• Bogdan-Vasile Ileanu added an answer:
    What is the minimum acceptable sample size in AHP when you have 13 variables under consideration?
    I have a range of experts but I am not sure how many questionnaires I should run.
    Bogdan-Vasile Ileanu

    now i found some suggestion : Kardi Teknomo

  • Tayyab I Shah added an answer:
    Why there is a shift between georeferenced SOI toposheet and Google Earth images?

    Why there is a shift between referenced toposheet and google earth images.

    What may be reasons other than projections and scale.

    Is there a shift in the positions when taking historical images wrt to acquisition dates. What are the reasons for it.

    Tayyab I Shah

    Hi Vinod - i think you are using a scanned copy of SOI sheets.....if that's correct then its not easy to remove that shift...Goodluck

  • Hein Van Gils added an answer:
    Is the FAO Forest Resources Assessment in your country using satellite Remote Sensing?

    To my surprise many countries appear to report to the FAO every 5-years on forest extent statistics without using satellite Remote Sensing. I would appreciate to learn about countries that do use RS in their FRA. And for those countries that do not, about their motivation.

    For an example of uncertainties in FRA forest extent statistics, please refer to my profile.

    Hein Van Gils

    Somehow deforestation and spontaneous reforestation (attached Majella paper) rates at landscape level show a rather narrow range. Any idea why?

    My experience on forest extent data provided by forest district officers is that these represent forest land (forest use; forest reserves) rather than forest cover (attached Rwanda paper). Also data from Indonesia often refer to forest land rather than forest cover in my experience. No problem, unless you compare between countries and over time within countries.   

    • Source
      [Show abstract] [Hide abstract]
      ABSTRACT: Question: Can the pattern and pace of spontaneous Fagus forest expansion from 1975 to 2003 be accurately detected with mid-resolution satellite imagery? Can the historical Fagus expansion be modelled on the basis of environmental predictors? If so, where are the highest probabilities for future Fagus expansion? What are the implications for park management? Location: Majella National Park, Italy, > 1000 m a.s.l.; municipalities of S. Eufemia and Pacentro. Methods: Fagus cover change was detected by overlaying three classified sequential satellite images. Historical Fagus expansion was related to environmental variables using ordinary logistic and autologistic regression models. Fagus expansion probabilities were generated with the best predictive model. Results: From 1975 to 2003 Fagus advanced into abandoned farmland and subalpine pastures from the contiguous, midaltitudinal Fagus forest and from Fagus outliers, at a rate of 1.2 % per year. Substantial spatial and temporal variations in expansion rates were detected. The ordinary and autologistic models based on the single predictor Distance-from-Fagus-1975 forecasted the Fagus expansion well (AUC 0.81 resp. 0.88). Multiple logistic models, including the topo-climatic and substrate predictors, improved prediction insignificantly. The strong predictive power of proximity to historical Fagus presence is explained by the dispersal biology of Fagus combined with the shading impact of the Fagus canopy at the forest fringe. Conclusion: Decade-long Fagus expansion patterns might be reliably forecasted by proximity to historical Fagus distribution. Consequences for park management options are outlined.
      Applied Vegetation Science 12/2008; 11(4):539-546. DOI:10.3170/2008-7-18568

    + 1 more attachment

  • Gamal Seedahmed added an answer:
    Besides LiDAR, through which other means can you generate powerful point cloud data nowadays?
    Feature extraction
    Gamal Seedahmed

    Dear Nashon,

    As  Geoffrey  said use photogrammetry for the generation of 3D point cloud. Please check the attached file for 3D modeling. it is a  part of a final year project in surveying engineering for one of my student. The title of the project is: 3D mapping for small areas using close range photogrammetry.



  • Abdel Rahim Ruby Abdel hamid Hassanain added an answer:
    Are there any programs to convert observed gravity into normal gravity value on the surface of the ellipsoid (WGS84) and free air anomaly?

