Management and inventory of control points using Geographic Information System

Ying Bo Wang¹

¹RMIT University, Melbourne VIC 3001, Australia

Abstract

Surveying companies traditionally store their control point data in separate files and only access this information based on what the staff has remembered about them. GIS provides a potential solution by providing a framework for users to access their past control points in a geospatial context, along with attribute data. This application has been applied to Singapore. Two different pre-existing data sets were used; one is a road network shapefile that functions as a basemap in the GIS while the other is a Microsoft Excel file that provides the attribute data for the control points. Overlaid on top of the road network is a point shapefile that locates where each group of control points are. With this application, users are able to quickly and accurately find control points of interest, with little degradation over time. This application shows how GIS could possibly be used in the more general area of asset management, especially assets with a spatial component.

Keywords: Singapore, Control Point, Geographic Information System, Geospatial, Asset Management, GIS, ArcGIS

Introduction

In the surveying industry, it is important to know where the previously established control points around a job site are, as it would allow surveyors to use these control points to do their surveys without the need to setup new ones. This will lead to a reduction of pre-survey work and would expedite the surveying workflow. In Singapore, this is especially critical as the land area is only 714.3 square kilometres for the entire country (Land Transport Authority 2013). For companies that have done years of surveying work, an overlap of a new job site with old job sites is practically a given.

In the past, the method to store and retrieve information regarding the location of the control points was done by pure rote memorisation. Over the years however, it is difficult to remember all the jobs performed at various locations around the country. This is further exacerbated by the fact that there will be turnover in staff, which inevitably leads to loss of such information. This has led to cases where the field surveyors have forgotten or remembered wrongly where their old control points were and they have had to create new control points, only to find their old control points afterwards. This was a case of wasted man-hours and resources that a company, J K Foo Consortium Pte Ltd., wanted to address.

Geographic Information Systems (GIS) is appropriate in this situation as all the control points have an inherent location. In fact, all the control points have coordinates in the SVY21 co-ordinate system, making it simple to place them on the same layer. While all the control points are on the same layer, it is easy to locate the control points of interest (those near the current job site) by eye. Everything up to this point could still be done with a paper map. But a GIS provides additional functions not possible with a paper map. GIS allows attribute data to be attached to the spatial data. This allows the user to perform spatial or logical queries to return the control points the user requires.

The purpose of this assignment is to discuss the utilisation of GIS to manage surveying control points. The application chosen is an ArcMap Document (.mxd) file that contains two layers, a shapefile layer that contains all the jobs and a basemap layer. The product is a shapefile layer created and accessed using ArcGIS. The shapefile could also be read with other free GIS, like Quantum GIS (QGIS) or ArcReader. This shapefile contains the jobs’ locations that a surveying company undertook in its years of business in Singapore. Each job entry in the shapefile would be given a coordinate from a representative control point. Further exploration of a particular entry would lead to additional information related to the job. This was accomplished with hyperlinks in the shapefile. This assignment also looks at the methodology to produce products needed and discusses the limitations of such an application.

Material and Methods

Data

The data set used consists of a basemap shapefile and a Microsoft Excel document. The shapefile contains the street network of Singapore, dated around 1997. It had no attribute data, just a collection of lines. This data was produced and owned by J K Foo Consortium Pte Ltd as a product of one of their past jobs for Singapore Land Transport Authority. The road network was produced in SVY21 coordinate system. Heywood, Cornelius and Carver (2006) state that ‘The purpose for which a spatial data set has been created will influence the quality and spatial detail provided by the data set.’ As this shapefile only consists of the road network, it did not cover the forested areas, nature reserves, water bodies, airports and military camps of Singapore. Thankfully, as Singapore was highly urbanised, with public roads covering roughly 5 kilometres per square kilometre of the land area, this was not a big impediment (Land Transport Authority 2013). This road network shapefile, shown below in Figure 2, was used as a basemap layer of Singapore. Users are expected to be able to identify the various addresses of Singapore through their knowledge of the road network shape. This could be supplemented by using a road directory map book.

Alternatively, it was considered to buy an updated vector shapefile of the roads from Singapore Land Transport Authority or Singapore Land Authority. It was also possible to buy a raster layer of Singapore. Other data sources considered include satellite images and aerial photographs. However, these options were mooted by the company as they felt the road network they possessed, combined with their expert local knowledge and the onemap.sg website, was sufficient to locate all locations in Singapore. The company felt there was no need to spend additional resources to procure a more complete basemap.

The Microsoft Excel document was the surveying company’s file that contains all the necessary attribute data related to their jobs. This includes Job Number, Lot Number, Road Name, Client, and etcetera. This document will provide the attribute data that will be linked to the spatial locations of each job location.

Methodology

The company only had one copy of ArcMap 10.0 that can create and edit the shapefile and attributes. ArcReader, a free version of ArcMap, was used by other members of the company to view the application. This meant that after every new edit of the job shapefile, the user would have to publish a new Published Map Documents (.pmf) file for use with ArcReader.

Figure 1: Concept behind application

The road network shapefile was originally designed for viewing in ArcView3.1. Some steps were taken in ArcCatalog to ensure the road network shapefile could be used in ArcMap 10.0. This road network layer would be used as the basemap. Next, a new vector point shapefile was created to display the locations of each job, as well as list out the various attributes associated with each job. Each record was located on the basemap and given a Job Number attribute. Conceptually, this is shown above in Figure 1. Following that, a join operation was performed in ArcMap to link the Microsoft Excel file with the spatial locations of the jobs. The key used to join them was the Job Number field.

