The screen grab above was captured during the process of creating a color shaded relief model of Irvine, California. It was created in one of many demos I gave to clients while working for PCI Geomatics and was also used in the following tutorial that I created for the PCI geomatics website.

PCI Geomatics is a world leading developer of image centric geomatics software solutions. The PCI Geomatics flagship software, Geomatica, meets the growing demands of the remote sensing, GIS, cartography, and photogrammetry worlds. PCI Geomatics has long been recognized for offering high-value geomatics software solutions, advanced algorithms, excellent customer assistance, and product support for the widest range of spatial data formats in the industry.

https://tmackinnon.com/wp-content/uploads/3D-CSR-Irvine-California.jpg296358Ted MacKinnonhttps://tmackinnon.com/wp-content/uploads/marker3.pngTed MacKinnon2006-06-24 11:18:122014-06-24 11:31:45Color Shaded Relief Model - Irvine, California

The two images above are of a portion of the small town of Shediac, New Brunswick. Each one is of the same spatial extent, however the one on the left is of an aerial photo of the town (1999) while the one on the right is a color shaded relief model created from high resolution LIDAR data (2003) using PCI Geomatica software. The LIDAR digital surface model (DSM) was part of a LIDAR flood modeling graduate research project.

Shediac is a small town located in eastern New Brunswick approximately 20 kilometers north of Moncton. The town calls itself the “Lobster Capital of the World”, hosts an annual lobster festival every July, and the world’s largest lobster sculpture is situated at the main entrance to town.

https://tmackinnon.com/wp-content/uploads/ortho-lidar-csr.jpg284583Ted MacKinnonhttps://tmackinnon.com/wp-content/uploads/marker3.pngTed MacKinnon2006-06-04 12:06:512014-06-24 12:12:37Color Shaded Relief Model - Shediac, New Brunswick

The two images above represent artificial 3D perspective views from different points of origin featuring color shaded relief models that were created from high resolution LIDAR digital surface models as part of a LIDAR flood modeling graduate research project. The image on the left highlights a highway overpass while the image on the right features a residential area with a large school and a church easily detectable in the LIDAR all hits data set. Bouctouche is a small town located in eastern New Brunswick approximately 40 kilometers north of Moncton where the Bouctouche River meets the Northumberland Strait. It was an important aspect of the research study due to the extreme storm surge flooding that the region experiences every winter.

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.

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.

https://tmackinnon.com/wp-content/uploads/marker3.png00Ted MacKinnonhttps://tmackinnon.com/wp-content/uploads/marker3.pngTed MacKinnon2006-03-26 19:06:022012-03-26 19:08:23Example of an Aspect Map

The slope or the gradient of a straight line within a Cartesian coordinate system is known as the measure of how steep a line is relative to the horizontal axis.

In calculations; it is generally represented by the letter m, and defined as the change in the Y coordinate divided by the corresponding change in the X coordinate, between two distinct points on the line (X1, Y1 and X2, Y2). Since the Y axis is vertical and the X axis is horizontal by convention, slope is often referred to as the rise over the run or the change in the vertical coordinates, divided by the change in the horizontal coordinates.

Basically, the larger the slope value, the steeper the line is. A horizontal line has a slope of 0, a 45 degree line has a slope of 1, and the slope of a vertical line is typically undefined. In trigonometry two lines are considered to be parallel if and only if their slopes are equal or if they both are vertical and therefore undefined. Two lines are considered to be perpendicular if and only if the product of their slopes is -1 or one has a slope of 0 and the other is vertical and undefined.

There are two common ways to describe slope. One method is to use the angle of the slope in degrees (0 to 90), and the other is to represent the slope as a percentage (0 to 100). Expressing slope as a percent is common but can be confusing because a percent slope can be greater then 100%. A 100% slope is actually only a 45 degree angle due to the fact that the rise and run of a 45 degree angle are equal and when divided always equals 1 and when multiplied by 100 will equal 100%.

In terrain modeling we generally model an entire surface and not just one line so we need to calculate the slope of a best fit surface plane (which is made of lines). Because the terrain model is usually continuous across the entire surface, it is important to be able to calculate how to represent grid cells (or pixels) when going from one elevation to the next. To do this we generally need to know the aspect or the direction that the surface plane is sloped as well. Together the slope combined with the aspect of the surface can virtually define the surface plane completely.

In the example shown to the left, a slope map 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 therefore the color white represents a 0 slope and the shades of grey increase through to black which represents an undefined slope. The majority of slopes for this map do not exceed 17 degrees (except for vertical slopes) as this is a relative low lying area of Appalachian terrain.

The image above and to the right is of an actual bedrock cliff with some technical information embedded onto it so it may be used to help better understand slope. The black arrow represents the slope or the measured angle that the rock is dipping towards. The slope in the image would be 45 degrees approximately so the slope would be 1 or 100%. The rise and the run of a slope with a 45 degree angle will always equals 1, thus when multiplied by 100 to calculate percent slope will equal always equal 100%.

The image below is a Slope Model that I derived from a digital elevation model (DEM) of Lismore, Nova Scotia. The values of the slopes of the DEM are represented by a 0-255 grey scale color ramp, therefore the color white represents a 0 slope and the shades of grey increase through to black which represents an undefined slope. The majority of slopes for this map do not exceed 17 degrees (except for vertical slopes) as this is a relative low lying area of Appalachian terrain.

Click here to learn a little more about Slope Models and how the image below was created.

https://tmackinnon.com/wp-content/uploads/lismore-slopes.jpg648624Ted MacKinnonhttps://tmackinnon.com/wp-content/uploads/marker3.pngTed MacKinnon2006-02-25 14:10:272012-03-27 14:16:29Example of a Slope Map

The following images are examples of perspective view models that were generated from a 2 meter LIDAR DEM integrated with 50 cm digital orthophotography of Port Lorne, Nova Scotia. Port Lorne is a coastal community along the Bay of Fundy with a relatively steep terrain so the images represent different perspective views depending on the source of origin and the direction that they are facing.

The colored arrows on the key image to the right represent the different perspective views that were generated from different locations and viewed along different directions (displayed in the images below). This image of the area also represents the traditional GIS view from above, as discussed above.

The first image below represents a perspective view (red arrow) of the area if it were viewed from the center of the image, above the wharf looking in an easterly direction.

The next two images below represents a perspective view (blue arrow) of the area if it were viewed from the upper right hand corner of the original image in a south west direction. The images that demonstrate the same perspective but have different types of LIDAR DEMs integrated with them allowing them to portray different data within them.