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Calculate Slope for a Site Suitability Model

I recently received a call from one of our Surfer users who was trying to create a site suitability model for a new manufacturing development. The user needed to find areas within the proposed site where the slope was under 10 degrees. The site suitability model required specific slope to be respected; the areas that were under the threshold criteria of 10% would be considered potential locations within the site to locate the new development.


A site suitability model can be easily developed in Surfer by creating a slope grid from a digital elevation model or DEM for the area, masking the slope grid to the site boundary, and creating a contour map that highlights the areas that meet the 10% or under criteria. Since this is such an interesting workflow, I thought it would be a great topic to blog about it so others in the Surfer community could benefit from seeing the approach.


Create a Slope Grid in Surfer
The first step in creating the suitability model is to determine the slope of the DEM of the site using Surfer. Surfer’s Grid | Calculus command can be used to do this easily by following these steps:

  1. In Surfer, click Grid | Calculus.
  2. In the Open Grid dialog, navigate to the GRD or DEM and click Open.
  3. In the Grid Calculus dialog, expand the Terrain Modeling selection and select Terrain Slope.
  4. Name the Output Grid File and click OK to create the slope grid.

Highlighting the 10% Slope Areas
Now that the slope grid has been created from the digital elevation model, it needs to be blanked by the proposed site boundary so that only the areas within the site boundary contain slope data. To blank the slope grid:

  1. Click Grid | Blank.
  2. In the Open Grid dialog, navigate to the digital elevation model and click Open.
  3. In the Open dialog, navigate to the BLN file of the area of interest and click Open.
  4. In the Save Grid As dialog, name the grid and click Save.


Now that the slope grid has been blanked to the potential site boundary, a contour map can be created that highlights the areas within the site boundary that have a slope of 10% or less. This can be done by adding slope contours at 0% slope, 5% slope, and 10% slope.

  1. Click Map | New | Contour Map.
  2. In the Open Grid dialog, navigate to the blanked slope grid and click Open.
  3. In the Object Manager, click the Contours layer to select it.
  4. In the Property Manager, click the Levels tab.
  5. Change the Level Method to Advanced and click the Edit Levels button.
  6. In the Levels for Map dialog, delete all of the levels except 0, 5, and 10.
  7. Assign these levels an appropriate color and fill pattern and click OK.

 


We now have a map of the locations within the site boundary that are less than 10% slope. In the map above, areas that are green are the most suitable for locating the new development and are under 5% slope. Areas that are highlighted in yellow are between 5% and 10% slope, which is still suitable for locating the development.  All areas in red have a slope over 10% and are not good location candidates for the new development. The contours can also be exported from Surfer to be used in 3rd party mapping and CAD applications.

 

 

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01 December 2015
Surfer
Real Life Applications

We recently received an update on the case of the missing diver. The blog has been rewritten to reflect this new information.

November 20, 2011 - Four recreational divers went looking for wreckages at the bottom of De Nieuwe Meer in Amsterdam, Netherlands, an approximately 30 meter deep lake. The group split into two pairs and set out on their adventure. They were well-equipped and all wore full face diving masks.

Around 11:30 AM, an emergency call was made by the diving group to report a fellow diver was missing. The woman diver, who was paired up with the missing 55 year old man from Amstelveen, reported looking back for him, but all she could see was a cloud of sediment. The two had just climbed over a 6 foot cooling water pipe. They were aware of the pipe, which was used to suck up water from the lake to cool several city buildings, as they had crossed it during previous dives. Her diving partner never surfaced.

Following the call, emergency responders arrived on scene including three different fire departments, the police, and ambulance service. The fire department immediately deployed divers and boats to locate the missing diver. Thereafter, the police deployed cadaver dogs who were trained to locate people beneath bodies of water.

Rescuers
Rescuers operating the sidescan SONAR. Picture from AT5.

According to Dutch protocol, the first hour a diver is missing, the "Golden Hour," is the most critical as chances are greater that the person will be found alive. Thereafter, chances of a lifesaving operation diminish. For this search and rescue, the Golden Hour was extended because the diver was wearing a full face diving mask, and his oxygen tank had approximately 3 hours of dive time. Even if the diver was found unconscious, the full face mask should prevent water from entering the lungs and should keep the oxygen flowing.

