A digital elevation model (DEM) or sometimes referred to as a digital terrain model (DTM) is a quantitative representation of the topography of the Earth (or sometimes other surfaces) in a digital format. They are a common component of geographic information systems /remote sensing and are usually represented by cartesian coordinates and numerical descriptions of altitude. In contrast with topographical vector maps, the information is stored in a raster format. That is, the map will normally divide the area into a rectangular grid of cells or pixels and store the elevation of each one as a DN value.

Traditionally most common DEMs used in the Geomatics industry only contain elevation values of the true ground’s surface but DEMs can also sometimes contain other features found upon the ground’s surface as well. When it contains all features it is often referred to as a digital surface (DSM). Digital surface models contain elevation values representing the ground as well as any other objects such as buildings and trees.

The resolution of the DEM, or the distance between adjacent grid points (often the size of the cell or pixel), is a critical parameter in determining the amount of detail that a user should except to represent in the DEM. The smaller the resolution, the more details or features that will be present, e.g. a 1 m resolution DEM will contain more details then a 20 m one and be better suited for hydrological analyses.

DEMs are used as a source of elevation (and to create other digital terrain models) for many different purposes such as:

• to orthorectify imagery
• as a source of topographic information and to create contour lines from
• to identify geological structures in topography
• to identify risk areas and hydrological flow patterns
• to identify flood risk areas
• to determine accessibility
• to identify regions of visibility for radio or cell towers
• to predict how the terrain can effect signal strength and reflection
• and many more uses

Digital elevation models may be prepared in a number of ways, but they are frequently obtained by remote sensing rather than direct survey. Older methods of generating DEMs often involved interpolating digital contour maps from aerial photography produced by direct survey and interpretation of the surface.

Many mapping agencies produce their own DEMs, often of a higher resolution and quality, but frequently these have to be purchased, sometimes at considerable cost. The two methods of creating DEMs that are covered on this web site deal with LIDAR and Photogrammetry methods.

• MacKinnon E (2003) Surface Modeling and LIDAR Validation Middleton, Nova Scotia: Applied Geomatics Research Group, Centre of Geographic Sciences, 49 pages
• MacKinnon E, Sangster F & Hynes D (1999) Makkovik, Labrador – 3D modeling and Data Integration presented at the Bedford Institute of Oceanography in Dartmouth, Nova Scotia

Sometimes commonly known as quantitative geomorphology, digital terrain modeling is thecomputer processing of raster grid arrays of elevation data. Using Geographic information system (GIS) technology we can further enable terrain-modeling results to be combined with non topographic spatial data creating several value added products.

Terrain Models are derived from data represented by digital elevation models (DEMs) and can include shaded relief models,
slope and aspect models, perspective scene generation, and drainage basin analysis (and other models).

The physiogeographic characteristics of a surface can often be determined by elevation, slope, and its orientation, or aspect. Together they can virtually define the surface plane completely, and provide valuable information for land use planning and other aspects of geomatics.

Traditional images in geomatics are often two dimensional, meaning that all data in the image can be referenced by X and Y coordinates. Three dimensional images (3-D) incorporate a third dimension (the Z component) which represents the elevation or depth aspect of the data. To incorporate it into an image requires creating special geomatics value added products that allow users to perceive the presence of the third dimension into a traditional two dimensional setting
(because most paper and computer screens are flat or two dimensional).

In GIS applications it is often beneficial to add a texture component to the spatial data that will help the user get a feeling for the vertical depth of the data by emphasizing the elevation. To do this you need to create a shaded relief model from the DEM to model into the data.

Shaded relief models use a defined light source at a fixed location it indicate terrain displacements using a shadow effect from evaluating the aspect and slope relative to the light’s azimuth angle and altitude achieved with varying grey scale tones resulting in the darkening of one side of terrain features, such as hills and ridges (the darker the shading, the steeper the slope).

The shadow direction is affected by the light’s azimuth setting and shadow length is affected by the altitude component. The models provide subtle shadings which we naturally perceive as depth, helping to make the image look three dimensional. A drawback with this type of model is that depending on the placement of the illumination source, the eye and brain often see different things. Adding color to the shaded relief images utilizes chromo stereoscopic techniques to help emphasize the depth of the Z dimension of the data.

