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Modelling archaeological layers as 3D polygons

ArmandoMelo

Dear all,

I’m new to this forum and new to 3D GIS, though I’ve been using ESRI software for some time. I am trying to use ArcMap and ArcScene to solve an archaeological issue: I need to link archaeological finds to their stratigraphic layers and excavation units.

I thought I could work with projections of the finds (points, XYZ data) and the layers/units (as 3d polygons) to cross information between both, by means of “select by location”, i.e. select all points that “are within” a certain layer or unit polygon. Indeed, I ended up with a selection of points/finds in ArcScene but apparently the elevation data of points was not taken into consideration, that is, all points within the polygon area (2D) were selected, regardless of their respective Z values. I also tried “Inside 3D”, with the same results.

So, my question at this point is: am I doing something wrong and/or skipping some important step of the process, or is ArcGis capable of/suitable for this type of operation at all? In other words, and assuming that my 3D projection of the finds (points) is correct (which would seem to be the case), are the polygons really 3D and Z aware, or only partly so, or not at all…?

Has anybody tried something like this before? Any contributions or comments would be much appreciated, I’m at a total loss right now. Thanks a lot for your time!

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Accepted answers

XanderBakker

When working with 3D polygons (Z aware polygons) the polygon vertices may have a Z value, but the polygon does not have a volume. The tool Interpolate Polygon To Multipatch (3D Analyst), can create a Multipatch which has a volume.

When you have multi patches, you can use Inside 3D (3D Analyst) to determine if they are inside.

All comments

XanderBakker

I created a blogpost of what I did based on the data that Armando Melo sent to me privately. You may be interested to have a look at it: Modeling Archaeological Layers

RyanMoritz

Hello Armando,

I realize that you have not been active on this post for some time now but I am curious if you have made any new progress on this thread since your last post? I am in the midst of creating a 3D model of my thesis site and I am wondering if a more straight forward approach has been discovered in the year and a half since your last post. Has anyone in this thread used ArcGIS Pro? Does it's capabilities make this task easier?

Ryan

ArmandoMelo

Hi Victor, Xander and All,

I’m very sorry for the delay, other things got in between and I’ve been in and out of connection due to heavy storms. Still, I managed to work some more on the GIS project and retrace my steps on “clean” documents. Inside 3D definitely works, so:

Victor – I’m real glad you find this useful, please keep me briefed on your results/issues and on any developments/improvements of the method, I’m very interested, thanks in advance. My topographic points are actual surface measurements taken as-we-dig, not elevations from profiles or cross-sections. The resolution changes between different stages of the excavation, from 9 points per square meter on the earlier “sondage” phase to an average of 20 points for an area of some 11 square meters, which is not much but still seems to produce reasonably accurate surface TINs. I have draped georeferenced photos of the surfaces over the TINs and also over the extruded polygons, with satisfying results in terms of the correspondence between surface features and TIN elevation. But this is a very good point, if TINs are oversimplified, the whole method is a waste of time, as it will produce misleading results. And yes, finds located close to the boundaries of a deposit are an issue, even during excavation, because the deposit in this particular site is a mostly loose, sandy sediment with a strong probability of small-scale vertical migration of finds between occupation horizons. I still have to decide how to deal with the issue…

Xander – I’m sending you the data and I really appreciate your willingness. No major expectations, it would just be great that you could give it a try, if and when you can spare the time. Even negative results would be welcome, at least I would know it is a “no can do” thing!

What I have achieved so far goes like this:

Question:

Which finds belong to each archaeological unit?

Data:

Point feature classes (XYZ, Shape=Point ZM) with the topographic points corresponding to the top and bottom surfaces of each archaeological unit (OH – occupation horizon)
Point feature class (XYZ, Shape=Point ZM) with the finds
Polygon feature class (2D) covering the excavation area

Method (ArcScene):