Due to dense fog, the search was called off on the first day; however, the other two male divers who were part of the original group, continued to search for their missing friend, but to no avail. The following day, National Police divers and specially trained cadaver dogs joined the search. Due to the cold water temperatures and the length of time the diver was underwater, it was unlikely he would be found alive. Another special police task force joined the retrieval mission and came prepared with side scan sonar to collect data of the lake bottom. On the third, fourth and fifth days of the search, the Royal Dutch Navy brought in autonomous underwater vehicles (AUVs) but, even after these efforts, was unable to locate the body.

On November 25th, the site was opened to any public entity wishing to participate in the search. It was at this point when Henk de Vries and the former Metaldec Survey BV entered the picture. Metaldec Survey used Golden Software products Didger, Voxler, and Surfer for a wide variety of projects including visualization work for several police departments. They had previously helped the police and fire departments to set protocols for forensic drowning scenes and were often known to volunteer their efforts for various police projects.

At the request of private police agents, Mr. de Vries and his team got to work. The original diving group had been equipped with devices that took depth recordings every 30 seconds during their dive. Mr. de Vries used this data, along with echo sounding data, and created a 2D contour map and 3D depth map of the lake with the help of Didger and Surfer. These maps were used to identify the dive path taken by the missing man to determine approximate location where the diver had gone missing.

Thereafter, a higher resolution bathymetric map was created by the Metaldec Survey team. In this refined area, Metaldec set up their side scan and Echo sounder sonar equipment to collect further data. The side scan and bathymetric map played a crucial role in the search endeavours as SAR divers could “see” the lake’s bottom. They were then able to safely plan their dive by using the given depths as detailed on the bathymetry map and address any dangers such as barbed wire, cables, or fishing nets prior to the dive. All dives that utilize a bathymetry map prior to the dive can save lives as it reduces the chance of decompression sickness, also known as the bends, since divers can avoid unexpected and drastic dive ascents and descents and can also calculate the maximum bottom time.

 

Additionally, the Sonar Tow-Fish, an expensive tool used to collect sonar data, needed the bathymetric information so it could be towed 20 feet above the bottom of the lake. Without the bathymetric map, it would have been almost impossible to coordinate when the Tow-Fish should be raised or lowered depending on the lake bottom.

b2ap3_thumbnail_3D-Example-of-Nieuwe-Meer-drowning-map.png

3D Surface Map of De Nieuwe Meer created with Surfer

Mr. de Vries overlaid his sonar and bathymetry data on a Google Earth image of the lake and made a surprising, and concerning, discovery. The pipeline running through the middle of the lake did not cross the entire lake as everyone had assumed. Instead, it stopped at an inlet near the center of the lake. No previous divers had ever mentioned this, but it was assumed all SAR divers could be in danger of being sucked into the pipe. All diving was immediately halted.

b2ap3_thumbnail_Missing-Diver-Sonar-Images.png

Sonar images overlain on Google Earth image of De Nieuwe Meer

Interestingly, this inlet area was near a location where the SAR dogs were alarmed and where the original diving group believed their fellow diver disappeared. It was initially thought the man was sucked into the 6 foot wide pipe inlet. After further analysis of the sonar images and discussions with the pipe owner, it became clear the inlet was closed off by a wire cap. The inlet actually consisted of 6 upright pipes that were capped with wire meshes to prevent debris from clogging the pipe. It was then assumed the diver became stuck on the pipe or on one of the wire caps.

The lake was dredged to no avail. On January 6, 2012 the search was called off permanently, as no body had been found.

A year and a half later, on July 6, 2013, a local cadaver dog foundation searched again around the pipe inlet. As before, the dogs became alarmed in this vicinity. A drop camera (video camera connected to a monitor on a boat) was lowered, and an image that appeared to be a human face was spotted. The following week, the Mayor of Amstelveen saw the video images and asked the Dutch Royal Navy to revisit the site and inspect the new findings.

