# Geomatics

What are the best institutions to study Remote Sensing for pasture and natural grasslands worldwide?
I am looking for a place to send a student to spend about six months developing a research project in this thematic area
Wendy Griffiths · DairyNZ
If the student wants an experience downunder - Ian Yule at Massey University, NZ http://www.precisionagriculture.org.nz/about-us/new-staff-holder/new-staff-member-page-4/
How can one orthorectify LISS-4 MX data in Erdas Imagine?
To orthorectify any image RPC file is needed. How to obtain RPC file for LISS-4 data?
Cristina Radnea · National Research and Development Institute for Soil Science, Agrochemistry and Environmental Protection
I don't think it will work, but try to put this question to the data provider; he is from your country, isn't he ?
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.
Peter Mwangi · Jomo Kenyatta University of Agriculture and Technology
This is the case for me, and the average gives a new look that's a consensus
Fitting variogram model with NLS in R
I tried to compare the result obtained by fitting the spherical variogram model using fit.variogram and nls functions. The large difference in the results is a great concern for me knowing that the two functions use Weighted Least Squares (WLS) approach for estimating parameters. The steps taken are as follows: ## Fit empirical semivariogram using gstat empvar<-variogram(yield ~ 1,canmod.sp,cutoff= 400,width = 25, Cressie=TRUE) # Fitting Spherical variogram model to sample variogram sph.var<- vgm(psill =130, model = "Sph", range = 65, nugget = 180) sph.mod<-fit.variogram(empvar, model = sph.var) print(sph.mod) The result obtain from fitting the spherical model to sample variogram is sph.mod model psill range 1 Nug 230.917736411 0.0000000000 2 Sph 108.323055319 87.6889385431 The non-linear least squares (NLS) approach use by default s Gauss-newton algorithm in an iterative search process. I used the initial values obtained from the empirical variogram above (psill=130, range=65, and nugget=180) as starting values for the iterative procedure. ## Define Spherical Variogram functions for NLS sph.vgram <- function(dist, range, psill, nugget){ dist <- dist/range nugget + psill*ifelse(dist < 1, (1.5 * dist - 0.5 * dist^3),1) } ## Fitting spherical with NLS fit.var <- nls(gamma~sph.vgram(dist,range,psill,nugget),data = empvar, start=list(psill=130, range=65, nugget=180),trace=T) The result obtained from the nls fitting is Nonlinear regression model model: gamma ~ sph.vgram(dist, range, psill, nugget) data: empvar psill range nugget 90.7071423 342.1025007 278.9542178 residual sum-of-squares: 1140.67875 Number of iterations to convergence: 18 Achieved convergence tolerance: 9.79837651e-06 Could anyone explain why large difference in the two result? Is the R script for fitting the NLS right? I am worried for having such disparity. Thanks while looking forward to reading your suggestion, comments and advice. Moshood.
Richard Telford · University of Bergen
fit.variogram is weighted by the number of observations in each distance class - see help file for details. That might explain the difference between the fit.variogram results and the nls results.
What GPS mapping software do you use?
I'm looking for the best in class software solutions with which you can do the following: a) define a map with territorial units (e.g. district, region, country, etc.), b) import GPS coordinates and another associated variable (e.g. self-reported well-being), c) calculate the average per territorial unit of these associated variable values, d) colour-code the average values from min to max, e) export the map.
Natheer Alabsi · The University of Tokyo
you can try Trimble GPS Analyst extension for ArcGIS
Besides LiDAR, through which other means can you generate powerful point cloud data nowadays?
Feature extraction
Nashon Adero · Oakar Services Ltd
Can anyone tell me on what basis the areas of each state and country (referring to India) have been calculated and published as official figures?
I am told that adding the area of various Survey of India Toposheets for a state does not add up to the official state area. Moreover, the satellite images after geo-referencing also tend to have inaccuracy. So while generating district-wise statistics for say, land cover and land use, and adding them up, the total land area does not tally with the official state area. How to solve this?
Uttam Laisram · DST, Manipur
Thank you Ana-Maria. Yes, the same projection is a must and sometimes this was overlooked. More importantly. what I really want to understand is who measured the sizes of countries and states, as found in encyclopedias and official publications, and whether the methodology followed then holds accuracy till date.
