FAQ

Where in the world can you survey?

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PhotoSat can survey almost everywhere in the world – the high resolution stereo satellites that we use for surveying cover the entire planet, with the exception of small areas at each of the poles.

As PhotoSat can survey anywhere, it is ideal for areas that can’t be accessed on the ground due to safety issues.

See a map highlighting the locations of PhotoSat’s completed satellite surveying projects.

 

How big an area can you survey?

Any size. Story about 10000’s sq km

PhotoSat can survey areas of any size. The largest single project that we have surveyed is 8,000 square kilometers.

The satellites that PhotoSat uses for surveying can acquire satellite data for hundreds of square kilometres in minutes.  We need no on-site presence.

Learn more about PhotoSat’s satellite surveying capabilities.

How do you prove your accuracy?

Accuracy studies and project report

PhotoSat has delivered over 700 satellite surveying projects since 2007.   we have carried out accuracy evaluations on the majority of them. The results of our accuracy studies are consistent with project accuracy evaluations and client feedback.

PhotoSat regularly checks the accuracy of its processing by processing stereo satellite data over two test areas. One test area is west of Asmara, Eritrea where PhotoSat has access to more than 45,000 ground survey points over a 50km by 20km block. The second area is in SE California where PhotoSat uses a very accurate Opentopography.org open source LiDAR survey.

See PhotoSat’s accuracy studies for more information, or check out our blog which has numerous posts detailing PhotoSat’s accuracy and reliability.

Surveying Mine Tailings is difficult because the areas are large and relatively flat, monochrome and frequently change. How does PhotoSat deal with that?

PhotoSat surveys mine tailings storage and disposal areas on many mine sites.  We survey some  mine tailings sites every two weeks.  We routinely produce thickness maps of tailings (isopach maps)  that are accurate to 20cm of thickness variation.

As PhotoSat surveying requires no on-site presence, it is ideal for tailings areas which can often not be safely accessed on the ground.

Learn more about PhotoSat’s mine tailings surveying.

What do you actually deliver

The standard PhotoSat surveying package includes:

 

  • 50cm precision colour or grayscale satellite ortho photo
  • 1m bare earth elevation grid (DEM/DTM) – 15cm, 20cm or 30cm accuracy
  • 50cm or 1m contours (plus 5m, 10m and 50m contours)
  • Colour elevation image (in areas of sparse vegetation)
  • Direction of slope image (in areas of sparse vegetation)

Please see What does PhotoSat deliver to me? for more details.

How does satellite surveying differ from surveying done by a drone?

Drone surveying works best for small areas of up to  a few square kilometers.  Satellite surveying can cover areas of up to hundreds of square kilometres.

The quality of drone surveying can vary, with general accuracy of about 1m in elevation. Very high quality drone surveying can provide accuracy of 5cm in elevation. PhotoSat satellite surveying accuracy ranges from 15cm to 30cm depending on the number of ground control survey points.  

For more information about drone vs. satellite surveying, download PhotoSat’s white paper, Comparison of PhotoSat, LiDAR, Drone and GPS Surveying.

How does satellite surveying differ from surveying done by airborne LiDAR?

Like PhotoSat satellite surveying, airborne LiDAR is able to survey large areas tens or hundreds of square kilometres in size. LiDAR survey can measure the bare ground elevation beneath forest canopy.  LiDAR is the best technology for surveying accurate bare ground elevations with continuous tree cover.  PhotoSat surveying is generally quicker and lower cost than LiDAR surveys.  PhotoSat surveys are often used to update surveys in areas with existing LiDAR surveys.  Areas of ground level changes due to earth moving will be clear of trees and can be accurately surveyed by PhotoSat.

For more information about LiDAR vs. satellite surveying, download PhotoSat’s white paper, Comparison of PhotoSat, LiDAR, Drone and GPS Surveying.

How does satellite surveying differ from surveying done by a GPS ground surveyor?

GPS ground surveying is ideal when surveying up to about 50 ground features, with points easily accessible by road and up to 500m easy walking distance. PhotoSat satellite surveying is able to cover areas of tens or hundreds of square kilometres and requires no ground access or permits This makes it ideal for remote or politically unstable areas.

For more information, see our blog post: Are PhotoSat satellite surveys really more reliable than ground surveys?. PhotoSat also has a white paper available for download which clearly discusses the benefits and drawbacks of the various surveying options.

 

Do you need ground control?

PhotoSat processing with no ground survey points produces 30cm relative and 3m global vertical accuracy. For 30cm absolute vertical accuracy, PhotoSat requires three ground reference survey points per 100km2. Using more ground control survey points can achieve elevation accuracy of 15cm.

 

Please see our blog post to learn more about the effect of different numbers of ground survey points.

How long does it take to get a satellite survey?

New satellite photo collection times differ by geographic location and by season. Once the satellite photos are collected and we receive client ground control, it takes 1 to 3 weeks to deliver 100km2 of surveying.

What format can you deliver in?

Almost any format that you want. We make sure that you can immediately use the data..

  • Contours: 3D ArcGIS Shapefile or 2D MapInfo or 3D DWG
  • Elevation grid: Floating Point Geotiff or .MIG (MapInfo compatible) or ASCII XYZ
  • Colour Image: Geotiff

If you want a different format, just let us know. PhotoSat will deliver any format you prefer – we want to make sure that you can immediately use the data.

See What does PhotoSat Deliver to me? for more information.

How do you get to this level of accuracy ?

PhotoSat uses data processing algorithms, methods and software tools originally developed for the oil and gas seismic processing industry.

To achieve the best possible surveying accuracy, PhotoSat uses sophisticated signal enhancement, noise attenuation and image matching algorithms. Our algorithms run on multi-core GPUs. These accelerate the hundreds of millions of 2D Fourier transforms needed to automatically produce topographic grids. The resulting satellite surveys are usually accurate to better than 20cm elevation.  Accuracy of 15cm can be achieved including several ground survey points in the processing.

PhotoSat has delivered over 700 satellite surveying projects since 2007.  We have carried out accuracy studies on the majority of them.

Learn more about PhotoSat’s process, including the technology used and how the data processing tools are applied.