012] Global Mapper - Terrain Information Lines: Calculate Elevation/Slope Stats

Today, we will learn how to extract terrain information using Line features.

To follow along, please open the data file we used in the previous session.

1. Extracting Terrain Information for a Line

The process is identical to the one we used for polygons. We will use the same tool to analyze the terrain along our "Road" feature.

1. Select the Road line using the Digitizer Tool.

2. Right-click and select Analysis/Measurement -> Calculate Elevation/Slope Stats for Selected Feature(s)....

3. A dialog will appear asking if you'd like to create new point features at the minimum and maximum elevations. Choose your preference (Yes to add points, No to just calculate).

If you select "Yes," points will be generated on your map showing the exact locations of the highest and lowest elevations along that line.

2. Understanding Line-Specific Statistics

The Feature Information window will now display the results. While similar to the polygon results, there are several key items specific to line features.

Key Statistics Explained for Lines:

1. MAX_UP_SLOPE_DEG/PCT: The steepest incline (uphill) encountered along the path.

2. MAX_DOWN_SLOPE_DEG/PCT: The steepest decline (downhill) encountered along the path.

3. ELEV_GAIN_M/FT: The total cumulative elevation gain (sum of all uphill segments).

4. ELEV_LOSS_M/FT: The total cumulative elevation loss (sum of all downhill segments).

5. LENGTH_3D: The actual 3D distance of the line, taking the terrain's rises and falls into account.

Note on Direction:

In Global Mapper, lines have a direction. The Start point is marked in Green, and the End point is marked in Red when selected. "Up" and "Down" are relative to moving from the green point to the red point.

In this example, the ELEV_GAIN is 26.91m and the ELEV_LOSS is 16.94m. This means that while traveling from the start to the end, you climbed a total of 26.91m and descended 16.94m. Consequently, the end point is approximately 10m higher than the start.

3. Review: Using Path Profile

Let's visualize this data using the Path Profile tool we covered previously.

1. With the line selected, right-click and select Analysis/Measurement -> PATH PROFILE - Generate Path Profile Along Line(s)....

A cross-section of the terrain along the line will appear. The yellow dots at the bottom represent the vertices (corners) of the line.

The default view might show a lot of empty space below the terrain. Let's adjust the settings to focus on the relevant elevation.

2. Go to Path Setup -> Path Profile Settings....

3. In the General Settings tab:

   • Elevation Range: Check Clamp Bottom Displayed Elevation to and enter 75 (meters).

   • Guidelines: Check Draw Reference Line at and enter 90 (meters).

   • Click OK.

Now, the unnecessary bottom space is removed, and a clear reference line is added at 90m.

This analysis is incredibly useful for evaluating hiking trails, bicycle paths, or planned road routes. If you have multiple potential paths from point A to point B, comparing the total elevation gain and loss will tell you which route is the easiest or most challenging.

That’s all for today!