Color shaded relief models (CSR) are usually graded with a pseudo color ramp from cooler (darker) colors representing
lower elevations to warmer (brighter) colors depicting greater elevations. Most imagery and data that we view in geomatics is typically viewed vertical downwards toward the map or image. Occasionally it is useful to change that default traditional view because additional topographic information can often be revealed by observing the same elevation data obliquely (commonly known as a three dimensional perspective view). Data integration and overlays are very common with perspective views because it allows traditional flat images to become new products by incorporating an elevation component and providing a new look at the same data.  It is also probably used more so for visual appeal then as another method of extracting data.

The image above and to the left is a perspective view of a color shaded relief created from high resolution LIDAR using PCI Geomatica software. The oblique angle view point looking down at the image allows the observer to easily identify many of the data’s features such as trees, cars and buildings.

The perspective scene in the image on the left is a representation of an urban terrain model including buildings and other various features. It was created using ESRI ArcScene software and high resolution LIDAR digital point data. The artificial oblique view allows the observer to obtain a unique glimpse from above looking down in a southerly direction towards City Hall of downtown Toronto, Ontario.

More information on Terrain modeling and examples

• MacKinnon E (2003) Surface Modeling and LIDAR Validation Middleton, Nova Scotia: Applied Geomatics Research Group, Centre of Geographic Sciences, 49 pages
• MacKinnon E (2004) Three Dimensional Flood Modeling with High Resolution LIDAR (Graduate Thesis) Middleton, Nova Scotia: Applied Geomatics Research Group, Centre of Geographic Sciences, 200 pages
• MacKinnon E (2005) Three Dimensional Flood Modeling with High Resolution LIDAR (2005 CIG Conference Proceeding) Ottawa, Ontario:Canadian Institute of Geomatics, 8 pages
• MacKinnon E, Sangster F & Hynes D (1999)  Geological Data Integration: Makkovik, Labrador Lawerncetown, Nova Scotia: Centre of Geographic Sciences, 12 pages
• MacKinnon E (2004)  3D Modeling with High Resolution LIDAR - presented at the GeoTec Conference in Toronto,Ontario and displayed at the Applied Geomatics Research Group in Middleton, Nova Scotia
• MacKinnon E (2004)  Bouctouche, NewBrunswick – Color Shaded Relief - presented at CCAF annual general meeting held at the University of Moncton in Moncton, New Brunswick, and displayed at the Applied Geomatics Research Group in Middleton, Nova Scotia
• MacKinnon E (2004) FLood Simulation Modeling with High Resolution LIDAR - presented at CCAF annual general meeting held at the University of Moncton in Moncton, New Brunswick, and displayed at the Applied Geomatics Research Group in Middleton, Nova Scotia
• McCurdy C, MacKinnon E & Lynds T (1999) Integration of Digital elevation Models and Imagery : Terrain Analysis of the Antigonish Highlands  - presented at the Center of Geographic Sciences in Lawrencetown, Nova Scotia

• Digital Elevation Models (DEMs)
• Shaded Relief Models
• Color Shaded Relief Models (CSR)
• Creating a CSR model in Geomatica v9.1
• Slope Models
• Aspect Models
• Perspective View Models

The site has evolved slightly with a few functions or sections being added to it as time went on but it has always been primarily used to promote the Canadian GIS industry and to share information with other Canadians that also have an interest in GIS. It also went well together with GISjobs.ca, another GIS site that I created to help Geomatics students find Canadian GIS jobs much easier. GISjobs.ca turned out to be a real success and eventually led to the creation of GoGeomatics, a Canadian Geomatics job board site that allowed people to post GIS jobs for free.

CanadianGIS.com helps provide people with resources about Canadian GIS data, basic information about Canadian companies that provide GIS services, locations of Canadian data and maps, information about GIS events, places to find Canadian GIS employment and education info and many other great resources. Content for the site been created by me and a few volunteers with some has also been supplied by various GIS companies and academic institutions.

If you have not yet checked the site out then I encourage you to go and see for your self, and if you discover that there is information related to Canadian GIS resources that I have missed then please do let me know. – Join the Canadian GIS LinkedIn Group 

 regards,

Ted MacKinnon -Geomatics Specialist

tmackinnon.com

Contact Me: email

Twitter: tedmackinnon

LinkedIn: tedmackinnon

FaceBook: ted.mackinnon

Included below on this page is the report written for this project, a presentation that covered all aspects of the project and more general information and links about GIS mobile mapping. The report includes all code used in designing the ArcPad application (visual basic, XML etc). The presentation was presented at COGS in Lawerncetown, Nova Scotia during the fall of 2003. The existing AGRG weather station network now consists of 14 tripods and 1 tower setup (as of Aug 2004).