    I am looking for a program to compute into Theoretical (Normal) Gravity (γ) value on the surface of the ellipsoid (WGS84) and Free-Air Anomaly (Δgf) with knowing Observed (or measured) Gravity (g) on the earth surface

    Abdel Rahim Ruby Abdel hamid Hassanain

    Hi, all

     i have excel program sheet based on Gravity definitions & anomaly computations (NGA document)

    Download  file :- Gravity definitions & anomaly computations (NGA document)

    and the latest version of World Geodetic System (WGS) 1984

    see attached for excel sheet

    Please testing the excel program sheet... when there are errors Contact with me

    Abdel Rahim

  • Abdel Rahim Ruby Abdel hamid Hassanain added an answer:
    What is the difference between EMPCOV and COVFIT ?

    in the program GRAVSOFT , two Sub programmes

    - Python Interface to “EMPCOV” (Program empirical covariance functions)

    - Python Interface to “COVFIT” (Fit empirical functions to analytic models)

    in figure below , what is empirical covariance functions and analytical covariance functions

    I know how to be compute empirical covariance, but How can be obtained analytical covariance functions

    + 1 more attachment

    Abdel Rahim Ruby Abdel hamid Hassanain

    Dear Ramouz

    Thank you  for adding your answer ...

    Now  I know use "EMPCOV and COVFIT"

    Very Thank

    Abdel Rahim

  • Abdel Rahim Ruby Abdel hamid Hassanain added an answer:
    How to use spherical harmonic expansions for Earth's topography to extract (DTM’s)?

    HI, all

    I want to get the program to extract Digital terrain models (DTM’s) or

    Digital height models (DHM’s) for a certain area from Global Gravity Field Models related to Topography For example  dV_ELL_RET2012

    Abdel Rahim Ruby Abdel hamid Hassanain

    Dear Dr. Vagner

    yes , I  would like to compute the residual terrain modelling quantities (residual height anomalies, gravity anomalies,) 

    I am waiting for sending program (a MatLab script) to do that
    Thank you very much
    Abdel Rahim

  • Abdel Rahim Ruby Abdel hamid Hassanain added an answer:
    How development Global Gravity Field Models like EGM96?

    I have some questions about Global Gravity Field Models (ICGFM).
    Where How to Calculate Coefficients of this model? I.e. I need the program to compute spherical harmonic analysis of EGM model.

    Abdel Rahim Ruby Abdel hamid Hassanain

    Dear Eng, Ahmed

    Thanks for adding your answer

    this paper Failure during download

    It can be sent to email (

    Abdel Rahim

  • Liu Qiang added an answer:
    How to calculate the length of the long migration route?

    I just get a migration route from south China to Russia. Firstly, I  calculate  the length using arcgis with wgs1984 web mecator coordinate systerm. The length is 5800 km. Then I checked the route in Google Earth and the length is 4200 km. I am very confused how this happened.  Please tell me which number i should trust? Thanks!

    Liu Qiang

    Thanks for all your suggestions. Finally, I chose Behrmann projection, it has the similar results with google earth. 

  • Dileswar Nayak added an answer:
    Methods for modeling apple landscape using remote sensing and GIS?

    We would like to know a detail step by step procedure for land suitability modeling for Apple in higher mountain range. 

    Dileswar Nayak

    Thank you all for valuable suggestions

  • Shashi Gaurav added an answer:
    What is the standard difference between DTM, DSM and DEM especially with respect to the fast-changing geospatial semantics?
    These three terminologies can be confusing. Please shed more light.
    Shashi Gaurav

    But Raj where does the DEM stand. Differences between DSM and DTM is well understood but its DEM which is confusing. 

    Please visit below link for better understanding.

  • Lotfi Mustapha KAZI-TANI added an answer:
    Why do Vertisols show high values in redness index image?

    I applied redness index to Landsat ETM+ in my study region located in the North western part of Algeria. I’ve got quite good results concerning Mediterranean red soil but I couldn’t understand why the vertisols are as bright as or even brighter than red soil in the redness index image.

    Lotfi Mustapha KAZI-TANI

    @Sachin Patil

    The redness index is calculated as follow:

    RI=〖(B3)〗^2/((B1)*〖(B2)〗^3 )

    B1 : Reflectance of band 1 corresponding to the blue

    B2 : Reflectance band 2 corresponding to green

    B3 : Reflectance band 3 corresponding to red

    of Landsat ETM+

  • Hayder Dibs added an answer:
    How to calculate reflectance values from a photo taken with a modified camera?

