Mohammed Eltahir's blog

Introduction Inverse distance weighted (IDW) is a type of deterministic method for multivariate interpolation with a known scattered set of points. The assigned values to unknown points are calculated with a weighted average of values available at the known points. The name given to this type of methods was motivated by the weighted average applied, since it resorts to the inverse of the distance to each known point ("amount of proximity") when assigning weights. Practice First, given data were pre-processed and cleaned using Microsoft Excel: Adding data as a vector layer using “add delimited text layer” as follow:  After adding the data, you can save it as a Shapefile for further other processes, and that by “right click” on the layer and select “save as”: Enabling the “interpolation” plugin: Applying “IDW”

Introduction: Digital Elevation Model is basically a three dimensional computer graphic representation of terrain or surface, typically Earth or Moon, March and so on. It used as a precursor of orthophoto and is also used as a base for relief map. It could also be defined as a special case of interpolated, continues surface. The term DEM is used generally to describe the height information without any further consideration of the surface, and usually used as a generic term to describe both Digital surface Model (DTM) and Digital Surface Model (DSM), which sometimes all the three terms are used synonymous. Some of data provider such as USGS define them the same way. Also sometimes, DEM is defined as a subset or the most fundamental component of DTM. Or defining DEM as a rectangular matrices (altitude matrix) and DTM as Triangular Irregular Network (TIN) Type s of DTM or, methods of representing DEM: Mathematically defined surfaces. Raster: altitude matrices. Also known as height map.

Introduction Thissen polygon is a local interpolators that uses nearest neighbours, as they are of high importance ‘first low of geography’. It gives a quick understanding of the space, and starts by defining a search area around the point being process. The space is divided by polygons with each polygon containing one indiviual point. polygons represent that any location inside it, is closer to the point other than any sample point, Also the size of the polygon depend on the point density. Methodology Using QGIS, Thissen polygon (Voronoi) was applied to data of Sudan Admissions and localities that were obtained from (humenreponse.org). North Darfur was the state of application. A comparison between two different ways of splitting the vector was held, and another comparison between the (GRASS and QGIS Geoalgorithms) Voronoi algorithms. Practice Pre-processing: Downloaded the data. Organized on a folder to ease understanding and management. Add data (vector data) to the QGIS environ

WGS 84 is developed by the U.S. Department of Defence, it’s the standard for use in cartography, geodesy, navigation and it’s the most known terrestrial reference system because it’s the reference system for the Global Positioning System (GPS) and that’s the main reason of the high acceptance of the WGS 84 as a primly reference system. Also the U.S. DoD uses it as the standard definition for global reference system for geospatial information. It’s Earth fixed, Earth centred (EFEC) Terrestrial Reference System or a Geocentred datum, based on a set of consistent constant and parameters that describe the Earth’s shape, size, gravity and geomagnetic fields. It’s a global coverage three dimensional Cartesian coordinate system (X,Y,Z), and it’s compatible with the International Terrestrial Reference System (ITRS) also to some extend it can be considered identical to the ITRF. The responsible organization for establishing and maintenance is the National Geospatial-Intelligence Agency (NGI