Basic overview of Mobile Mapping

When you combine global positioning systems (GPS) and geographic information system (GIS) technology together you get a powerful tool better known to most in the Geomatics industry as Mobile Mapping. This combined technology allows users to visualize information with existing digital data, record new information exactly directly at the source, and interact directly with the world around you.

Over the past few years the main process of collecting field data included gathering and using information with a paper-based process that quite often involved a lot of data entry without access to real-time information. The recent advancements in GIS and GPS technologies have changed many of the field-based information gathering processes and increased the efficiency and accuracy with which field users collect and use spatial information.

There are several different software and hardware combinations suitable for mobile mapping tasks that are currently available and range from simple inexpensive to more complex setups. This page will use ESRI ArcPad as an example due to the relative experience I have had with this over the past few years. But do keep in mind that there are many more different ones out there and one should experiment to find the setup that best fits their project needs.

ESRI ArcPad software combines database access, mapping, GIS, and GPS integration when you are in the field via a handheld computer device. The main advantage to this is that you can incorporate your existing data such as database, vector and raster images along with the data that you collect. The following are some of the many functions that are possible with mobile mapping:

- Move around your map with navigation tools including zoom and pan, and center on the current GPS position.
- Query your data: Identify features, display hyperlinks, and locate features.
- Measure distance, area, and bearings on your ArcPad map.
- Navigate with your GPS: Connect a GPS and let ArcPad guide you.
- Edit your data: Create and edit spatial data using input from the mouse pointer, pen, or GPS.

The user can output existing data from a GIS project to use with the mobile unit in the field and then input the new data into the same project file in their GIS when it is completed. This function known as “disconnected editing” is great for updating an existing database and project with out having to create a new every time. It also allows the user to bring a subset of the data that they need and not the complete data sets, allowing them to save disk space and making it possible to use with a hand held unit. Customization of ArcPad is done using the ArcStudio program. All customization is performed on the PC and deployed to ArcPad on the mobile device. Some of the customizations possible are

- Creation of new toolbars with built-in and custom tools.
- Design of custom forms to streamline data collection in the field.
- Write scripts that automate tasks and interact with ArcPad software’s internal objects.
- Build applets to accomplish your organization’s unique

More information on ESRI ArcPad can be found in the ESRI white paper titled ArcPad™- Mobile Mapping & GIS

2003 Mobile Mapping Related Documents & Links

• MacKinnon E (2003) Mobile Mapping Application for Updating AGRG Weather Station data Middleton, NS: Applied Geomatics Research Group, Centre of Geographic Sciences, 27 pages
• MacKinnon E (2003) Mobile Mapping Application for Updating AGRG Weather Station data presented at the Applied Geomatics Research Group, Centre of Geographic Sciences; Middleton, Nova Scotia
• MacKinnon E (2003) Leica GS20 Professional Data Mapper – AGRG Users Guide Middleton, NS: Applied Geomatics Research Group, Centre of Geographic Sciences, 31 pages

• Mapping Directory
• Mobile GIS brings instantaneous information to users in the field
• Mobile and Field GIS Software Links
• ArcPad6- Mobile Mapping and GIS
• ArcPad – Surveyor
• ArcPad product description

GIS Spatial Modeling is the process of modeling, examining, and interpreting geographic data.It uses a set of defined methodology and analytical procedures to derive information with spatial relationships between geographic phenomena. It can be useful for evaluating suitability and capability, for estimating and predicting, and for interpreting and understanding real world situations. There are four traditional types: spatial overlay surface analysis, linear analysis, and raster analysis.

Data with spatial relationships can be modeled in a GIS to provide images and relationships that can be interpreted to help solve problems and provide information in a way that data bases by them selves can not. The image to the right for example is a screen capture of a GIS thematic spatial model created from a database of precipitation measurements from various weather stations and data loggers spread out across the region. ESRI Geostatistical Analyst was used to create a model that can be easily used to depict the amount of precipitation that a community in the region would experience based on the data from the databases.

Spatial Modeling Examples

Below are two presentations that I gave on GIS Spatial Modeling, one is an informal more information based one that was used to train other students how to use the ESRI Geostatistical Analyst extension and the other is a more formal presentation that was open to all students and faculty at the campus.