How can I simulate the SAR backscattering and compare with dielectric constant that measurement in situ and laboratory?
I was searching about some model but I don't know how can I apply, in addition those model is semi empirical or empirical but I don't have surface roughness data from field it is other problem.
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.
David Kuria · Dedan Kimathi University of Technology
There are many methods for interpolating a surface from a point cloud. These vary from the simple IDW to the Kriging method. Most of the GIS solution around (both closed and open source) support these methods and so the best for each case will depend on your requirements e.g accuracy of the representation, availability of a validation dataset and so on. One way of evaluating could be designating a part of your initial point cloud data as validation dataset and using the remainder in the interpolation, after which you compute statistics of correlation between interpolated values against the actual values from the validation dataset.
How to extract DTM from a map?
I want to extract DTM from a map of 1:50,000 scale. How can I do it?
You can derive the contour with the radar images (using GlobalMapper), then export the contour to MapInfo or ArcGIS and reproduce the DEM.
What is the best way to connect Matlab and Visual Studio by DLL?
Looking for a way to input ArcGis to Matlab
Samira Sanginian · Khaje Nasir Toosi University of Technology
Thanks all of u for guidance,this problem dissolve in matlab 2012 with export dll to .net
Best practices for georeferencing with ArcMap 10 – transforming the raster: how to assess a georeferencing strategy?
According to ESRI’s online resources (http://resources.arcgis.com/en/help/main/10.1/index.html#/Fundamentals_of_georeferencing_a_raster_dataset/009t000000mn000000/), spline transformation should be used for local accuracy, that is when we are “sure” of the position of the control points. Polynomial transformations guarantee global accuracy. In this context, what RMS error should be expressed? I guess I cannot compare a RMS error yielded by a polynomial transformation with a RMS error given by a spline transformation (?). When should I use spline transformation and when a polynomial one (and which order)? For example, would make sense to use spline transformation with as many control points as possible (30-50 or even 100) for georeferening aerial photos (known for their distortions)? What about a 3rd order polynomial transformation for this case? Are there certain standards/best practices for various situations?
Dwight Barry · Group Health Cooperative
I think spline is generally a better approach; here's a classic paper on it: http://skagit.meas.ncsu.edu/~helena/gmslab/papers/IEEEGRSL2005.pdf Hengl's book (http://spatial-analyst.net/book/download?size=thumbnail) has lots more details, e.g., from pages 13-14: "In the case of a moving surface, for each output grid node, a polynomial surface is fitted to a larger number of points selected by a moving window (circle). The main problem of this technique is that, by introducing higher order polynomials, we can generate many artifacts and cause serious overshooting of the values locally (see further Fig. 1.13). A moving surface will also completely fail to represent discrete changes in space.... A spline is a type of piecewise polynomial, which is preferable to a simple polynomial interpolation because more parameters can be defined including the amount of smoothing."
I am into Urban Designing but have a strong Geomatics background, I want to carry out some research in integrating the two through SDI initiatives.
A scenario is a granting town status to a new town, how can one develop an SDI to help in sustainable development of that town?
Gabriela Droj · University of Oradea
SDI as Spatial Data Infrastructure ???
• How does one use the product MOD43A3 (Albedo) in environmental studies?
It's the first time I have used MOD43A3, I would like to know how to use the images referred to as black-sky albedo and white-sky albedo. Which is used for environmental studies? I'm looking to get a variable to represent the land surface albedo.
Miguel Armando López Beltrán · Universidad Autónoma de Sinaloa
Thanks Ruxandra Vintila
Russia on the other side in GCS WGS 1984 world shapefile
I have a world shapefile with a GCS_WGS_1984 coordinate system. Due to obvious reasons, in ArcMap a small part of Russia is showing in the leftmost side of the data frame. In ArcGlobe, the layer is fine, now can I change the projection of the shapefile to some other coordinate system to show Russia as one in Arcmap (as I am interested only in the Asia Pacific region). Or do I have to manually modify the shapefile and join the country forcefully?