    We have an Infragram Point & Shoot camera (a modified Mobius Action Camera whose low-pass filter was replaced by a red filter; For this modified camera, the "B" channel should be NIR. So, the "R" channel should be "red+NIR" and the "G" channel should be "green+NIR". We took a photo of leaves together with a Labsphere white panel. From the DN values of the three channels, how to calculate the reflectance values of NIR, red and green regions, respectively? How to calculate NDVI from the photo? Many thanks!

  • Antonio Ruiz added an answer:
    What are the methods for 3D City Modeling and which one is best?
    I want to understand the various methods used for 3D city modelling and their advantage, disadvantage.
    Antonio Ruiz

    You can get very nice 3D models from oblique aerial images and image matching. Acute3D does that. The problem with this technique is that the model you get is "dumb". It is only a triangulated mesh of unclassified points.

    Points from lidar can be classified easily and so it is easier to get semantically rich 3D models with classified objects: buildings with walls, roof, trees... If you have the vectors of building footprints you can get fully authomatic LoD2 models . If you don't have footprints you should do some editing to get acceptable 3D models. You can do that with Terrasolid software. The final building model is a boundary representation of roof planes and walls. You can attach textures form oblique images to walls and roofs. 

    You can get building models from point clouds from images and/or lidar also with CityGML. In this case, the buildings are selected from a library of basic building templates. 

    In general, point clouds from lidar have lower density than point clouds from image matching. The accuracy of elevation and slope is usually better with lidar but to place accurately the roof edges you need images. 

    The best 3D model depends on the application.  

  • Hayder Dibs added an answer:
    Does the modeling of the mathematical relationship between different global geoid models (say EGM2008 & EGM96) yield any kind of useful information?

    EGM2008 can be viewed as an improvement to EGM2008. Now the question is: Does the modeling of the mathematical relationship between different global geoid models (say EGM2008 & EGM96) yield any kind of useful information?

  • Alfonso Rodrigo Tierra added an answer:
    Are there any theoretical guidelines for geometrical Geoid modeling?

    Geometrical geoid modeling is a general problem to relate the GPS height to the quasi geoid. My question is: what are the criteria that guide the number of co-located points for problem modeling of the local geometrical geoid. Does it depends on the local topography?

    Alfonso Rodrigo Tierra

    When it use an artificial neural network to predicting (interpolation) the most important is that points are patterns that represent the behaviour of the geoid. In this case, is more important the pattern than the points density


  • Hayder Dibs added an answer:
    How the Geomatics/Surveying could move up the value chain and learn how to play in the broader information environment?

    How the Geomatics/Surveying could move up the value chain and learn how to play in the broader information environment?

     Do we need to adopt new business models, new service models, new ways of thinking, etc..

  • Aznarul Islam added an answer:
    Is there any open source website for getting litholog data for Ganges river basin?

    This is required for my Ph. D research

    Aznarul Islam

    thank u suvendu

  • Hayder Dibs added an answer:
    Does the calibration practice of oil tanks take full advantage of geomatics or surveying engineering?

    Through my professional carrier I engaged in several aspects of tanks calibration in the petroleum industry and I visited different aspects of the current practice and the current literature. Through this experience I got the feeling that the tanks calibration practice is not well served by the surveying or Geomatics engineering. I do believe that this sector can be advanced if it is deeply connected with   Geomatics. I do appreciate your feedback.

  • Chon Le Trung added an answer:
    Is there a program converted the EGM96 spherical harmonic coefficient set to their ellipsoidal harmonic coefficient counterpart?

    Is there a program converted the EGM96 spherical harmonic coefficient set to their ellipsoidal harmonic coefficient counterpart?

    I'm looking for a program to converted spherical harmonic coefficient (EGM96 or EGM2008) set to their ellipsoidal harmonic coefficient .

