Hot answers tagged measurements
8
Accuracy of calculated results depends on a number of discrete processes, which can all compound inaccuracy in the final dataset.
The importance of Metadata in this situation, is it can be used to explain error and even identify steps error is introduced.
The most important thing is to understand that ground truthing your results, if performed correctly ...
7
If you're home-brewing in the browser, you can get a "circle" (it will not be round on the screen due to your projection; rather approximated by a polygon w/ as many points as you care to draw), use a the direct form of geodesic calculations: given a point, a direction (azimuth), and a distance it gives you the resulting point. Gory details: ...
6
Your suggestions sounds fine. Also every geometry object has a distanceTo() function which can be used like:
geometry.distanceTo(anothergeometry)
EDIT:
After more thought and testing the example, i think it would be easiest for you add new layer for labeling purposes. Possibly a layer of just points which you would set the labelXOffset and ...
5
Here is copy-paste from one of my old applications. EDIT: I modified getCustomLength, so it should work with different coordinate systems. Fiddle: http://jsfiddle.net/A78Zu/
measureControl = new OpenLayers.Control.Measure(
OpenLayers.Handler.Path,
{
immediate: true,
persist: true
}
);
measureControl.getCustomLength = ...
5
A little theory: When using a geographic (non projected) coordinate system, such as WGS84, all measurements which are made using planar geometry (calculations on a plane) are wrong. The bigger the area, the bigger your error. To have precise measurements on the ellipsoid, qgis would need to implement great arcs, etc...
QGis is suggesting that you project ...
3
You can use the 'Calculate Geometry' (Right click on an field in the attribute table) tool to determine the area of each polygon and then use the 'Summary Statistics' (in the Analysis toolbox) with the owner name as a Case field and the area field set to sum will produce a table that shows the total area for every unique entry in the owner name field.
Here ...
3
Qgis wants you to define a projection system to be used in your project. It wants it so if you're going to import something from the "real" plane (remember that the earth is spherical) to know where it should go in the Cartesian plane.
There are numerous projection definitions ready to be used that were tailor made as solutions for specific problems. Proj4 ...
3
OpenLayers only allows for drawing
circles using planar distances
To get a geodesic circle, you could use the buffer operation in ESRI's geometry service.
...if unit is linear such as feet or
meters, geodesic buffering is
performed
A freely accessible one is available here.
3
@ MaryBeth - You have valid concerns, It probably is not ever going to be as easy to "draft" in arcmap as it is in autocad, or microstation, or "Their/Your CAD System Here".
*EDIT: * what's new
There are some SUPER nice features however that I am beginning to really love in desktop 10.
ESRI has come a long way to making or facilitating a (used to be ...
2
I want to be able to call this
function after a MouseEvent.MOUSE_MOVE
event in order to measure the line on
the fly
First off, some words of caution.
I implemented similar functionality in a Flex app awhile back
i.e. When user moved mouse around the map, it kept pinging the geometry service for the distance or xy coordinates and displayed it ...
2
Are you definitely working with a projected shapefile? If the shapefile is in ArcMap, right-click on the shapefile, click on Source and look to see that is in a Projected Coordinate System rather than a Geographic Coordinate System
If it's geographic, go to Data Management Tools ->Projections and Transformations -> Feature -> Project. Then add the ...
2
A spatial join in the other direction associates the closest distance of the line layer to each object feature. Querying for distances of 120 m or less solves the problem.
Alternatively, you can compute the Euclidean distance grid for the line layer, compare the grid values to 120 m, and use the result to select objects. Selection can be done by ...
2
I would say you cannot georeference this or use geografical coordinates. It doesn't matter where in the room (and in the world) this turntable lays, right? I think you need to create your own local plane coordinate system, measuring by a ruler the size of the turntable, then referencing (scaling) the image to this distance (presented as a vector line or a ...
2
you have to change some code in qgis-web-client / site / js / WebgisInit.js
you can add unit parameter to OpenLayers.Control.Measure method. you have to do this for polygon too...
measureControls = {
line: new OpenLayers.Control.Measure(
OpenLayers.Handler.Path, {
persist: true,
units:'ft',
handlerOptions: {
...
1
Field calculator uses the CRS of the shapefile, while measurement tool uses the projects CRS, until you uncheck Use ellipsoid
The two CRS may be the same, or not.
You can right-click on the layer -> Set Layer CRS for Project, unless you are using openlayers plugin for background layer.
1
I would write a script to run across a list of X,Ys on your constraint and compare distances. This may be slow if you have a large number of constraint points. I am not super experienced with scripting in QGIS, but my initial thought would be something like this (python):
import math
sub=[1003017.999854, 211253.000116] #X and Y coordinates of the subject ...
1
Create a field in the attribute table to store the acreages. Do a select by location query that intersects the parcels with your mask. In the attribute table right click on the name of your new field and use the Geometry Calculator. You can select acreage from there.
You'll need to specify a projection, hopefully your data is in UTM or State Plane.
This ...
1
Sounds like a 'Level of Service' type analysis?
The Transportation Research Board have published a 'Transit capacity and quality of service manual' - containing a section specifically on 'Quality of Service', and the analysis of the various measures of quality of service. http://www.trb.org/Main/Public/Blurbs/153590.aspx
An example of how this has been ...
1
As far as I can tell there is no interface for the measure tool dialog and thus no way to close it using ArcObjects. I think you'll have to use the Windows API functions FindWindowEx to find the child window handle corresponding to the measure tool dialog, and DestroyWindow to close it and release its memory resources.
See pinvoke.net for C# function ...
1
The coordinates look like degrees decimal-minutes. You'll need to convert them to decimal degrees to import them as WGS84. Do this in excel and then add the table to ArcGIS as an Excel table. Then create an XY Event layer from the coordinates. Finally, convert this to a geodatabase feature class of shapefile.
If you want to measure the distances between ...
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