• MacKinnon E (2003) Mobile Mapping Application for Updating AGRG Weather Station data (actual ppt presentation) Middleton, NS: Applied Geomatics Research Group, Centre of Geographic Sciences, 24 slides

•  MacKinnon E (2003) Mobile Mapping Application for Updating AGRG Weather Station data (presentation which was part of a lecture used to train fellow GIS students)
  Middleton, NS: Applied Geomatics Research Group, Centre of Geographic Sciences, 33 slides

Basic overview of Spatial Data base design

The second part of the project was focused on generating a GIS spatial database of the vegetation found within each campsite that was collected during a Rapid Vegetation
Assessment (RVA) Survey.

If you do not fully understand the fundamentals of spatial database design and management, then you may never unleash the power of GIS. Behind almost all colorful maps that you see around is a complex data management framework and structured spatial data that required special attention to issues of scale, accuracy and projection issues.

A database can be defined as a collection of interrelated information or data, managed and stored together as a collective unit. A GIS spatial database is a database that includes collections of information about the spatial location, relationship and shape of topological geographic features and the data in the form of attributes.

The design of the spatial database is the formal process of analyzing facts about the real world into a structured model. Database design is characterized by the following phases: requirement analysis, logical design and physical design. In more common terms, you basically need a plan, a design layout and then the data to complete the process.

Having a solid well designed spatial database is the key to performing good Spatial Analysis. The database can be complex and designed with expensive sophisticated software or can be merely a simple well organized collection of data that can be utilized in a geographic form.

Three main categories of spatial modeling functions that can be applied to geographic features within a GIS are: (1) geometric models, such as calculating the Euclidean distance between features, generating buffers, calculating areas and perimeters, and so on; (2) coincidence models, such as topological overlay; and (3) adjacency models (path finding, redistricting, and allocation). All three model categories support operations on spatial data such as points, lines, polygons, tins, and grids. Functions are organized in a sequence of steps to derive the desired information for analysis.

Examples of GIS Spatial Database and Modeling

• MacKinnon E (2004)
  
  Spatial GIS Vegetation Database and GIS Spatial Modeling for the Jeremy’s
  Bay Campground of Kejimkujik National Park and Historic Site.

GIS operates on many levels and over the past decade has become an essential tool for most urban and resource planning and management organizations. On the most basic level, GIS can be used for simple digital cartography, to create various types of maps.

However the real power of GIS is through its abilities to use both spatial and statistical methods to analyze attribute and geographic information together. The end result of such an analysis can be vast amounts of derivative information, interpolated information or prioritized information.
Geographic information systems commonly known as GIS has become a rapidly growing technological field that allows
Geomatics Specialists to solve and model real world situations by incorporating digital spatial and associated tabular data. It is often defined as a comprehensive computerized information system made up of hardware, specialized software, spatial data and people to help manipulate, analyze and present the information used for storing, manipulating and analyzing spatially indexed information.

GIS technology can be used for scientific investigations, resource and utilities management, modeling,  assessments, development planning, cartography and route planning and many other applications.. Some of these and other aspects of the GIS field are currently covered on this web site including projects related to spatial database modeling, Geostatistical spatial modeling, mobile mapping, cartography, and interactive web mapping.

Below are some examples of GIS from a few of the many GIS based projects that I have been involved with over the past few years. The links are to PDF versions of papers, presentations and or manuals related to GIS, I have many more, if anybody is interested in a particular topic then feel free to let me know, as I may have a document available related to that topic.

Examples of GIS

• MacKinnon E (2004) Spatial GIS Vegetation Database and GIS Spatial Modeling at Kejimkujik National Park and Historic Site.
• MacKinnon E (2003) Mobile Mapping Application for Updating AGRG Weather Station data
• MacKinnon E (2003) Mobile Mapping Application – for Updating AGRG Weather Station data
• MacKinnon E, & Murphy J. (2003) Leica GS20 Professional Data Mapper – Leica GS20 AGRG Users Guide

.

• GIS Directory
• GIS Dictionary
• What is GIS – power point presentation with more information about GIS
• GIS Theory - an Overview of GIS by The University of Melbourne
• GIS.com GIS portal site by ESRI
• Geomatica GeoCapacity
• Spatial Databases – models of reality

Cartography | Basic Overview

A map utilizes a variety of colors, symbols, and labels to represent actual features and provide information on their existence, location, and the distance between them. It can also indicate variation in terrain, heights of natural features, and the extent of vegetation cover.