    To develop this synthetic set of coefficients

    Or how to get ellipsoidal harmonic coefficient of any EGM

    Chon Le Trung

    Dear Abdel

    Please access to this link to get more information about EGM96 and EGM2008

  • Gamal Seedahmed added an answer:
    How to make soil Maps from point data?
    I have 100+ point data of soil type, for example at point x soil is "clay", at point y soil is "clay-sand", at point z soil is "sand" and so on. Now i want to generate soil map/surfaces. Kindly help me if anyone has some solution, suggestions or free software.
    Gamal Seedahmed

    A short answer to your question is the following. First you need to interpolate your data to a regular grid. Then you can use a GIS software such as ArcGIS to generate your map.

  • Thorsten Reitz added an answer:
    How can I create IndoorGML format for my building object?

    IndoorGML is new standard for indoor navigation network. I have building obejct in format obj, skp and I need create indoorGML. What application? Transform format? Thanks

    Thorsten Reitz

    IndoorGML has a very rich semantic object model that will be hard to get from OBJ or Sketchup files. It is based on OGC GML and has structures more like IFC/Revit/CityGML than OBJ or SKP.

    In any way, you can have a go with Safe Software's FME to attempt a conversion; use the schema-driven GML writer as a target. At least my version doesn't support IndoorGML directly yet.

    An open source alternative might be to export your SKP models to KML/Collada and then use HALE ( to transform to IndoorGML. This process would enable you to build up the semantic structure of IndoorGML.

  • Morten Wergeland Hansen added an answer:
    Does anyone know any software or toolbox uses to estimate the wind direction from SAR images?

    we will try to estimate wind speed and wind direction using SAR images, we used nest tool box, but it is limited fro C-band.

    Morten Wergeland Hansen

    You can use our open-source OpenWind package written in Python ( Note, however, that wind direction is not estimated from the SAR images but we use apriori wind directions from models (default is ncep forecast). The master branch of the git repos is stable and depends on another package called Nansat (you'll find information on github). There is also an algorithm to estimate the wind field using a Bayesian minimalization scheme under the develop branch. When Sentinel-1 has the Doppler shift included in the data product, this can be used to also improve the wind directions. Hope it helps!

  • Brian Carcich added an answer:
    How to calculate sunglint regions from geometry?


    I'm trying to compute probable region of sunglint to use as a mask in the processing of remote sensing data. There are several methods for sunglint flaging using spectral characterizations, but I found only one reference to flag sunglint regions based on observation geometry (Mailhe et al. 2004, attached); that is more suitable for my application, but I'm having a hard time to perform the calculations.

    One of the information required is the Earth-Sun unit vector for the epoch of observation; In the calculations of Mailhe et al. 2004, the J2000 Geocentric Celestial Inertial frame (GCI) is used for the computations. One possible source of such data is the NAIF SPICE toolkit (; what I understood from the documentation is that the implemented J2000 reference frame actually represents the International Celestial Reference Frame (ICRF), that has its origin on the barycenter of the solar system, whereas the GCI J2000 has its origin on the barycenter of Earth. Nevertheless, the documentation also states that all calculations are relative to two selected bodies, with the origin playing a limited role (basically correction). In summary, I could not understand if the data from this source is appropriate for the calculations. The paper from Russel (1971, on the link) show an approximate formulation for GCI (but not J2000) with accuracy that should suffice for this application, but again I'm not sure if this is adequate. Perhaps it does not make much difference if the reference frame is kept constant through the computations?

    The radial direction of the pixel center and the radial direction of the satellite must also be calculated. I followed the guidelines provided by Hapgood (1992, attached) to convert geodetic latitude, longitude and altitude from spherical to cartesian representation and them to GEI (which I understood is a synonym to GCI). I assume that this would be compatible with the Earth-Sun vector determination of Russel; nevertheless, the SPICE toolkit could also be used for these transformation to keep compatibility of reference frames if the SPICE Earth-Sun vector should be used.

    Can anyone provide me with references and/suggestions about the sunglint geometry and Earth-Sun vector calculation?

    Best regards,

    + 2 more attachments

    Brian Carcich

    You are very welcome, and thank you for the challenge.  I'm a bit of a SPICE evangelist and while I am not part of NAIF at JPL, the NAIF group at JPL is always looking to reach out and I like to support them (as they have supported me).  I think this particular problem would make an excellent case study for using SPICE, and I will probably bring it to their attention at some point.

