DEM & Orthophoto Mapping – GIS

A new standard in high quality and precision mapping

iSi provides a variety of satellite-based mapping services. Source files contain the layers needed for GIS applications and can be updated and maintained frequently.

 

DEM Mapping

A DEM (Digital Elevation Model) is used for Orthophoto production and other mapping applications.
Quality DEM products are measured by the precision of the elevation represented by each pixel and how accurately the morphology is captured. High-quality DEM-derived products are measured against several important parameters:

• Terrain roughness
• Sampling density (elevation data collection method)
• Grid resolution or pixel size
• Interpolation algorithm
• Vertical resolution
• Terrain analysis algorithm

 

A Stereo Pair is required for DEM production.

mapping

Prerequisites

Stereo Image

A Stereo Image is necessary to produce a DEM, and therefore must be ordered if a DEM is required.

Grid Spacing

The Customer should specify the Grid Spacing, meaning – the horizontal and vertical distance (in meters) between each pair of coordinates in the grid.

 

If the DEM will be used as a base to an Orthophoto, then the Orthophoto’s scale dictates the recommended Grid Spacing:

 – For a scale of 1:2500 – Spacing of 20m is recommended.

 – For a scale of 1:5000 – Spacing of 40m or lower is recommended.

 – For a scale of 1:10,000 – Spacing of 50m or lower is recommended.

GCPs (Ground Control Points)

 GCPs are optional but required to achieve better accuracy: With well distributed GCPs (8-9 points), horizontal accuracy of 5m can be achieved. GCPs are supplied by the customer.

 

Orthophoto Mapping

An Ortho-rectified satellite Image, used for mapping applications

 

An Orthophoto Product is produced from satellite image and a DEM. The DEM used is obtained in one of three ways;
• Produced by iSi (DEM required)
• Supplied by the customer
• iSi can use an existing Free-for-Commercial-Use DEM – the SRTM, which has a grid spacing of 90m.

mapping-2

Prerequisites

Basic/Stereo Image

Stereo Image.

DEM

One of 3 options: – Produced by iSi (DEM required) – Supplied by the customer – iSi can use an existing Free-for-Commercial-Use DEM – the SRTM, which has a grid spacing of 90m or the ASTER GDEM which has a grid spacing of 30m.

Product Scale

 The Customer should specify the final product’s scale. Minimal: 1:2500.

 

 

 

 

 

 

 

 

 

Mosaic

Comprised of several Orthophoto Products together, for mapping applications

mapping-3

 

 

Prerequisites

 

Image

Stereo Image.

DEM

One of 3 options: – Produced by iSi (DEM required) – Supplied by the customer – iSi can use an existing Free-for-Commercial-Use DEM – the SRTM, which has a grid spacing of 90m or the ASTER GDEM which has a grid spacing of 30m.

Product Scale

The Customer should specify the final product’s scale. Minimal: 1:2500.

 

 

 

 

 

 

 

© 2016 ISI All rights reserved