A few days later the Navy arrived on the scene and searched again with their AUV sonar. As before, the bathymetric Surfer map and side scan sonar mosaic helped the Navy program their AUV and prepare individuals for another dive. The AUV data didn’t initially show the body, but later that day, the missing diver was found by the Navy and his body was successfully recovered.

An autopsy was unable to reveal the cause of death. Instead, the man’s dive computer, used to track his diving depth intervals, was used to piece together the final minutes of his life. The data showed the man had ascended to the surface of the lake then descended back to the bottom. Five minutes after he went missing, his computer showed no movement of any kind. The man most likely died of heart failure or a stroke. This hypothesis was supported by the fact his oxygen tank was half-full and his diving gear was completely intact.

The case of the missing diver became one of the largest missing person cases in Holland. Thanks to the Royal Navy, police and fire departments, detective agencies, and many volunteer groups and individuals, the diver was finally laid to rest.

Henk De Vries now works for RemoSens BV (short for remote sensing) where he and his team continue to utilize Golden Software products to create a wide variety of maps and models.

www.remosens.nl

To read more about this case, check out the featured article in GeoConnexion International Magazine: http://www.geoconnexion.com/uploads/publication_pdfs/int_v15i14-030-Gold16211EB.pdf

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25 January 2016
Surfer

Quite often people will ask, “What are the differences between Surfer and QGIS?” Below is a comparison of the main features and functionality of each program. Surfer, as you may know, provides 2D and 3D contouring complete with surface mapping software. QGIS has an assortment of plugins, and we haven’t been able to review them all. I encourage you review and let me know if there is any missing information. As new information comes in, I’ll be sure to update the matrix below.

  Surfer version 13 QGIS version 2.12.3
Price 1-3 licenses $849/license
4-10 licenses $805/license
11+ licenses $765/license
Free
Development Model Commercial Open source
Plug-ins
Red X
Green Check
Free Resources
Website
Green Check
Green Check
Live technical support
Phones
Green Check
Red X
Email
Green Check
Red X
Live chat
Green Check
Red X
Knowledge Base
Green Check
Red X
Forums
Green Check
Green Check
User Groups
Red X
Green Check
Documentation
In-program help
Green Check
Red X
Training manual
Green Check
Green Check
Paid for Resources
Full PDF user guide
Green Check
Red X
Live training
Green Check
Provided by
Golden Software &
authorized resellers
Green Check
Provided by 3rd party
contributors
Map Types
Base map
Green Check
Green Check
Contour map
Green Check
Green Check
Image map
Green Check
Green Check
Post map
Green Check
Green Check
Classed post map
Green Check
Red X
Shaded relief map
Green Check
Green Check
Vector map (1-grid)
Green Check
Red X
Vector map (2-grid)
Green Check
Red X
Watershed map
Green Check
Green Check
Viewshed map
Green Check
Green Check
3D surface map
Green Check
Green Check
3D wireframe map
Green Check
Red X
Pie chart thematic map
Red X
Green Check
Histogram thematic map
Red X
Green Check
Map Features
Axes
Green Check
Red X
Profiles
Green Check
Green Check
Scale bar
Green Check
Green Check
Color scale
Green Check
Green Check
Coordinate systems
Green Check
Green Check
Import/edit/export attributes
Green Check
Green Check
Measure distance
Green Check
Green Check
Measure angles
Red X
Green Check
Digitize XYZ points
Green Check
Green Check
Overlay maps
Green Check
Green Check
Stack maps
Green Check
Red X
Log contours
Green Check
Red X
Save/load contour levels
Green Check
Red X
Edit contours
Red X
Green Check
Inline contour labels
Green Check
Green Check
Map transparency
Green Check
Green Check
Gridding/Interpolation/Rasterizing
Inverse distance
Green Check
Green Check
Kriging
Green Check
Red X
Minimum curvature
Green Check
Red X
Modified Shepard's method
Green Check
Red X
Natural neighbor
Green Check
Red X
Nearest neighbor
Green Check
Green Check
Polynomial regression
Green Check
Red X
Radial basis function
Green Check
Red X
Triangulation with linear interpolation
Green Check
Green Check
Moving average
Green Check
Green Check
Data metrics
Green Check
Green Check
Local polynomial
Green Check
Red X
Function grid
Green Check
Red X
Variogram modeling
Green Check
Red X
Grid date/time data
Green Check
Red X
Grid reports with statistics
Green Check
Red X
Faults
Green Check
Green Check
Breaklines
Green Check
Green Check
Anisotropy
Green Check
Red X
TIN support
Red X
Green Check
Grid Functions
Math
Green Check
Green Check
Calculus
Green Check
Green Check
Filter
Green Check
Green Check
Spline smooth
Green Check
Red X
Blank/null
Green Check
Green Check
Convert
Green Check
Green Check
Extract
Green Check
Green Check
Transform
Green Check
Red X
Mosaic
Green Check
Green Check
Volume
Green Check
Green Check
Slice
Green Check
Red X
Residuals
Green Check
Red X
Grid info
Green Check
Green Check
Grid node editor
Green Check
Red X
Assign coordinate system
Green Check
Green Check
Regrid
Red X
Green Check
Grid metadata
Red X
Green Check
Grid transpose
Green Check
Red X
3D File Viewer
Red X
Green Check
Worksheet
Green Check
Red X
Automation
Green Check
Green Check
Import/Export
Import options
33
22
Export options
27
28
Open grid
47
64
Save grid
24
64

Beyond the actual functionality, another difference between Surfer and QGIS is the development models. Surfer is a commercially developed program whereas QGIS is open source and is developed by a community of contributors. While it’s difficult to quantify, I believe it’s worth mentioning the pros and cons, according to me, associated with our commercial software model and QGIS’s open source model.

As a commercially developed product, Surfer comes with a price tag. Since people are spending their hard earned dollars, it is our duty to develop a high quality product. Our developers adhere to rigorous developmental principles, all code is reviewed by another developer, and Surfer undergoes extensive internal and external testing periods. We put a great focus on the usability of Surfer to ensure feature are easy to access. Beyond the quality of the product, we take great pride in the support we provide Surfer customers. All technical support is free for any version of the product (yes, even back to MS-DOS). This includes live phone, email, and chat along with our 24x7 web resources including the open forums and knowledge base. We also have a dedicated documentation writer who ensures all aspects of Surfer is documented.

Another point worth mentioning is longevity. Golden Software has been around since 1983, and we’ve sold licenses in 185 countries and on all seven continents.

Alternatively, as an open source product, QGIS is completely free and is developed through the good intentions of anyone wishing to contribute to its feature set. As such, anyone from a hobby developer to a senior developer can contribute, but there are minimal quality controls around code quality and program usability. QGIS does seem to have a strong community of followers which is important because it is to this community you will turn for technical support. Paid-for commercial support is also offered through 3rd party contractors. Like the development of QGIS, documentation is handled through the good intentions of volunteers which results in a wide range of poorly documented features to well documented features.

Let me know your thoughts on Surfer vs. QGIS. What do you like and what do you dislike about each program?

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01 November 2016
Surfer
Real Life Applications

Golden Software’s Surfer program can be used in so many applied-science industries for so many different uses, I sometimes forget that it is equally applicable to more business or art-oriented fields. I had a user contact me recently with the following request (paraphrased):

“I have a paper copy of the blueprint of a house, and on it I’ve written elevation measurements that I collected while surveying on the premises. I also have a DXF file of the floorplan of the house. How can I create elevation contours in Surfer and limit them to the shape of the house?”

What a neat application! From a piece of paper and one digital file, can Surfer generate a beautiful and informative contour map of elevation values? You bet it can!

There are a few steps to this process. You need to convert your paper data into digital x,y,z data, grid that x,y,z data, create a BLN file of the outline of the house, and blank the grid file with that outline. Then you can create a contour map of the blanked grid, and display the DXF of the floorplan overlaid on the contours if desired. The steps for each of these processes are detailed below, and sample files are attached so you can step through this process yourself.

