GIS related | rednex4x4

Category: GIS related

asterray- hetay theroay gis ataday

Filed under: assignments, GIS related — Leave a comment

March 8, 2011

1.is an angular measurement in a spherical coordinate system. The vector from an observer to a point of interest is projected perpendicularly onto a reference plane; the angle between the projected vector and the reference vector on the reference plane is called the azimuth.

2.Euclid was a greek mathemetician, Also called the father of geometry ,Euclidian distance is the ordinary distance between two points.

3.Pythagorean theorem is a mathematics related to Eucludian geometry among the three sides of a right triangle, In any right triangle, the area of the square whose side is the hypotenuse (the side opposite the right angle) is equal to the sum of the areas of the squares whose sides are the two sides that meet at a right angle. The equation is a2xb2=c2 which is often called the pythagorena equation.

4.Map algebra is a simple and an elegant set based algebra for manipulating geographic data, in arc gis map algebra is used to preform operations using objects,actions and qualifiers.

5.The 7 key functions of a spatial analysist consist of,

Derive new information from existing data
Apply Spatial Analyst tools to create useful information—for example, derive distance from points, polylines, or polygons; calculate population density from measured quantities at certain points; reclassify existing data into suitability classes; or create slope, aspect, or hillshade outputs from elevation data.

Find suitable locations
Find areas that are the most suitable for particular objectives (for example, siting a new building, or analyzing high risk areas for flooding or landslides) by combining layers of information. Based on a set of input criteria (for example, where areas of vacant land with the least steep terrain that are nearest to roads would be most suitable), areas in green in the graphic below are the most suitable locations for building; areas in red are least suitable. Areas in yellow are of medium suitability.

Identify the best path between locations
Identify the best path or optimum corridors for roads, pipelines or animal migration. Factor in economic, environmental, and other criteria.

Perform distance and cost-of-travel analyses
Create Euclidean distance surfaces to understand the straight-line distance from one location to another, or create cost-weighted distance surfaces to understand the cost of getting from one location to another based on a set of input criteria you specify

Perform statistical analysis based on the local environment, small neighborhoods, or predetermined zones
Perform calculations on a per-cell basis between multiple rasters, such as calculating the mean crop yield over a 10-year period. Study the neighborhood by calculating, for example, the variety of species in a neighborhood. Determine the mean value in each zone, such as the mean elevation per forest zone.

Interpolate data values for a study area based on samples
Measure phenomenon at strategically dispersed sample locations, and predict values for all other locations by interpolating data values. For instance, create raster surfaces from elevation, pollution or noise sample points.

Clean up a variety of data for further analysis or display
Clean up raster datasets that contain data that is erroneous or irrelevant to the analysis at hand or is more detailed than you need.

Comment

Defenitons

Filed under: assignments, GIS related — Leave a comment

1. TIN-(Triangulated Irregular Network) A vector-based data structure for storing terrain information in digital terrain modeling, it is a surface representation derived from irregularly spaced points and breakline features. Each sample point has an x, y coordinate and a z value or surface value.

2. Interpolated values-interpolation is a method of constructing new data points within the range of a discrete set of known data points, the interpolated values can be represented by color or number etc.
3. Mass points-An irregularly distributed sample point, with an x-, y-, and z-value, used to build a triangulated irregular network(TIN). Ideally, mass points are chosen to capture the more important variations in the shape of the surface being modeled.

4. DEM-(data elevation model)-a DEM file is a simple, regularly spaced grid of elevation points .A DEM can be represented as a raster (a grid of squares, also known as a heightmap when representing elevation) or as a triangular irregular network (TIN). The TIN DEM dataset is also referred as a primary (measured) DEM, whereas the Raster DEM is referred as a secondary (computed) DEM

5. Contiguous data-Data that are stored in a collection of adjacent locations in a computer memory device,
contiguous data is data that is moved or stored in a solid uninterrupted block. In general, contiguous data can be accessed more quickly than data that is stored in fragments because fewer access operations will be required. Files are sometimes stored in fragments so that storage space can be used more efficiently (all the small spaces can be used).

6. Re-sampling-can refer to re sizing of images or data sources it can also be a filter to the data and changes the sampling rate of the signal by decimation or interpolation.

7. Raster- Raster data is a grid of cells covering an area of interest. Each pixel, the smallest unit of information in the grid, displays a unique attribute.An example of raster data is a scanned image or photograph. A line drawn in a raster format must be defined by a group of pixels along the length of the line. As a result the size of a raster file is larger than that required by a vector file.

8. Cell-is a three-dimensional polyhedron element that is part of the boundary of a higher-dimensional polytope

9. Zone-a zone is an area of set perametres that has information inside of the certain area
for example pg is in utm zone 10, a specific area that has been divided out of the bc zones.

10. Grid-can be used to define locations on maps using Cartesian coordinates. Grid lines on maps define the coordinate system, and are numbered to provide a unique reference to features.
for example x,3 y,7