for your desire Area of Interest.