X

NV5 Geospatial Blog

Each month, NV5 Geospatial posts new blog content across a variety of categories. Browse our latest posts below to learn about important geospatial information or use the search bar to find a specific topic or author. Stay informed of the latest blog posts, events, and technologies by joining our email list!



Thermal Infrared Echoes: Illuminating the Last Gasp of a Dying Star

Thermal Infrared Echoes: Illuminating the Last Gasp of a Dying Star

4/24/2025

This blog was written by Eli Dwek, Emeritus, NASA Goddard Space flight Center, Greenbelt, MD and Research Fellow, Center for Astrophysics, Harvard & Smithsonian, Cambridge, MA. It is the fifth blog in a series showcasing our IDL® Fellows program which supports passionate retired IDL users who may need support to continue their work... Read More >

A New Era of Hyperspectral Imaging with ENVI® and Wyvern’s Open Data Program

A New Era of Hyperspectral Imaging with ENVI® and Wyvern’s Open Data Program

2/25/2025

This blog was written in collaboration with Adam O’Connor from Wyvern.   As hyperspectral imaging (HSI) continues to grow in importance, access to high-quality satellite data is key to unlocking new insights in environmental monitoring, agriculture, forestry, mining, security, energy infrastructure management, and more.... Read More >

Ensure Mission Success With the Deployable Tactical Analytics Kit (DTAK)

Ensure Mission Success With the Deployable Tactical Analytics Kit (DTAK)

2/11/2025

In today’s fast-evolving world, operational success hinges on real-time geospatial intelligence and data-driven decisions. Whether it’s responding to natural disasters, securing borders, or executing military operations, having the right tools to integrate and analyze data can mean the difference between success and failure.... Read More >

How the COVID-19 Lockdown Improved Air Quality in Ecuador: A Deep Dive Using Satellite Data and ENVI® Software

How the COVID-19 Lockdown Improved Air Quality in Ecuador: A Deep Dive Using Satellite Data and ENVI® Software

1/21/2025

The COVID-19 pandemic drastically altered daily life, leading to unexpected environmental changes, particularly in air quality. Ecuador, like many other countries, experienced significant shifts in pollutant concentrations due to lockdown measures. In collaboration with Geospace Solutions and Universidad de las Fuerzas Armadas ESPE,... Read More >

Rapid Wildfire Mapping in Los Angeles County

Rapid Wildfire Mapping in Los Angeles County

1/14/2025

On January 8, WorldView-3 shortwave infrared (SWIR) imagery captured the ongoing devastation of the wildfires in Los Angeles County. The data revealed the extent of the burned areas at the time of the capture, offering critical insights for rapid response and recovery. To analyze the affected region, we utilized a random forest... Read More >

1345678910Last
«May 2025»
SunMonTueWedThuFriSat
27282930123
45678910
11121314151617
18192021222324
25262728293031
1234567
16816 Rate this article:
2.0

Dimensional Analysis, Unit Conversions, and Physical Constants

Anonym

Physical Constants

When I was in college, I memorized most of the common physical constants, such as Plank's Constant or Earth's mass. To be honest, today I don't remember most of these without looking them up. Although this isn't too difficult to do in the era of the internet where I can copy and paste the search result of "Plank's Constant" from my browser into the IDL editor, IDL makes it much easier by storing many of these physical constants in the !CONST system variable. For example, if I am writing code that calculates gravitational forces using the Gravitation Constant, I can simply use !CONST.G. More convenient than just saving me a few seconds of typing a long number as a variable, however, is the fact that IDL automatically stores these values as double precision, ensuring maximum accuracy each time they are used.

Unit Conversion in IDL

Another helpful tool when developing code that involves processing dimensional data is IDLUNIT, which can perform unit conversion, calculate simple mathematical expressions, and much more. Similar to !CONST, all values and calculations are kept in double precision for maximum accuracy.

Here is an example of how you may convert PSI to Pascals:

PsiToPa = (IDLUnit('psi -> Pa')).Quantity

PaValue = psiValue * psiToPa

IDLUNIT even allows a user to add custom units, which is helpful when using non-standard units. For example, how many Olympic sized swimming pools does it take to fill Sydney Harbour? Let's define a unit of 'pool' as 50 x 25 x 2 meters = 2500 m3, and let's define Sydney Harbour as 494 Gigaliters (source: Wikipedia: List of unusual units of measurement).

IDLUnit.AddUnit, 'pool', '2500 m^3', PLURAL='pools'

IDLUnit.AddUnit, 'Sydharb', '494 Gl', PLURAL='Sydharbs'

IDLUnit('1 Sydharb -> pools')

IDL tells us that 197,600 pools could fill Sydney Harbour.

IDL's help page for the IDLUNIT topic contains many additional examples.

Unit Converter Widget

In addition to performing unit conversions in code or at the command line, IDL has an interactive unit converter. To launch this converter, run 'idl_convert' or select 'IDL Converter' from the IDL Workbench's Macros menu. Notice that the custom units defined in the example above are included in this tool.

 

Please login or register to post comments.