The data model used in this application was a vector shapefile. Chang (2012) states that discrete spatial features are represented as points, lines and polygons using points with x-, y-coordinates in the vector data model. The data generated in this application were discrete points with coordinates, which makes it suitable for the vector data model. The alternative would be to use a raster layer. If a raster layer was used, it would bring up several issues. Firstly, the spatial resolution of each cell in the raster layer would have to be determined. This presents its own questions as how to handle multiple jobs within the same cell. Secondly, each time the raster layer had to updated, the user would have to locate the correct cell, and then edit the raster data in a different window. Overall, a vector data model is easier and more efficient for this application as the data is discrete in nature.

Additionally, a Hyperlink attribute was added to the Job Location shapefile. This would allow any user to access additional information related to the job. Finally, when the user was satisfied with editing, he/she would create a .pmf file to be distributed among the company’s internal server for all employees of the company to view the application on ArcReader. The final application displayed would be similar to Figure 2 below.

 Figure 2: Road network of Singapore with example control points, displayed in ArcMap 10.0

Results

Upon opening the application, any user would be able to locate his/her new job site and recognise which of the old job sites nearby could be of help to him/her. LeBoeuf, Dobbins and Abkowitz (2003) had asserted that ‘certain relationships and operational trends are more easily conveyed in a geographic context than in a traditional tabular format’. In this case, a field surveyor not familiar with the area could look at the map and visually identify locations, rather than using text addresses that held no significance to the surveyor. Information about the old job sites could be found out by using the Identify tool in ArcReader. The user could also drag a box around multiple features to obtain their attribute information.

Figure 3: Identify window for a job entry in ArcReader

The user could also perform a search or a logical/spatial query to return the jobs he/she was interested in. This was done using the Find tool. Specifically, the most common query is to perform a search in the Road Name field of the control point layer. The user would put in a search that would return all job entries that matched the road name the user typed. From there, the user would be able to zoom in to the location of interest. A similar query could be done in the other fields, assuming the user had expert knowledge on what was required. The user could also input a specific X, Y coordinate and pan to that location to search for nearby jobs.

Additionally, the user could use the Hyperlinks tool to link to folders on the company’s servers. This allowed the user to jump to the folder containing a list of coordinates of all the control points used for this particular job, control point sketches, photographs and related documents for the job.

Discussion

With the current application, users can find, identify and use hyperlinks to job locations of interest. This must all be done at a local workstation. The next step would be to develop a mobile product, such that users can access this application even out in the field. Within the ArcGIS 10 System, there is the ArcGIS Server product that could be utilised for this purpose. Alternatively, an offline product could also be developed, so that field surveyors need not have internet connection to access this information. With a wide-screen tablet, it should be feasible to use this application on the move.

To add context to the map, it would be useful to have other thematic layers. This could be an elevation raster layer, a vegetation cover layer or a buildings layer. The elevation layer would be a Digital Elevation Model (DTM) or a Triangulated Irregular Network (TIN). It would provide slope and aspect of the land. The vegetation layer would show where the forests and nature reserves are. The buildings layer would contain polygons representing buildings with a height value attribute for each polygon. All these additional layers would help the field surveyor to plan his survey.

With the current extent of technology, GIS is the premier method, with regard to time and cost, to manage large amounts of spatial data. Within this application, GIS will consolidate the company’s knowledge about control points and would be able to disseminate this information to multiple users with little downtime. The disadvantages of using GIS in this case would be (i) its dependence on Intranet availability; users must be connected to the company’s servers to use Hyperlinks, and (ii) a technological divide; some users might not know or like using a digital service for their needs.

Additionally, it is possible to map directly all the control points. This way, users would directly see all the control points, instead of needing to open a list of coordinates and place the multiple control points manually. However, with multiple control points per job, this would increase the work needed to update the shapefile each time. Generally, the control points are not too far from the job site itself, so it is a minor concern and not considered worth the extra effort.

Conclusions

The application developed is able to find, identify and use hyperlinks for jobs of interest. From there, the user can quickly find more information relating to the control points. Cheng and Phillips (2011) assert that GIS is capable of presenting geo-referenced information which firms can utilise for more informed decisions. This GIS application accomplished that, helping the company’s management to decide whether it was necessary to create new control points or just use the existing control points. Its main disadvantages are the Intranet requirement and users’ lack of knowledge or reluctance to use this application. Possible future improvements to this application include an offline mobile version and additional thematic layers.

Acknowledgement

The author acknowledges J K Foo Consortium Pte Ltd for their input and advice in developing the application. The author also acknowledges Ms Gita Pupedis on her thoughtful comments on this assignment.

References

Chang, K 2012, ‘Introduction to geographic information systems’, 6^th edn, McGraw-Hill, New York, USA.

Cheng, L & Phillips, J 2011, ‘Geographic information system applications in supply chains’, International Journal of Business Research, vol. 11.5, p131-136.

Heywood, D, Cornelius, S & Carver, S 2006 ‘An introduction to geographical information systems’, 3rd edn, Prentice-Hall, Harlow, UK.

Land Transport Authority 2013 ‘Singapore Land Transport Statistics in Brief 2013’, viewed 23 Sep 2013, http://www.lta.gov.sg/content/dam/ltaweb/corp/PublicationsResearch/files/FactsandFigures/Stats_in_Brief_2013.pdf

LeBoeuf, EJ, Dobbins, JP & Abkowitz, MD 2003 ‘Development of a GIS-based Spill Management Information System. Phase I: Proof of Principle Approach for the Cheatham Reach’, Vanderbilt University—Civil and Environmental Engineering, Nashville, TN.