Create TINs for each OH surface (top and bottom) [ArcToolbox>3D Analyst Tools>Data Management>TIN>Create TIN]
Create individual 3D polygons for each OH, with the corresponding surface TINs as “Input TINs” (top and bottom) and the 2D excavation area polygon as the “Input Feature Class”; this seems to work better if the first input TIN is the bottom surface [ArcToolbox>3D Analyst Tools>Triangulated Surface>Extrude between]
Close the resulting 3D polygons [ArcToolbox>3D Features>Enclose Multipatch]
Check whether it is totally closed using “Is Closed 3D” [ArcToolbox>3D Features>Is Closed 3D]
Run “Inside 3D” to Identify the “finds” points that belong to each 3D polygon, using the “finds” feature class as the “Input Feature Class” and one of the 3D “OH” polygons as the “Input Multipatch Features”; the output is a table [ArcToolbox>3D Features>Inside 3D]
Join the “finds” feature class table with the “Inside 3D” output table, using the FID field from the former and the TARGET ID field from the latter
On the “finds” feature class table, select all points marked as “Inside” to see a projection of the finds belonging to that particular OH

This time around I skipped the “Interpolate Polygon to Multipatch” step, as the extruded polygons are already multipatch features. I still have to do more testing, in order to check the real need to close the multipatches. “Inside 3D” seems to work with not-closed polygons as well but I would have to compare results from different attempts to see what is more accurate. I have tried the above method a few times by now and it seems to work, but I would stress the need for more testing and comparing results at this stage. The method must be totally accurate or else it is useless to me – no data is better than bad data!

I’ll keep you informed of further developments, any comments/improvements would be much appreciated, thanks for your time.

Armando

ArmandoMelo

Hi Victor,

Thanks for your interest, I'm glad to see that someone else faces the same issues. Thanks also for the solution, indeed in my early attempts the point feature class was not 3D but at a certain stage I also thought that this could be the problem and made it 3D, using 3D Analyst's "Feature to 3D by attribute", and the Shape field now is "Point ZM" so it should be 3D, but the selection still doesn't work right.

BTW, I've been reviewing some recent litterature on the subject of GIS uses in Archaeology and came across some interesting papers, namely Preparing the Paliambela Kolindros Archaeological Project digital archive for long term preservation by Marcos Katsianis (2012), who quotes from Alistair Ford's (2007)

Visualizing Integrated Three-Dimensional Datasets. Modelling data in the geodatabase using multipatch features. According to Ford, and as Xander rightly pointed out, the solution is using Multipatch features, so that "(...) spatial entities can be represented with true three-dimensional features and still be queried and selected and have full attribute data (...)". But Ford also refers that "The multipatch feature cannot be created in normal edit sessions in ArcMap as with the standard ESRI geometry types. These features must be created using ArcObjects (...) or from raw data sources."

Unfortunately, this sounds a bit "out of my way", I'm only an archaeologist and software user, and by no means a programmer or developer. I'm really looking for some straightforward solution, without having to become proficient in external 3D software and/or programming languages, but I'm starting to think that there isn't one right now... Anyway, I hope those papers may be of some interest to you or anyone else on GeoNet, I'll keep searching and I'll certainly post any solutions or useful information, or a friendly goodbye message when I give up...! Thanks for your time!

VictorKlinkenberg

Hi Amando,

I have struggled with the same issues in the past, also in an archaeological context. I haven't tried these operations yet with arcgis 10 but I recognise your problems from previous versions.

One possible solution: have you made sure that your point feature class is 3D (so not Z as attribute data)?

Let me know if you found an answer to these issues!

Victor

ArmandoMelo

Many thanks for a quick and clear reply. OK, I was afraid 3D polygons did

not really have a volume, now I know for sure...!

I have tried your suggestion but no results so far, apparently I cannot use

it with my previously extruded polygons and as the tool only accepts one

input surface, I don't see how I can get the right kind of volume, as I

have to include the top and bottom surfaces of each volume, according to

field data (XYZ topographic points). Those surfaces are the stratigraphic

limits of layers or excavation units.

Anyway, I tried before with multipatches, I used "enclose" and/or checked

with "is closed" and also tried "inside 3D", but the resulting selection

of finds/points always includes points that are way above the polygon.

Actually, all points within the polygon's XY area are always included,

regardless of their Z values. BTW, the point feature class does include Z

values and projects OK in ArcScene.

XanderBakker

When you have multi patches, you can use Inside 3D (3D Analyst) to determine if they are inside.

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