  1. Import the DXF as a base layer:
    1. Click Map | New | Base Map.
    2. In the Import dialog, select floorplan.dxf (vectorized using Surfer’s Draw menu commands from a JPG I found here) and click Open.
    3. In the DXF Import Options dialog, leave the defaults and click OK.
    4. Click on the Map in the Object Manager.
    5. On the Limits page in the Property Manager, make note of the xMin, xMax, yMin, and yMax.

spatialextents.png

    1. Uncheck all four axes in the Object Manager.

floorplan1.png

  1. Draw the boundary and export to BLN:
    1. Click Draw | Polygon.
    2. Click around the outside of your floorplan, holding the CTRL key while you click to snap the line to perfectly horizontal, perfectly vertical, or at a perfect 45 degree angle.
    3. Double click on the last point to finalize the polygon and then press ESC to exit drawing mode.

floorplan_outline.png

    1. Uncheck the box next to the Base-floorplan.dxf layer in the Object Manager.
    2. Click File | Export.
    3. In the Export dialog, set the Save as type to BLN Golden Software Blanking (*.bln), give your file a name (like Blanking) and click Save.
    4. On the Scaling page in the Export Options dialog, change the Scaling source to Map: Base-floorplan.dxf.
    5. On the BLN Options page, in the Blank areas section, toggle Outside.
    6. Click OK to export the BLN file.
    7. If desired, uncheck or delete the Polygon from the Object Manager.
  1. Digitize the data:
    1. Click File | Import.
    2. Select the PaperNotes.pdf file (a ‘scan’ of the paper notes you made in the field) and click Open.
    3. Right click on the Image in the Object Manager and click Order Objects | Move to Back.
    4. Check the box next to the Base-floorplan.dxf layer in the Object Manager.
    5. Click and drag the handles on the image until the image lines up with the DXF.
    6. Select the Base-floorplan.dxf layer.
    7. Click Map | Digitize.
    8. Click on the first point on the map where you have recorded an elevation value.
    9. In the Digitized Coordinates dialog, type a comma and a space after the second value in row 1 and then type your elevation value. In this example, the elevation value is displayed in red text next to the point on the image.

floorplan_digitize.png

    1. Click to the next empty row (2 this time).
    2. Repeat steps 3h through 3j for the other elevation values you have recorded.
    3. In the Digitized Coordinates dialog, click File | Save As.
    4. In the Save As dialog, change the Save as type to Data Files (*.dat), give your file a name (like Elevation), and click Save.
    5. Click X in the upper right corner of the Digitized Coordinates dialog to close it, and press ESC to exit digitizing mode.
    6. If desired, you can now delete or turn off the Image.
  1. Grid the digitized DAT:
    1. Click Grid | Data.
    2. In the Open Data dialog, select your Elevation.dat file and click Open.
    3. In the Grid Data dialog,
      1. Make sure the X, Y, and Z Data Columns are set to Columns A, B, and C from your digitized DAT file.
      2. Set your Gridding method (I’ll leave the default, Kriging).
      3. Make sure the Maximum in both the X Direction and Y Direction of the Grid Line Geometry section is larger than the maximums you made note of in 1e, and verify that the Minimums are less than the minimums you made note of. Since our minimums are in the low single digits and the maximums are around 850, using 0 for the minimums and 900 for the maximums here is just fine.
      4. If desired, increase the # of Nodes or decrease the Spacing to get a higher-resolution grid file (I will decrease the Spacing to 3 in both directions).
      5. Click OK.

griddata.png

    1. Click OK in the dialog telling you the grid file was created.
  1. Blank the grid file:
    1. Click Grid | Blank.
    2. In the Open Grid dialog, choose your Elevation.grd file and click Open.
    3. In the Open dialog, choose your Blanking.bln file and click Open.
    4. In the Save Grid As dialog, give your output file a name (like Elevation_blanked.grd) and click Save.
    5. Click OK in the dialog telling you the grid file was blanked.
  2. Plot your contour map:
    1. Select your base map.
    2. Click Map | Add | Contour Layer.
    3. In the Open Grid dialog, select your Elevation_blanked.grd file and click Open.
    4. If prompted to expand the map limits, click No.

Now that your contour map is created, you can fill it as desired, and rearrange the layer ordering so the details in your floorplan display over top of the contours.

floorplan_final.png

It’s amazing how much you can do from so little. From one piece of paper with some elevation values jotted down, you can create a stunning and informative image like this one!

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