GeoTalks Express: Coastal Flood Analysis using Global Mapper – Questions and Answers

The latest session in Blue Marble’s ongoing webinar series, GeoTalks Express, covered flood analysis in Global Mapper with a focus on identifying impacted areas. Many questions were asked to our presenters during the live session, and while some were addressed during the webinar, we have compiled the questions and answers on coastal flood analysis using Global Mapper below.

Will there be a recording of this webinar?

Yes, GeoTalks Express webinars are recorded and posted to the Blue Marble Geographics YouTube channel. All registered attendees will receive an email with the link to the recorded session; if you did not register for this webinar, sign up here to gain access to all the recorded GeoTalks Express webinars. 

I see during the visualization that the color bar is not changing. isn’t it?

In the animation of tidal water models, the pink flood areas are vector features drawn over the static terrain surface. The shaded elevation data is not altered by the Simulate Water Level Rise tool and will not change as the generated layers are displayed on top of it. 

How then to show sea level variations?

Sea level or bathymetric surfaces can be captured in elevation data and displayed as an elevation grid in Global Mapper. The elevation model used in this webinar clamped the ocean areas to the reference elevation of zero and the Simulate Water Level Rise tool created new vector features based on the surrounding coastal elevations. 

How does Global Mapper realize that e.g. the lake in the southern part is not flooded (still blue), because it might be protected with an embankment?

The Simulate Water Level Rise tool works by expanding the flooded area pixel-by-pixel across the terrain model. When a change in elevation from the reference water level height is greater than the water level rise and smaller than the depression fill depth, the flow analysis continues. If a larger change in elevation is encountered, like an embankment, the flow is terminated. Since the coastal area surrounding the lake rises to an elevation of about 4.5 ft, the flow is terminated before reaching the lake. 

Is there a method to subtract the difference in the flooded area from the zero elevation? 

The Simulate Water Level Rise tool creates vector features that show the extent of the flooded area. For a difference calculation with the terrain model, per-vertex elevation values can be applied to the Water Level Rise layer, and the data can be gridded. With two grid layers, terrain and flood, the Combine/Compare Terrain Layers tool can be used with a subtraction method in order to generate a difference grid. 

When you hover over the map, a white transparent box shows up that shows the name of the layer and height; where is that setting?

This visualization is called Info Tips. Info Tips can be enabled and configured with options from the View menu. The information displayed can be customized to name layers, elevation, specific attributes, and so on. 

Can we export the animation? Can that GM animation be exported as a video? 

The layers shown in the animation are individual vector layers that can be exported to any supported vector format. The animation is only a visual tool in Global Mapper but could be screen recorded using a screen capture program. 

You mentioned Global Mapper Pro for this webinar.  Will Global Mapper Standard also apply?

Global Mapper Standard includes the Simulate Water Level Rise tool, Animation, and the terrain display used in this webinar. The only Global Mapper Pro feature shown was the interface Script Editor. 

Is scripting supported only with the Pro version?

Global Mapper Script is supported by both Global Mapper Standard and Global Mapper Pro. In either of these versions, a script can be written in a text editor program and run outside of Global Mapper or within the interface with the Run Script option found in the File menu. 

The Script Editor, an interface tool for creating scripts, is a Global Mapper Pro tool. This tool allows users to write and edit scripts in a text editor built in to Global Mapper Pro. Additionally, Python language scripting is only available in Global Mapper Pro. 

Will the script run faster than processing the flood simulation in the analysis tool on the screen?

The actual processing done by Global Mapper will not execute any faster when using a script, but the overall workflow will be completed in less time since the program will complete the processes back to back without needing any user input via the visual interface. 

What language is used in the Global Mapper Script?

Global Mapper Script is a text-based scripting language specific to Global Mapper. With text strings that are easy to understand, Global Mapper Script is an accessible way to automate workflows in the program without needing to learn a larger scripting language. 

For users looking for a more advanced option, Global Mapper Pro does support Python scripting. The integration allows users to automate workflows in Global Mapper and incorporate tools and functionalities from third-party Python libraries. 

May we get a copy of that script to play around with, please?

Below is the Global Mapper Script text shown and used in the webinar. For more information on Global Mapper Script, please visit the scripting section of the program knowledge base.

Keep in mind that this is an example script, and any files/layers named in the script would need to be accessible at the named location on the machine where the script is being run. 

// The file listed here is a CSV of tidal data from NOAA Tides and Currents

DEFINE_VAR_TABLE NAME=”TIDES_TABLE” HAS_COL_NAMES=”YES” \

FILENAME=”C:\Full\Folder\Path\Coastal Analysis GTX\June.csv”

END_VAR_TABLE

VAR_LOOP_START VAR_NAME=”TIDES” VALUE_TABLE=”TIDES_TABLE”

IF COMPARE_STR = “%TIDES:High/Low%=H”

GENERATE_WATER_RISE  \

LAYER_DESC=”Tide %TIDES:Date% %TIDES:Day% %TIDES:Time% at %TIDES:Pred% feet” \

MAX_DEPTH=%TIDES:Pred% ELEVATION_TO_RISE_FROM=”0″ ELEV_UNITS=”FEET”

LOG_MESSAGE “%TIDES:High/Low%, %TIDES:Pred% feet”

ELSE

//Run no model for low tides

END_IF

VAR_LOOP_END

If you are interested in working in Global Mapper, download a 14-day free trial today! Keep an eye out for upcoming GeoTalks Express webinars, and if you have any questions, please contact us.