Maps often function as visualization tools for spatial data which is acquired from actual measurements and can be stored into a database, from which it can be later extracted for a variety of purposes. Current trends in this field are moving away from traditional methods of map making and toward the creation of increasingly dynamic, interactive maps that can be manipulated digitally, often known as
Web GIS.

Most maps will contain a scale parameter that will allow the user to convert distance on the map to distance on the ground or vice versa. The ability to determine distance on a map, as well as on the earth’s surface, is an important factor in GIS and the spatial relationships between features. Other important key elements or features that you should find on a good map would be a title, a data frame, a legend, a scale bar, a north arrow, and citation information such as the date, the creator, projection, overview map location etc.

 The Map on the right is a to scale representation of one of the camp grounds located at Kejimkujik National Park

in Nova Scotia. It was created from survey data collected with a Leica RTK system and a Leica Total Station. The legend is hard to see in this screen grab (actual map poster was 2ft by 4ft) but the red line represents the road, dotted lines are trails and the green polygons are the actual camping plots.

Below are some examples of Maps that I have generated for various projects that I have worked on or have had some involvement in, included are the date and the title of the map with a brief description. Clicking on the link will open up an image of the map with some details about the project (Note: most of these maps were plotted out on large paper sheets for display so some details were lost while generating these miniature image versions for the web site – also some of these are still on display at various places).

Examples of Cartography & GIS Map Products

• MacKinnon E (2000)  8th International Marathon Canoe World Championship Site Map - designed for the International Marathon Canoe World Championship that were held in Dartmouth, Nova Scotia
• MacKinnon E (2003)  AGRG Annapolis Valley LIDAR Ground Validation Campaign - presented at the Geomatics Atlantic 2003 Conference held at Acadia University in Wolfville, Nova Scotia and posted at the Applied Geomatics Research Group seminar room in Middleton, Nova Scotia
• MacKinnon E (2003)  Jeremy’s Bay Campground, Kejimkujik National Park - campground was surveyed in 2003 and mapped for Parks Canada  MacKinnon E (2003)
  Jim Charles Loop of Jeremy’s Bay Campground, Kejimkujik National Park - campground was surveyed in 2003 and mapped for Parks Canada  MacKinnon E (2003)
• New Brunswick High Precision Network and AGRG 2003/2004 LIDAR Zones - presented at the Geomatics Atlantic 2003 Conference held at Acadia University in Wolfville, Nova Scotia and used during the ground validation survey in New Brunswick

Cartography Directory

 

 

 

 

• International Cartographic Association (ICA)
• Map Projections
• Google online maps with spatial search capabilities
• Map Quest online maps with detailed directions
• MSN Virtual Earth – Microsoft version of Google Map
• Web Cartography

In digital terrain modeling the Aspect of a surface refers to the direction (azimuth) to which a slope face is orientated. The aspect or orientation of a slope can produce very significant influences on it, so it is important to know the aspect of the plane as well as the slope. Together the slope combined with the aspect of the surface can virtually define the surface plane completely in digital terrain modeling.

Aspect is measured in degrees (similar to a compass bearing) clockwise from magnetic north. A surface with 0 degrees Aspect would represent a north direction, an east facing slope would be 90 degrees, a south facing slope would be 180 degrees and a west facing slope would be 270 degrees.

The example shown  to the left (for larger image click here) is a raster aspect model of Lismore, Nova Scotia was derived from a  digital elevation model (DEM) calculated using PCI Geomatica remote sensing software. It is represented with a grey scale color ramp and helps to indicate what direction slope faces are orientated.

The image above is of an actual bedrock cliff with some technical information embedded onto the image to help better understand slope and aspect relationships. The black arrow represents the slope or the measured angle that the rock is dipping towards.

The aspect is the orientation that the arrow (slope) is pointing with respect to North, therefore the aspect for this slope would be in an easterly direction and often represented by 90 degrees. The blue arrows represent the X, Y and Z dimensions that the combination of both the slope and aspect would use to represent the terrain features.

]]> http://tmackinnon.com/aspect.php/feed 0 http://tmackinnon.com/aspect-lismore-example.php http://tmackinnon.com/aspect-lismore-example.php#comments Mon, 27 Mar 2006 00:06:02 +0000 tmackinnon http://tmackinnon.com/?p=843 The image below is an Aspect Model that I derived from a digital elevation model (DEM) of Lismore, Nova Scotia. The aspect values of the slopes of the DEM are represented in the model by a 0-255 grey scale color ramp. Click here to learn a little more about Aspect Models  and how the image below was created.