    The funny part for me is that the code that solves the problem is usually just a few SPICE calls, but the steps to get to those calls is what takes up most of the code.


  • Hayder Dibs added an answer:
    How can one normalize raster in ArcGIS?

    I have two raster files (.TIFF) with changes in temperature and precipitation for two reference periods. I was trying to use ArcGIS 10.2 to normalize the values from 0 to 1 in order to use it for my research, but everything I try results in error of a different kind. I tried to use:

    1. Raster Calculator: (raster - mean) / stdv works, but the next step: ( raster - min(raster) ) / ( max(raster) - min(raster) ) results in error

    2. Transformations tool from Geomorphometry & Gradient Metrics toolbox: I get this error every time:

    RuntimeError: Object: Error in getting parameter as text

    Failed to execute (transformations).

    Coming from the agricultural sciences and hardly calling myself a GIS expert, I would appreciate any advice from you.

    Thanks in advance.

  • Muntadher Aidi Shareef added an answer:
    How can we calculate the correlation length from images?

    I would like to calculate the correlation length using radar image. Can you tell me what the easiest procedure to calculate the correlation length of the radar images is?

    Muntadher Aidi Shareef

    Thanks dear  Younes Khosravi and Jahangir Pachkam I will try it;

  • Mustafa Üstüner added an answer:
    What classification technique is suitable with image fusion (SAR and Optical imagery) for improving land cover classification?

    My research is focusing about fusing SAR and optical imagery for improving land cover classification that specially maize crop. I'm not sure that ANN, SVM or DT technique, which one's better for agriculture. Do you have a idea?

    Mustafa Üstüner

    Please see the article below. 

    Björn Waske, Matthias Braun, Classifier ensembles for land cover mapping using multitemporal SAR imagery, ISPRS Journal of Photogrammetry and Remote Sensing, Volume 64, Issue 5, September 2009, Pages 450-457, ISSN 0924-2716,

  • François-Nicolas Robinne added an answer:
    Using remote sensing tool, what is the simplest method to use for studying the forest fire risk in a mediterranean region?

    Regardless of the form or method used, should we take consider all biotic and abiotic factors of the physical environment or only the climat indicator (IC) and topography indicator (ITP) ?

    Thank you for answering my question.

    François-Nicolas Robinne

    Allessandro is right, niche modelling using the maximum of entropy approach has proven its usefulness. There are several software which implement it, like MAXENT or ModEco.

    This paper might be of some interest as well: "Spatial variability in wildfire probability across the western United States", Parisien & al

  • Andreas Paul added an answer:
    In what real-world examples do users still digitize features from a map?

    Is digitizing of map features completely dead?

    For example, when and why do you still digitize features from a map?

    It can be heads digitizing up from a scanned paper map (or image, or whatever) or using a traditional digitizing tablet. It can also just be digital and heads-up (i.e. you never had the paper map).

    Do you ever still utilize manual feature digitization to create points, lines, or polygons?

    I need this information for a statistical technique I am developing.


    Any VGIS examples?

  • Fábio Marcelo Breunig added an answer:
    Are MODIS C5 Vegetation Index products corrected for topographic shadows?

    Obviously MOIDS VI products are corrected (to some extents) for cloud shadows. But how about topographic shadows? If yes, any information on DEM and methodology used for corrections?

    If no, to what extent do you think VIs (particularly NDVI) in C5 are affected by topography and illumination/viewing geometry? As far as the general appearance of the vegetation cover is concerned, my focus is not on "trees", but mostly on grass, shrubs, and subshrubs. Can I also have some suggestions from your own experiences with correcting topographic, viewing/illumination effects on NDVI?

    Fábio Marcelo Breunig


    The tpographic shadows are not addressed, as well directional effects.

About Geomatics

Geomatics is a synergism of various disciplines - Geographical Information System (GIS), computerised databases and applications, computer science, graphical processing, cartography, photogrammetry, statistics, remote sensing etc. The applications of Geomatics includes the real-world problems of management of natural and man-made environment and of the objects related to it. This would encompass the fields of natural resources management, resources planning and decision-making etc.

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