Chitrini Mozumder · Asian Institute of Technology
thanks all. finally I solved my problem by this: 1. Load the data into ArcMap and open the Data frame Properties dialog (View | Data Frame Properties). 2. Click the Coordinate System tab and then click the New button. Choose Projected Coordinate System from the popup menu. 3. Give the projection a name like "Pacific Rim View" or whatever, and choose the "Plate Carree" projection from the Name list. This is a "fake" projection in that it doesn't majorly change the rectangular shape of the unprojected world data, but it does convert lats/longs into metres. 4. Set the Central Meridian value to 120. 5. Click the Select button in the Geographic Coordinate System group and choose World | WGS 84 (assuming that's what your data are in; just be sure to match the data's native coordinate system here.) 6. Once you've done that, click OK on both dialogs to redraw the world map, centred on the PACRIM. If you want to permanently change the data, you can perform similar steps to these by using the Project Wizard in ArcToolbox (ArcToolbox | Data Management Tools | Projections | Project Wizard). Just follow the wizard steps and you'll see exactly the same dialogs pop up in all the important steps.
In QGIS - how difficult is it to bring DD MM SS data in?
The current project standard for working with GPS data is Decimal Degrees. There is however an ever ongoing conversion that is taking place to allow for the use of decimal degrees. I am therefore interested to obtain your input on how difficult it would be to bring DD MM SS data directly in from the GPS to map it. What would the procedure be?
There are other options like GPS track marker http://www.trackmaker.com/downloads.php. This is one of the most convenient way of downloading data from GPS. The save as one of the readable formats. The data will have only spatial reference. So you can add columns for lat and long values and save them.
Goce data.
I am working in a spatial data mining model of gravimetry. For sparsely sampled, I am using satellite gravity data, especially ESA GOCE data. I have difficulties in processing the raw data, can someone help me?
Gábor Timár · Eötvös Loránd University
Dear Miguel, raw data processing of satellite gravimetry is quite complicated and needs min. a year to learn for practical use. If you want to mine geoid data in sparsely surveyed regions, it would be better to search for the *results* instead of raw data. Anyway, I do support your decision: to use satellite gravimetry for those regions. It is a common mistake to use high order and rank global geoid models - however they are of high-resolution only in densely surveyed regions. Up to 60th order and rank, these models use 'traditional' satellite gravimetry (perturbation analysis of the orbit elements) - all of the further details came from ground surveys. The up-to-date experiments (GRACE, GOCE, CHAMP) could refine the global geoid up to cca. 150th rank and order. With all of this, if you have just a few local field gravity measurements, it could significantly increase the realiability of your geoid data. Using Stokes is much more easy than processing GOCE ;) Sorry for the length and for being partly off-topic, Gábor
Layer stacking in Python:
I have 4 NDVI images (0NDVI.tif, 1NDVI.tif, 2NDVI.tif, 3NDVI.tif) saved in a folder (VI). I want to create a layer stack by using Python script. Can anyone tell me how to do this?
Grzegorz Knor · Institute of Fundamental Technological Research
If you are familiar with ImageMagick you can do it in console: convert *.tif multipage.tif In Python there is a PythonMagick, which provides object oriented bindings for the ImageMagick Library: http://www.imagemagick.org/download/python/
• Sunday Goshit asked a question:
Does anyone have the erdas or envi model for the geostatistical neighborhood similar pixel interpolator?
I am comparing methods for data filling for Landsat ETM+ SLC-off
• Anders Erickson asked a question:
Geocoding Canadian postal codes spanning over multiple years and the PCCF
Any researchers out there geocoding Canadian postal codes that span a decade using the StatCan PCCF? I'm trying to figure out the PCode Birth and Retirement dates and using different updates of PCCF is appropriate.
• Nirzar Lakhia asked a question:
When will the RISAT-1 Images be available to researchers?
Indian Space Research Organisation's workhorse launch vehicle PSLV yet again proved its reliability completing its 20th successful flight in a row launching RISAT-1, the heaviest satellite ever lifted by it.
• Nirzar Lakhia asked a question:
• Nirzar Lakhia asked a question: